With Grails' default settings you can actually develop an application without doing any configuration whatsoever. Grails ships with an embedded servlet container and in-memory H2 database, so there isn't even a database to set up.

However, typically you should configure a more robust database at some point and that is described in the following section.

You can add your own configuration in here, for example:

foo.bar.hello = "world"

Then later in your application you can access these settings in one of two ways. The most common is from the GrailsApplication object, which is available as a variable in controllers and tag libraries:

assert "world" == grailsApplication.config.foo.bar.hello

The other way involves getting a reference to the ConfigurationHolder class that holds a reference to the configuration object:

import org.codehaus.groovy.grails.commons.*
…
def config = ConfigurationHolder.config
assert "world" == config.foo.bar.hello

ConfigurationHolder and ApplicationHolder are deprecated and will be removed in a future version of Grails, so it is highly preferable to access the GrailsApplication and config from the grailsApplication variable.

• grails.config.locations - The location of properties files or addition Grails Config files that should be merged with main configuration
• grails.enable.native2ascii - Set this to false if you do not require native2ascii conversion of Grails i18n properties files
• grails.views.default.codec - Sets the default encoding regime for GSPs - can be one of 'none', 'html', or 'base64' (default: 'none'). To reduce risk of XSS attacks, set this to 'html'.
• grails.views.gsp.encoding - The file encoding used for GSP source files (default is 'utf-8')
• grails.mime.file.extensions - Whether to use the file extension to dictate the mime type in Content Negotiation
• grails.mime.types - A map of supported mime types used for Content Negotiation
• grails.serverURL - A string specifying the server URL portion of absolute links, including server name e.g. grails.serverURL="http://my.yourportal.com". See createLink.

War generation

• grails.project.war.file - Sets the name and location of the WAR file generated by the war command
• grails.war.dependencies - A closure containing Ant builder syntax or a list of JAR filenames. Lets you customise what libaries are included in the WAR file.
• grails.war.copyToWebApp - A closure containing Ant builder syntax that is legal inside an Ant copy, for example "fileset()". Lets you control what gets included in the WAR file from the "web-app" directory.
• grails.war.resources - A closure containing Ant builder syntax. Allows the application to do any other other work before building the final WAR file

For more information on using these options, see the section on deployment

The Basics

Grails uses its common configuration mechanism to provide the settings for the underlying Log4j log system, so all you have to do is add a log4j setting to the file grails-app/conf/Config.groovy.

So what does this log4j setting look like? Here's a basic example:

log4j = {
    error  'org.codehaus.groovy.grails.web.servlet',  //  controllers
           'org.codehaus.groovy.grails.web.pages' //  GSP
    warn   'org.apache.catalina'
}

This says that for loggers whose name starts with 'org.codehaus.groovy.grails.web.servlet' or 'org.codehaus.groovy.grails.web.pages', only messages logged at 'error' level and above will be shown. Loggers with names starting with 'org.apache.catalina' logger only show messages at the 'warn' level and above. What does that mean? First of all, you have to understand how levels work.

Logging levels

The are several standard logging levels, which are listed here in order of descending priority:

1. off
2. fatal
3. error
4. warn
5. info
6. debug
7. trace
8. all

When you log a message, you implicitly give that message a level. For example, the method log.error(msg) will log a message at the 'error' level. Likewise, log.debug(msg) will log it at 'debug'. Each of the above levels apart from 'off' and 'all' have a corresponding log method of the same name.

The logging system uses that message level combined with the configuration for the logger (see next section) to determine whether the message gets written out. For example, if you have an 'org.example.domain' logger configured like so:

warn 'org.example.domain'

then messages with a level of 'warn', 'error', or 'fatal' will be written out. Messages at other levels will be ignored.

Before we go on to loggers, a quick note about those 'off' and 'all' levels. These are special in that they can only be used in the configuration; you can't log messages at these levels. So if you configure a logger with a level of 'off', then no messages will be written out. A level of 'all' means that you will see all messages. Simple.

Loggers

Loggers are fundamental to the logging system, but they are a source of some confusion. For a start, what are they? Are they shared? How do you configure them?

A logger is the object you log messages to, so in the call log.debug(msg), log is a logger instance (of type Log). These loggers are cached and uniquely identified by name, so if two separate classes use loggers with the same name, those loggers are actually the same instance.

There are two main ways to get hold of a logger:

1. use the log instance injected into artifacts such as domain classes, controllers and services;
2. use the Commons Logging API directly.

If you use the dynamic log property, then the name of the logger is 'grails.app.<type>.<className>', where type is the type of the artifact, for example 'controller' or 'service, and className is the fully qualified name of the artifact. For example, if you have this service:

package org.example
class MyService {
    …
}

then the name of the logger will be 'grails.app.services.org.example.MyService'.

For other classes, the typical approach is to store a logger based on the class name in a constant static field:

package org.other
import org.apache.commons.logging.LogFactory
class MyClass {
    private static final log = LogFactory.getLog(this)
    …
}

This will create a logger with the name 'org.other.MyClass' - note the lack of a 'grails.app.' prefix since the class isn't an artifact. You can also pass a name to the getLog() method, such as "myLogger", but this is less common because the logging system treats names with dots ('.') in a special way.

Configuring loggers

You have already seen how to configure loggers in Grails:

log4j = {
    error  'org.codehaus.groovy.grails.web.servlet'
}

This example configures loggers with names starting with 'org.codehaus.groovy.grails.web.servlet' to ignore any messages sent to them at a level of 'warn' or lower. But is there a logger with this name in the application? No. So why have a configuration for it? Because the above rule applies to any logger whose name begins with 'org.codehaus.groovy.grails.servlet.' as well. For example, the rule applies to both the org.codehaus.groovy.grails.web.servlet.GrailsDispatcherServlet class and the org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequest one.

In other words, loggers are hierarchical. This makes configuring them by package much simpler than it would otherwise be.

The most common things that you will want to capture log output from are your controllers, services, and other artifacts. Use the convention mentioned earlier to do that: grails.app.<artifactType>.<className> . In particular the class name must be fully qualifed, i.e. with the package if there is one:

log4j = {
    // Set level for all application artifacts
    info "grails.app"
    // Set for a specific controller in the default package
    debug "grails.app.controllers.YourController"
    // Set for a specific domain class
    debug "grails.app.domain.org.example.Book"
    // Set for all taglibs
    info "grails.app.taglib"
}

The standard artifact names used in the logging configuration are:

• conf - For anything under grails-app/conf such as BootStrap.groovy (but excluding filters)
• filters - For filters
• taglib - For tag libraries
• services - For service classes
• controllers - For controllers
• domain - For domain entities

Grails itself generates plenty of logging information and it can sometimes be helpful to see that. Here are some useful loggers from Grails internals that you can use, especially when tracking down problems with your application:

• org.codehaus.groovy.grails.commons - Core artifact information such as class loading etc.
• org.codehaus.groovy.grails.web - Grails web request processing
• org.codehaus.groovy.grails.web.mapping - URL mapping debugging
• org.codehaus.groovy.grails.plugins - Log plugin activity
• grails.spring - See what Spring beans Grails and plugins are defining
• org.springframework - See what Spring is doing
• org.hibernate - See what Hibernate is doing

So far, we've only looked at explicit configuration of loggers. But what about all those loggers that don't have an explicit configuration? Are they simply ignored? The answer lies with the root logger.

The Root Logger

All logger objects inherit their configuration from the root logger, so if no explicit configuration is provided for a given logger, then any messages that go to that logger are subject to the rules defined for the root logger. In other words, the root logger provides the default configuration for the logging system.

Grails automatically configures the root logger to only handle messages at 'error' level and above, and all the messages are directed to the console (stdout for those with a C background). You can customise this behaviour by specifying a 'root' section in your logging configuration like so:

log4j = {
    root {
        info()
    }
    …
}

The above example configures the root logger to log messages at 'info' level and above to the default console appender. You can also configure the root logger to log to one or more named appenders (which we'll talk more about shortly):

log4j = {
    appenders {
        file name:'file', file:'/var/logs/mylog.log'
    }
    root {
        debug 'stdout', 'file'
    }
}

In the above example, the root logger will log to two appenders - the default 'stdout' (console) appender and a custom 'file' appender.

For power users there is an alternative syntax for configuring the root logger: the root org.apache.log4j.Logger instance is passed as an argument to the log4j closure. This lets you work with the logger directly:

log4j = { root ->
    root.level = org.apache.log4j.Level.DEBUG
    …
}

For more information on what you can do with this Logger instance, refer to the Log4j API documentation.

Those are the basics of logging pretty well covered and they are sufficient if you're happy to only send log messages to the console. But what if you want to send them to a file? How do you make sure that messages from a particular logger go to a file but not the console? These questions and more will be answered as we look into appenders.

Appenders

Loggers are a useful mechanism for filtering messages, but they don't physically write the messages anywhere. That's the job of the appender, of which there are various types. For example, there is the default one that writes messages to the console, another that writes them to a file, and several others. You can even create your own appender implementations!

This diagram shows how they fit into the logging pipeline:

As you can see, a single logger may have several appenders attached to it. In a standard Grails configuration, the console appender named 'stdout' is attached to all loggers through the default root logger configuration. But that's the only one. Adding more appenders can be done within an 'appenders' block:

log4j = {
    appenders {
        rollingFile name: "myAppender",
                    maxFileSize: 1024,
                    file: "/tmp/logs/myApp.log"
    }
}

The following appenders are available by default:

Each named argument passed to an appender maps to a property of the underlying Appender implementation. So the previous example sets the name, maxFileSize and file properties of the RollingFileAppender instance.

You can have as many appenders as you like - just make sure that they all have unique names. You can even have multiple instances of the same appender type, for example several file appenders that log to different files.

If you prefer to create the appender programmatically or if you want to use an appender implementation that's not available in the above syntax, simply declare an appender entry with an instance of the appender you want:

import org.apache.log4j.*
log4j = {
    appenders {
        appender new RollingFileAppender(
                name: "myAppender",
                maxFileSize: 1024,
                file: "/tmp/logs/myApp.log")
    }
}

This approach can be used to configure JMSAppender, SocketAppender, SMTPAppender, and more.

Once you have declared your extra appenders, you can attach them to specific loggers by passing the name as a key to one of the log level methods from the previous section:

error myAppender: "grails.app.controllers.BookController"

This will ensure that the 'grails.app.controllers.BookController' logger sends log messages to 'myAppender' as well as any appenders configured for the root logger. To add more than one appender to the logger, then add them to the same level declaration:

error myAppender:      "grails.app.controllers.BookController",
      myFileAppender:  ["grails.app.controllers.BookController",
                        "grails.app.services.BookService"],
      rollingFile:     "grails.app.controllers.BookController"

The above example also shows how you can configure more than one logger at a time for a given appender (myFileAppender) by using a list.

Be aware that you can only configure a single level for a logger, so if you tried this code:

error myAppender:      "grails.app.controllers.BookController"
debug myFileAppender:  "grails.app.controllers.BookController"
fatal rollingFile:     "grails.app.controllers.BookController"

you'd find that only 'fatal' level messages get logged for 'grails.app.controllers.BookController'. That's because the last level declared for a given logger wins. What you probably want to do is limit what level of messages an appender writes.

An appender that is attached to a logger configured with the 'all' level will generate a lot of logging information. That may be fine in a file, but it makes working at the console difficult. So we configure the console appender to only write out messages at 'info' level or above:

log4j = {
    appenders {
        console name: "stdout", threshold: org.apache.log4j.Level.INFO
    }
}

The key here is the threshold argument which determines the cut-off for log messages. This argument is available for all appenders, but do note that you currently have to specify a Level instance - a string such as "info" will not work.

Custom Layouts

By default the Log4j DSL assumes that you want to use a PatternLayout. However, there are other layouts available including:

• xml - Create an XML log file
• html - Creates an HTML log file
• simple - A simple textual log
• pattern - A Pattern layout

You can specify custom patterns to an appender using the layout setting:

log4j = {
    appenders {
        console name: "customAppender",
                layout: pattern(conversionPattern: "%c{2} %m%n")
    }
}

This also works for the built-in appender "stdout", which logs to the console:

log4j = {
    appenders {
        console name: "stdout",
                layout: pattern(conversionPattern: "%c{2} %m%n")
    }
}

Environment-specific configuration

Since the logging configuration is inside Config.groovy, you can put it inside an environment-specific block. However, there is a problem with this approach: you have to provide the full logging configuration each time you define the log4j setting. In other words, you cannot selectively override parts of the configuration - it's all or nothing.

To get around this, the logging DSL provides its own environment blocks that you can put anywhere in the configuration:

log4j = {
    appenders {
        console name: "stdout",
                layout: pattern(conversionPattern: "%c{2} %m%n")
        environments {
            production {
                rollingFile name: "myAppender", maxFileSize: 1024,
                            file: "/tmp/logs/myApp.log"
            }
        }
    }
    root {
        //…
    }
    // other shared config
    info "grails.app.controllers"
    environments {
        production {
            // Override previous setting for 'grails.app.controllers'
            error "grails.app.controllers"
        }
    }
}

The one place you can't put an environment block is inside the root definition, but you can put the root definition inside an environment block.

Full stacktraces

When exceptions occur, there can be an awful lot of noise in the stacktrace from Java and Groovy internals. Grails filters these typically irrelevant details and restricts traces to non-core Grails/Groovy class packages.

When this happens, the full trace is always logged to the StackTrace logger, which by default writes its output to a file called stacktrace.log. As with other loggers though, you can change its behaviour in the configuration. For example if you prefer full stack traces to go to the console, add this entry:

error stdout: "StackTrace"

This won't stop Grails from attempting to create the stacktrace.log file - it just redirects where stack traces are written to. An alternative approach is to change the location of the 'stacktrace' appender's file:

log4j = {
    appenders {
        rollingFile name: "stacktrace", maxFileSize: 1024,
                    file: "/var/tmp/logs/myApp-stacktrace.log"
    }
}

or, if you don't want to the 'stacktrace' appender at all, configure it as a 'null' appender:

log4j = {
    appenders {
        'null' name: "stacktrace"
    }
}

You can of course combine this with attaching the 'stdout' appender to the 'StackTrace' logger if you want all the output in the console.

Finally, you can completely disable stacktrace filtering by setting the grails.full.stacktrace VM property to true:

grails -Dgrails.full.stacktrace=true run-app

Masking Request Parameters From Stacktrace Logs

When Grails logs a stacktrace, the log message may include the names and values of all of the request parameters for the current request. To mask out the values of secure request parameters, specify the parameter names in the grails.exceptionresolver.params.exclude config property:

grails.exceptionresolver.params.exclude = ['password', 'creditCard']

Request parameter logging may be turned off altogether by setting the grails.exceptionresolver.logRequestParameters config property to false. The default value is true when the application is running in DEVELOPMENT mode and false for all other modes.

grails.exceptionresolver.logRequestParameters=false

Logger inheritance

Earlier, we mentioned that all loggers inherit from the root logger and that loggers are hierarchical based on '.'-separated terms. What this means is that unless you override a parent setting, a logger retains the level and the appenders configured for that parent. So with this configuration:

log4j = {
    appenders {
        file name:'file', file:'/var/logs/mylog.log'
    }
    root {
        debug 'stdout', 'file'
    }
}

all loggers in the application will have a level of 'debug' and will log to both the 'stdout' and 'file' appenders. What if you only want to log to 'stdout' for a particular logger? Change the 'additivity' for a logger in that case.

Additivity simply determines whether a logger inherits the configuration from its parent. If additivity is false, then its not inherited. The default for all loggers is true, i.e. they inherit the configuration. So how do you change this setting? Here's an example:

log4j = {
    appenders {
        …
    }
    root {
        …
    }
    info additivity: false
         stdout: ["grails.app.controllers.BookController",
                  "grails.app.services.BookService"]
}

So when you specify a log level, add an 'additivity' named argument. Note that you when you specify the additivity, you must configure the loggers for a named appender. The following syntax will not work:

info additivity: false, ["grails.app.controllers.BookController",
                         "grails.app.services.BookService"]

Customizing stack trace printing and filtering

Stacktraces in general and those generated when using Groovy in particular are quite verbose and contain many stack frames that aren't interesting when diagnosing problems. So Grails uses a implementation of the org.codehaus.groovy.grails.exceptions.StackTraceFilterer interface to filter out irrelevant stack frames. To customize the approach used for filtering, implement that interface in a class in src/groovy or src/java and register it in Config.groovy:

grails.logging.stackTraceFiltererClass =
         'com.yourcompany.yourapp.MyStackTraceFilterer'

In addition, Grails customizes the display of the filtered stacktrace to make the information more readable. To customize this, implement the org.codehaus.groovy.grails.exceptions.StackTracePrinter interface in a class in src/groovy or src/java and register it in Config.groovy:

grails.logging.stackTracePrinterClass =
         'com.yourcompany.yourapp.MyStackTracePrinter'

Finally, to render error information in the error GSP, an HTML-generating printer implementation is needed. The default implementation is org.codehaus.groovy.grails.web.errors.ErrorsViewStackTracePrinter and it's registered as a Spring bean. To use your own implementation, either implement the org.codehaus.groovy.grails.exceptions.StackTraceFilterer directly or subclass ErrorsViewStackTracePrinter and register it in grails-app/conf/spring/resources.groovy as:

import com.yourcompany.yourapp.MyErrorsViewStackTracePrinter
beans = {
    errorsViewStackTracePrinter(MyErrorsViewStackTracePrinter,
                                ref('grailsResourceLocator'))
}

Alternative logging libraries

By default, Grails uses Log4J to do its logging. For most people this is absolutely fine, and many users don't even care what logging library is used. But if you're not one of those and want to use an alternative, such as the JDK logging package or logback, you can do so by simply excluding a couple of dependencies from the global set and adding your own:

grails.project.dependency.resolution = {
    inherits("global") {
        excludes "grails-plugin-logging", "log4j"
    }
    …
    dependencies {
        runtime "ch.qos.logback:logback-core:0.9.29"
        …
    }
    …
}

If you do this, you will get unfiltered, standard Java stacktraces in your log files and you won't be able to use the logging configuration DSL that's just been described. Instead, you will have to use the standard configuration mechanism for the library you choose.

• grails.gorm.failOnError - If set to true, causes the save() method on domain classes to throw a grails.validation.ValidationException if validation fails during a save. This option may also be assigned a list of Strings representing package names. If the value is a list of Strings then the failOnError behavior will only be applied to domain classes in those packages (including sub-packages). See the save method docs for more information.

For example, to enable failOnError for all domain classes:

grails.gorm.failOnError=true

and to enable failOnError for domain classes by package:

grails.gorm.failOnError = ['com.companyname.somepackage',
                           'com.companyname.someotherpackage']

• grails.gorm.autoFlush = If set to true, causes the merge, save and delete methods to flush the session, replacing the need to explicitly flush using save(flush: true).

Per Environment Configuration

Grails supports the concept of per environment configuration. The Config.groovy, DataSource.groovy, and BootStrap.groovy files in the grails-app/conf directory can use per-environment configuration using the syntax provided by ConfigSlurper. As an example consider the following default DataSource definition provided by Grails:

dataSource {
    pooled = false
    driverClassName = "org.h2.Driver"
    username = "sa"
    password = ""
}
environments {
    development {
        dataSource {
            dbCreate = "create-drop"
            url = "jdbc:h2:mem:devDb"
        }
    }
    test {
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:mem:testDb"
        }
    }
    production {
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:prodDb"
        }
    }
}

Notice how the common configuration is provided at the top level and then an environments block specifies per environment settings for the dbCreate and url properties of the DataSource.

Packaging and Running for Different Environments

Grails' command line has built in capabilities to execute any command within the context of a specific environment. The format is:

grails [environment] [command name]

In addition, there are 3 preset environments known to Grails: dev, prod, and test for development, production and test. For example to create a WAR for the test environment you wound run:

grails test war

To target other environments you can pass a grails.env variable to any command:

grails -Dgrails.env=UAT run-app

Programmatic Environment Detection

Within your code, such as in a Gant script or a bootstrap class you can detect the environment using the Environment class:

import grails.util.Environment
...
switch (Environment.current) {
    case Environment.DEVELOPMENT:
        configureForDevelopment()
        break
    case Environment.PRODUCTION:
        configureForProduction()
        break
}

Per Environment Bootstrapping

Its often desirable to run code when your application starts up on a per-environment basis. To do so you can use the grails-app/conf/BootStrap.groovy file's support for per-environment execution:

def init = { ServletContext ctx ->
    environments {
        production {
            ctx.setAttribute("env", "prod")
        }
        development {
            ctx.setAttribute("env", "dev")
        }
    }
    ctx.setAttribute("foo", "bar")
}

Generic Per Environment Execution

The previous BootStrap example uses the grails.util.Environment class internally to execute. You can also use this class yourself to execute your own environment specific logic:

Environment.executeForCurrentEnvironment {
    production {
        // do something in production
    }
    development {
        // do something only in development
    }
}

If you use a database other than H2 you need a JDBC driver. For example for MySQL you would need Connector/J

Drivers typically come in the form of a JAR archive. It's best to use Ivy to resolve the jar if it's available in a Maven repository, for example you could add a dependency for the MySQL driver like this:

grails.project.dependency.resolution = {
    inherits("global")
    log "warn"
    repositories {
        grailsPlugins()
        grailsHome()
        grailsCentral()
        mavenCentral()
    }
    dependencies {
        runtime 'mysql:mysql-connector-java:5.1.16'
    }
}

Note that the built-in mavenCentral() repository is included here since that's a reliable location for this library.

If you can't use Ivy then just put the JAR in your project's lib directory.

Once you have the JAR resolved you need to get familiar Grails' DataSource descriptor file located at grails-app/conf/DataSource.groovy. This file contains the dataSource definition which includes the following settings:

• driverClassName - The class name of the JDBC driver
• username - The username used to establish a JDBC connection
• password - The password used to establish a JDBC connection
• url - The JDBC URL of the database
• dbCreate - Whether to auto-generate the database from the domain model - one of 'create-drop', 'create', 'update' or 'validate'
• pooled - Whether to use a pool of connections (defaults to true)
• logSql - Enable SQL logging to stdout
• formatSql - Format logged SQL
• dialect - A String or Class that represents the Hibernate dialect used to communicate with the database. See the org.hibernate.dialect package for available dialects.
• readOnly - If true makes the DataSource read-only, which results in the connection pool calling setReadOnly(true) on each Connection
• properties - Extra properties to set on the DataSource bean. See the Commons DBCP BasicDataSource documentation.

A typical configuration for MySQL may be something like:

dataSource {
    pooled = true
    dbCreate = "update"
    url = "jdbc:mysql://localhost/yourDB"
    driverClassName = "com.mysql.jdbc.Driver"
    dialect = org.hibernate.dialect.MySQL5InnoDBDialect
    username = "yourUser"
    password = "yourPassword"
}

When configuring the DataSource do not include the type or the def keyword before any of the configuration settings as Groovy will treat these as local variable definitions and they will not be processed. For example the following is invalid:

dataSource {
    boolean pooled = true // type declaration results in ignored local variable
    …
}

Example of advanced configuration using extra properties:

dataSource {
    pooled = true
    dbCreate = "update"
    url = "jdbc:mysql://localhost/yourDB"
    driverClassName = "com.mysql.jdbc.Driver"
    dialect = org.hibernate.dialect.MySQL5InnoDBDialect
    username = "yourUser"
    password = "yourPassword"
    properties {
        maxActive = 50
        maxIdle = 25
        minIdle = 5
        initialSize = 5
        minEvictableIdleTimeMillis = 60000
        timeBetweenEvictionRunsMillis = 60000
        maxWait = 10000
        validationQuery = "/* ping */"
    }
}

More on dbCreate

Hibernate can automatically create the database tables required for your domain model. You have some control over when and how it does this through the dbCreate property, which can take these values:

• create - Drops the existing schemaCreates the schema on startup, dropping existing tables, indexes, etc. first.
• create-drop - Same as create, but also drops the tables when the application shuts down cleanly.
• update - Creates missing tables and indexes, and updates the current schema without dropping any tables or data. Note that this can't properly handle many schema changes like column renames (you're left with the old column containing the existing data).
• validate - Makes no changes to your database. Compares the configuration with the existing database schema and reports warnings.
• any other value - does nothing

You can also remove the dbCreate setting completely, which is recommended once your schema is relatively stable and definitely when your application and database are deployed in production. Database changes are then managed through proper migrations, either with SQL scripts or a migration tool like Liquibase (the Database Migration plugin uses Liquibase and is tightly integrated with Grails and GORM).

Grails' DataSource definition is "environment aware", however, so you can do:

dataSource {
    pooled = true
    driverClassName = "com.mysql.jdbc.Driver"
    dialect = org.hibernate.dialect.MySQL5InnoDBDialect
    // other common settings here
}
environments {
    production {
        dataSource {
            url = "jdbc:mysql://liveip.com/liveDb"
            // other environment-specific settings here
        }
    }
}

Referring to a JNDI DataSource

Most Java EE containers supply DataSource instances via Java Naming and Directory Interface (JNDI). Grails supports the definition of JNDI data sources as follows:

dataSource {
    jndiName = "java:comp/env/myDataSource"
}

The format on the JNDI name may vary from container to container, but the way you define the DataSource in Grails remains the same.

Configuring a Development time JNDI resource

The way in which you configure JNDI data sources at development time is plugin dependent. Using the Tomcat plugin you can define JNDI resources using the grails.naming.entries setting in grails-app/conf/Config.groovy:

grails.naming.entries = [
    "bean/MyBeanFactory": [
        auth: "Container",
        type: "com.mycompany.MyBean",
        factory: "org.apache.naming.factory.BeanFactory",
        bar: "23"
    ],
    "jdbc/EmployeeDB": [
        type: "javax.sql.DataSource", //required
        auth: "Container", // optional
        description: "Data source for Foo", //optional
        driverClassName: "org.h2.Driver",
        url: "jdbc:h2:mem:database",
        username: "dbusername",
        password: "dbpassword",
        maxActive: "8",
        maxIdle: "4"
    ],
    "mail/session": [
        type: "javax.mail.Session,
        auth: "Container",
        "mail.smtp.host": "localhost"
    ]
]

• create
• create-drop
• update
• validate
• no value

In development mode dbCreate is by default set to "create-drop", but at some point in development (and certainly once you go to production) you'll need to stop dropping and re-creating the database every time you start up your server.

It's tempting to switch to update so you retain existing data and only update the schema when your code changes, but Hibernate's update support is very conservative. It won't make any changes that could result in data loss, and doesn't detect renamed columns or tables, so you'll be left with the old one and will also have the new one.

Grails supports Rails-style migrations via the Database Migration plugin which can be installed by running

grails install-plugin database-migration

The plugin uses Liquibase and and provides access to all of its functionality, and also has support for GORM (for example generating a change set by comparing your domain classes to a database).

If this were not the case, then retrieving a connection from the dataSource would be a new connection, and you wouldn't be able to see changes that haven't been committed yet (assuming you have a sensible transaction isolation setting, e.g. READ_COMMITTED or better).

The "real" unproxied dataSource is still available to you if you need access to it; its bean name is dataSourceUnproxied.

You can access this bean like any other Spring bean, i.e. using dependency injection:

class MyService {
   def dataSourceUnproxied
   …
}

or by pulling it from the ApplicationContext:

def dataSourceUnproxied = ctx.dataSourceUnproxied

You can access the console by navigating to http://localhost:8080/appname/dbconsole in a browser. The URI can be configured using the grails.dbconsole.urlRoot attribute in Config.groovy and defaults to '/dbconsole'.

The console is enabled by default in development mode and can be disabled or enabled in other environments by using the grails.dbconsole.enabled attribute in Config.groovy. For example you could enable the console in production using

environments {
    production {
        grails.serverURL = "http://www.changeme.com"
        grails.dbconsole.enabled = true
        grails.dbconsole.urlRoot = '/admin/dbconsole'
    }
    development {
        grails.serverURL = "http://localhost:8080/${appName}"
    }
    test {
        grails.serverURL = "http://localhost:8080/${appName}"
    }
}

If you enable the console in production be sure to guard access to it using a trusted security framework.

Configuration

By default the console is configured for an H2 database which will work with the default settings if you haven't configured an external database - you just need to change the JDBC URL to jdbc:h2:mem:devDB. If you've configured an external database (e.g. MySQL, Oracle, etc.) then you can use the Saved Settings dropdown to choose a settings template and fill in the url and username/password information from your DataSource.groovy.

Configuring Additional DataSources

The default DataSource configuration in grails-app/conf/DataSource.groovy looks something like this:

dataSource {
    pooled = true
    driverClassName = "org.h2.Driver"
    username = "sa"
    password = ""
}
hibernate {
    cache.use_second_level_cache = true
    cache.use_query_cache = true
    cache.provider_class = 'net.sf.ehcache.hibernate.EhCacheProvider'
}
environments {
    development {
        dataSource {
            dbCreate = "create-drop"
            url = "jdbc:h2:mem:devDb"
        }
    }
    test {
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:mem:testDb"
        }
    }
    production {
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:prodDb"
        }
    }
}

This configures a single DataSource with the Spring bean named dataSource. To configure extra DataSources, add another dataSource block (at the top level, in an environment block, or both, just like the standard DataSource definition) with a custom name, separated by an underscore. For example, this configuration adds a second DataSource, using MySQL in the development environment and Oracle in production:

environments {
    development {
        dataSource {
            dbCreate = "create-drop"
            url = "jdbc:h2:mem:devDb"
        }
        dataSource_lookup {
            dialect = org.hibernate.dialect.MySQLInnoDBDialect
            driverClassName = 'com.mysql.jdbc.Driver'
            username = 'lookup'
            password = 'secret'
            url = 'jdbc:mysql://localhost/lookup'
            dbCreate = 'update'
        }
    }
    test {
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:mem:testDb"
        }
    }
    production {
        dataSource {
            dbCreate = "update"
            url = "jdbc:h2:prodDb"
        }
        dataSource_lookup {
            dialect = org.hibernate.dialect.Oracle10gDialect
            driverClassName = 'oracle.jdbc.driver.OracleDriver'
            username = 'lookup'
            password = 'secret'
            url = 'jdbc:oracle:thin:@localhost:1521:lookup'
            dbCreate = 'update'
        }
    }
}

You can use the same or different databases as long as they're supported by Hibernate.

Configuring Domain Classes

If a domain class has no DataSource configuration, it defaults to the standard 'dataSource'. Set the datasource property in the mapping block to configure a non-default DataSource. For example, if you want to use the ZipCode domain to use the 'lookup' DataSource, configure it like this;

class ZipCode {
   String code
   static mapping = {
      datasource 'lookup'
   }
}

A domain class can also use two or more DataSources. Use the datasources property with a list of names to configure more than one, for example:

class ZipCode {
   String code
   static mapping = {
      datasources(['lookup', 'auditing'])
   }
}

If a domain class uses the default DataSource and one or more others, use the special name 'DEFAULT' to indicate the default DataSource:

class ZipCode {
   String code
   static mapping = {
      datasources(['lookup', 'DEFAULT'])
   }
}

If a domain class uses all configured DataSources use the special value 'ALL':

class ZipCode {
   String code
   static mapping = {
      datasource 'ALL'
   }
}

Namespaces and GORM Methods

If a domain class uses more than one DataSource then you can use the namespace implied by each DataSource name to make GORM calls for a particular DataSource. For example, consider this class which uses two DataSources:

class ZipCode {
   String code
   static mapping = {
      datasources(['lookup', 'auditing'])
   }
}

The first DataSource specified is the default when not using an explicit namespace, so in this case we default to 'lookup'. But you can call GORM methods on the 'auditing' DataSource with the DataSource name, for example:

def zipCode = ZipCode.auditing.get(42)
…
zipCode.auditing.save()

As you can see, you add the DataSource to the method call in both the static case and the instance case.

Services

Like Domain classes, by default Services use the default DataSource and PlatformTransactionManager. To configure a Service to use a different DataSource, use the static datasource property, for example:

class DataService {
   static datasource = 'lookup'
   void someMethod(...) {
      …
   }
}

A transactional service can only use a single DataSource, so be sure to only make changes for domain classes whose DataSource is the same as the Service.

Note that the datasource specified in a service has no bearing on which datasources are used for domain classes; that's determined by their declared datasources in the domain classes themselves. It's used to declare which transaction manager to use.

What you'll see is that if you have a Foo domain class in dataSource1 and a Bar domain class in dataSource2, and WahooService uses dataSource1, a service method that saves a new Foo and a new Bar will only be transactional for Foo since they share the datasource. The transaction won't affect the Bar instance. If you want both to be transactional you'd need to use two services and XA datasources for two-phase commit, e.g. with the Atomikos plugin.

XA and Two-phase Commit

Grails has no native support for XA DataSources or two-phase commit, but the Atomikos plugin makes it easy. See the plugin documentation for the simple changes needed in your DataSource definitions to reconfigure them as XA DataSources.

grails.config.locations = [
    "classpath:${appName}-config.properties",
    "classpath:${appName}-config.groovy",
    "file:${userHome}/.grails/${appName}-config.properties",
    "file:${userHome}/.grails/${appName}-config.groovy" ]

In the above example we're loading configuration files (both Java Properties files and ConfigSlurper configurations) from different places on the classpath and files located in USER_HOME.

It is also possible to load config by specifying a class that is a config script.

grails.config.locations = [com.my.app.MyConfig]

This can be useful in situations where the config is either coming from a plugin or some other part of your application. A typical use for this is re-using configuration provided by plugins across multiple applications.

Ultimately all configuration files get merged into the config property of the GrailsApplication object and are hence obtainable from there.

Values that have the same name as previously defined values will overwrite the existing values, and the pointed to configuration sources are loaded in the order in which they are defined.

Config Defaults

The configuration values contained in the locations described by the grails.config.locations property will override any values defined in your application Config.groovy file which may not be what you want. You may want to have a set of default values be be loaded that can be overridden in either your application's Config.groovy file or in a named config location. For this you can use the grails.config.defaults.locations property.

This property supports the same values as the grails.config.locations property (i.e. paths to config scripts, property files or classes), but the config described by grails.config.defaults.locations will be loaded before all other values and can therefore be overridden. Some plugins use this mechanism to supply one or more sets of default configuration that you can choose to include in your application config.

Grails also supports the concept of property place holders and property override configurers as defined in Spring For more information on these see the section on Grails and Spring

Versioning Basics

Grails has built in support for application versioning. The version of the application is set to 0.1 when you first create an application with the create-app command. The version is stored in the application meta data file application.properties in the root of the project.

To change the version of your application you can edit the file manually, or run the set-version command:

grails set-version 0.2

The version is used in various commands including the war command which will append the application version to the end of the created WAR file.

Detecting Versions at Runtime

You can detect the application version using Grails' support for application metadata using the GrailsApplication class. For example within controllers there is an implicit grailsApplication variable that can be used:

def version = grailsApplication.metadata['app.version']

You can retrieve the the version of Grails that is running with:

def grailsVersion = grailsApplication.metadata['app.grails.version']

or the GrailsUtil class:

import grails.util.GrailsUtil
…
def grailsVersion = GrailsUtil.grailsVersion

The documentation engine uses a variation on the Textile syntax to automatically create project documentation with smart linking, formatting etc.

Creating project documentation

To use the engine you need to follow a few conventions. First, you need to create a src/docs/guide directory where your documentation source files will go. Then, you need to create the source docs themselves. Each chapter should have its own gdoc file as should all numbered sub-sections. You will end up with something like:

+ src/docs/guide/introduction.gdoc
+ src/docs/guide/introduction/changes.gdoc
+ src/docs/guide/gettingStarted.gdoc
+ src/docs/guide/configuration.gdoc
+ src/docs/guide/configuration/build.gdoc
+ src/docs/guide/configuration/build/controllers.gdoc

Note that you can have all your gdoc files in the top-level directory if you want, but you can also put sub-sections in sub-directories named after the parent section - as the above example shows.

Once you have your source files, you still need to tell the documentation engine what the structure of your user guide is going to be. To do that, you add a src/docs/guide/toc.yml file that contains the structure and titles for each section. This file is in YAML format and basically represents the structure of the user guide in tree form. For example, the above files could be represented as:

introduction:
  title: Introduction
  changes: Change Log
gettingStarted: Getting Started
configuration:
  title: Configuration
  build:
    title: Build Config
    controllers: Specifying Controllers

The format is pretty straightforward. Any section that has sub-sections is represented with the corresponding filename (minus the .gdoc extension) followed by a colon. The next line should contain title: plus the title of the section as seen by the end user. Every sub-section then has its own line after the title. Leaf nodes, i.e. those without any sub-sections, declare their title on the same line as the section name but after the colon.

That's it. You can easily add, remove, and move sections within the toc.yml to restructure the generated user guide. You should also make sure that all section names, i.e. the gdoc filenames, should be unique since they are used for creating internal links and for the HTML filenames. Don't worry though, the documentation engine will warn you of duplicate section names.

Creating reference items

Reference items appear in the Quick Reference section of the documentation. Each reference item belongs to a category and a category is a directory located in the src/docs/ref directory. For example, suppose you have defined a new controller method called renderPDF. That belongs to the Controllers category so you would create a gdoc text file at the following location:

+ src/docs/ref/Controllers/renderPDF.gdoc

Configuring Output Properties

There are various properties you can set within your grails-app/conf/Config.groovy file that customize the output of the documentation such as:

• grails.doc.title - The title of the documentation
• grails.doc.subtitle - The subtitle of the documentation
• grails.doc.authors - The authors of the documentation
• grails.doc.license - The license of the software
• grails.doc.copyright - The copyright message to display
• grails.doc.footer - The footer to use

Other properties such as the version are pulled from your project itself. If a title is not specified, the application name is used.

Generating Documentation

Once you have created some documentation (refer to the syntax guide in the next chapter) you can generate an HTML version of the documentation using the command:

grails doc

This command will output an docs/manual/index.html which can be opened in a browser to view your documentation.

Documentation Syntax

As mentioned the syntax is largely similar to Textile or Confluence style wiki markup. The following sections walk you through the syntax basics.

Basic Formatting

Monospace: monospace

@monospace@

Italic: italic

_italic_

Bold: bold

*bold*

Image:

!http://grails.org/images/new/grailslogo_topNav.png!

Linking

There are several ways to create links with the documentation generator. A basic external link can either be defined using confluence or textile style markup:

[SpringSource|http://www.springsource.com/]

or

"SpringSource":http://www.springsource.com/

For links to other sections inside the user guide you can use the guide: prefix with the name of the section you want to link to:

[Intro|guide:introduction]

The section name comes from the corresponding gdoc filename. The documentation engine will warn you if any links to sections in your guide break.

To link to reference items you can use a special syntax:

[controllers|renderPDF]

In this case the category of the reference item is on the left hand side of the | and the name of the reference item on the right.

Finally, to link to external APIs you can use the api: prefix. For example:

[String|api:java.lang.String]

The documentation engine will automatically create the appropriate javadoc link in this case. To add additional APIs to the engine you can configure them in grails-app/conf/Config.groovy. For example:

grails.doc.api.org.hibernate=
            "http://docs.jboss.org/hibernate/stable/core/javadocs"

The above example configures classes within the org.hibernate package to link to the Hibernate website's API docs.

Lists and Headings

Headings can be created by specifying the letter 'h' followed by a number and then a dot:

h3.<space>Heading3
h4.<space>Heading4

Unordered lists are defined with the use of the * character:

* item 1
** subitem 1
** subitem 2
* item 2

Numbered lists can be defined with the # character:

# item 1

Tables can be created using the table macro:

{table}
 *Name* | *Number*
 Albert | 46
 Wilma | 1348
 James | 12
{table}

Code and Notes

You can define code blocks with the code macro:

class Book {
    String title
}

{code}
class Book {
    String title
}
{code}

The example above provides syntax highlighting for Java and Groovy code, but you can also highlight XML markup:

<hello>world</hello>

{code:xml}
<hello>world</hello>
{code}

There are also a couple of macros for displaying notes and warnings:

Note:

This is a note!

{note}
This is a note!
{note}

Warning:

This is a warning!

{warning}
This is a warning!
{warning}

You specify a grails.project.dependency.resolution property inside the grails-app/conf/BuildConfig.groovy file that configures how dependencies are resolved:

grails.project.dependency.resolution = {
   // config here
}

The default configuration looks like the following:

grails.project.class.dir = "target/classes"
grails.project.test.class.dir = "target/test-classes"
grails.project.test.reports.dir = "target/test-reports"
//grails.project.war.file = "target/${appName}-${appVersion}.war"
grails.project.dependency.resolution = {
    // inherit Grails' default dependencies
    inherits("global") {
        // uncomment to disable ehcache
        // excludes 'ehcache'
    }
    log "warn"
    repositories {
        grailsPlugins()
        grailsHome()
        grailsCentral()
        // uncomment these to enable remote dependency resolution
        // from public Maven repositories
        //mavenCentral()
        //mavenLocal()
        //mavenRepo "http://snapshots.repository.codehaus.org"
        //mavenRepo "http://repository.codehaus.org"
        //mavenRepo "http://download.java.net/maven/2/"
        //mavenRepo "http://repository.jboss.com/maven2/"
    }
    dependencies {
        // specify dependencies here under either 'build', 'compile',
        // 'runtime', 'test' or 'provided' scopes eg.
        // runtime 'mysql:mysql-connector-java:5.1.16'
    }
    plugins {
        compile ":hibernate:$grailsVersion"
        compile ":jquery:1.6.1.1"
        compile ":resources:1.0"
        build ":tomcat:$grailsVersion"
    }
}

The details of the above will be explained in the next few sections.

• build: Dependencies for the build system only
• compile: Dependencies for the compile step
• runtime: Dependencies needed at runtime but not for compilation (see above)
• test: Dependencies needed for testing but not at runtime (see above)
• provided: Dependencies needed at development time, but not during WAR deployment

Within the dependencies block you can specify a dependency that falls into one of these configurations by calling the equivalent method. For example if your application requires the MySQL driver to function at runtime you can specify that like this:

runtime 'com.mysql:mysql-connector-java:5.1.16'

This uses the string syntax: group:name:version. You can also use a Map-based syntax:

runtime group: 'com.mysql',
        name: 'mysql-connector-java',
        version: '5.1.16'

In Maven terminology, group corresponds to an artifact's groupId and name corresponds to its artifactId.

Multiple dependencies can be specified by passing multiple arguments:

runtime 'com.mysql:mysql-connector-java:5.1.16',
        'net.sf.ehcache:ehcache:1.6.1'
// Or
runtime(
    [group:'com.mysql', name:'mysql-connector-java', version:'5.1.16'],
    [group:'net.sf.ehcache', name:'ehcache', version:'1.6.1']
)

Disabling transitive dependency resolution

By default, Grails will not only get the JARs and plugins that you declare, but it will also get their transitive dependencies. This is usually what you want, but there are occasions where you want a dependency without all its baggage. In such cases, you can disable transitive dependency resolution on a case-by-case basis:

runtime('com.mysql:mysql-connector-java:5.1.16',
        'net.sf.ehcache:ehcache:1.6.1') {
    transitive = false
}
// Or
runtime group:'com.mysql',
        name:'mysql-connector-java',
        version:'5.1.16',
        transitive:false

Excluding specific transitive dependencies

A far more common scenario is where you want the transitive dependencies, but some of them cause issues with your own dependencies or are unnecessary. For example, many Apache projects have 'commons-logging' as a transitive dependency, but it shouldn't be included in a Grails project (we use SLF4J). That's where the excludes option comes in:

runtime('com.mysql:mysql-connector-java:5.1.16',
        'net.sf.ehcache:ehcache:1.6.1') {
    excludes "xml-apis", "commons-logging"
}
// Or
runtime(group:'com.mysql', name:'mysql-connector-java', version:'5.1.16') {
    excludes([ group: 'xml-apis', name: 'xml-apis'],
             [ group: 'org.apache.httpcomponents' ],
             [ name: 'commons-logging' ])

As you can see, you can either exclude dependencies by their artifact ID (also known as a module name) or any combination of group and artifact IDs (if you use the Map notation). You may also come across exclude as well, but that can only accept a single string or Map:

runtime('com.mysql:mysql-connector-java:5.1.16',
        'net.sf.ehcache:ehcache:1.6.1') {
    exclude "xml-apis"
}

Using Ivy module configurations

If you use Ivy module configurations and wish to depend on a specific configuration of a module, you can use the dependencyConfiguration method to specify the configuration to use.

provided("my.org:web-service:1.0") {
    dependencyConfiguration "api"
}

If the dependency configuration is not explicitly set, the configuration named "default" will be used (which is also the correct value for dependencies coming from Maven style repositories).

Where are the JARs?

With all these declarative dependencies, you may wonder where all the JARs end up. They have to go somewhere after all. By default Grails puts them into a directory, called the dependency cache, that resides on your local file system at user.home/.grails/ivy-cache. You can change this either via the settings.groovy file:

grails.dependency.cache.dir = "${userHome}/.my-dependency-cache"

or in the dependency DSL:

grails.project.dependency.resolution = {
    …
    cacheDir "target/ivy-cache"
    …
}

The settings.groovy option applies to all projects, so it's the preferred approach.

Remote Repositories

Initially your BuildConfig.groovy does not use any remote public Maven repositories. There is a default grailsHome() repository that will locate the JAR files Grails needs from your Grails installation. To use a public repository, specify it in the repositories block:

repositories {
    mavenCentral()
}

In this case the default public Maven repository is specified. To use the SpringSource Enterprise Bundle Repository you can use the ebr() method:

repositories {
    ebr()
}

You can also specify a specific Maven repository to use by URL:

repositories {
    mavenRepo "http://repository.codehaus.org"
}

and even give it a name:

repositories {
    mavenRepo name: "Codehaus", root: "http://repository.codehaus.org"
}

so that you can easily identify it in logs.

Controlling Repositories Inherited from Plugins

A plugin you have installed may define a reference to a remote repository just as an application can. By default your application will inherit this repository definition when you install the plugin.

If you do not wish to inherit repository definitions from plugins then you can disable repository inheritance:

repositories {
    inherit false
}

In this case your application will not inherit any repository definitions from plugins and it is down to you to provide appropriate (possibly internal) repository definitions.

Offline Mode

There are times when it is not desirable to connect to any remote repositories (whilst working on the train for example!). In this case you can use the offline flag to execute Grails commands and Grails will not connect to any remote repositories:

grails --offline run-app

Note that this command will fail if you do not have the necessary dependencies in your local Ivy cache

You can also globally configure offline mode by setting grails.offline.mode to true in ~/.grails/settings.groovy or in your project's BuildConfig.groovy file:

grails.offline.mode=true

Local Resolvers

If you do not wish to use a public Maven repository you can specify a flat file repository:

repositories {
    flatDir name:'myRepo', dirs:'/path/to/repo'
}

To specify your local Maven cache (~/.m2/repository) as a repository:

repositories {
    mavenLocal()
}

Custom Resolvers

If all else fails since Grails builds on Apache Ivy you can specify an Ivy resolver:

/*
 * Configure our resolver.
 */
def libResolver = new org.apache.ivy.plugins.resolver.URLResolver()
['libraries', 'builds'].each {
    libResolver.addArtifactPattern(
            "http://my.repository/${it}/" +
            "[organisation]/[module]/[revision]/[type]s/[artifact].[ext]")
    libResolver.addIvyPattern(
            "http://my.repository/${it}/" +
            "[organisation]/[module]/[revision]/[type]s/[artifact].[ext]")
}
libResolver.name = "my-repository"
libResolver.settings = ivySettings
resolver libResolver

It's also possible to pull dependencies from a repository using SSH. Ivy comes with a dedicated resolver that you can configure and include in your project like so:

import org.apache.ivy.plugins.resolver.SshResolver
…
repositories {
    ...
    def sshResolver = new SshResolver(
            name: "myRepo",
            user: "username",
            host: "dev.x.com",
            keyFile: new File("/home/username/.ssh/id_rsa"),
            m2compatible: true)
    sshResolver.addArtifactPattern(
            "/home/grails/repo/[organisation]/[artifact]/" +
            "[revision]/[artifact]-[revision].[ext]")
    sshResolver.latestStrategy =
            new org.apache.ivy.plugins.latest.LatestTimeStrategy()
    sshResolver.changingPattern = ".*SNAPSHOT"
    sshResolver.setCheckmodified(true)
    resolver sshResolver
}

Download the JSch JAR and add it to Grails' classpath to use the SSH resolver. You can do this by passing the path in the Grails command line:

grails -classpath /path/to/jsch compile|run-app|etc.

You can also add its path to the CLASSPATH environment variable but be aware this it affects many Java applications. An alternative on Unix is to create an alias for grails -classpath ... so that you don't have to type the extra arguments each time.

Authentication

If your repository requires authentication you can configure this using a credentials block:

credentials {
    realm = ".."
    host = "localhost"
    username = "myuser"
    password = "mypass"
}

This can be placed in your USER_HOME/.grails/settings.groovy file using the grails.project.ivy.authentication setting:

grails.project.ivy.authentication = {
    credentials {
        realm = ".."
        host = "localhost"
        username = "myuser"
        password = "mypass"
    }
}

// log level of Ivy resolver, either 'error', 'warn',
// 'info', 'debug' or 'verbose'
log "warn"

A common issue is that the checksums for a dependency don't match the associated JAR file, and so Ivy rejects the dependency. This helps ensure that the dependencies are valid. But for a variety of reasons some dependencies simply don't have valid checksums in the repositories, even if they are valid JARs. To get round this, you can disable Ivy's dependency checks like so:

grails.project.dependency.resolution = {
    …
    log "warn"
    checksums false
    …
}

This is a global setting, so only use it if you have to.

inherits "global"

Inside the BuildConfig.groovy file. To exclude specific inherited dependencies you use the excludes method:

inherits("global") {
    excludes "oscache", "ehcache"
}

The dependency resolution DSL provides a mechanism to express that all of the default dependencies will be provided by the container. This is done by invoking the defaultDependenciesProvided method and passing true as an argument:

grails.project.dependency.resolution = {
    defaultDependenciesProvided true // all of the default dependencies will
                                     // be "provided" by the container
    inherits "global" // inherit Grails' default dependencies
    repositories {
        grailsHome()
        …
    }
    dependencies {
        …
    }
}

defaultDependenciesProvided must come before inherits, otherwise the Grails dependencies will be included in the war.

Whenever you have a changing dependency, Grails will always check the remote repository for a new version. More specifically, when a changing dependency is encountered during dependency resolution its last modified timestamp in the local cache is compared against the last modified timestamp in the dependency repositories. If the version on the remote server is deemed to be newer than the version in the local cache, the new version will be downloaded and used.

{info} Be sure to read the next section on “Dependency Resolution Caching” in addition to this one as it affects changing dependencies. {info}

All dependencies (jars and plugins) with a version number ending in -SNAPSHOT are implicitly considered to be changing by Grails. You can also explicitly specify that a dependency is changing by setting the changing flag in the dependency DSL:

runtime ('org.my:lib:1.2.3') {
    changing = true
}

There is a caveat to the support for changing dependencies that you should be aware of. Grails will stop looking for newer versions of a dependency once it finds a remote repository that has the dependency.

Consider the following setup:

grails.project.dependency.resolution = {
    repositories {
        mavenLocal()
        mavenRepo "http://my.org/repo"
    }
    dependencies {
        compile "myorg:mylib:1.0-SNAPSHOT"
    }

In this example we are using the local maven repository and a remote network maven repository. Assuming that the local Grails dependency and the local Maven cache do not contain the dependency but the remote repository does, when we perform dependency resolution the following actions will occur:

• maven local repository is searched, dependency not found
• maven network repository is searched, dependency is downloaded to the cache and used

Note that the repositories are checked in the order they are defined in the BuildConfig.groovy file.

If we perform dependency resolution again without the dependency changing on the remote server, the following will happen:

• maven local repository is searched, dependency not found
• maven network repository is searched, dependency is found to be the same “age” as the version in the cache so will not be updated (i.e. downloaded)

Later on, a new version of mylib 1.0-SNAPSHOT is published changing the version on the server. The next time we perform dependency resolution, the following will happen:

• maven local repository is searched, dependency not found
• maven network repository is searched, dependency is found to newer than version in the cache so will be updated (i.e. downloaded to the cache)

So far everything is working well.

Now we want to test some local changes to the mylib library. To do this we build it locally and install it to the local Maven cache (how doesn't particularly matter). The next time we perform a dependency resolution, the following will occur:

• maven local repository is searched, dependency is found to newer than version in the cache so will be updated (i.e. downloaded to the cache)
• maven network repository is NOT searched as we've already found the dependency

This is what we wanted to occur.

Later on, a new version of mylib 1.0-SNAPSHOT is published changing the version on the server. The next time we perform dependency resolution, the following will happen:

• maven local repository is searched, dependency is found to be the same “age” as the version in the cache so will not be updated (i.e. downloaded)
• maven network repository is NOT searched as we've already found the dependency

This is likely to not be the desired outcome. We are now out of sync with the latest published snapshot and will continue to keep using the version from the local maven repository.

The rule to remember is this: when resolving a dependency, Grails will stop searching as soon as it finds a repository that has the dependency at the specified version number. It will not continue searching all repositories trying to find a more recently modified instance.

To remedy this situation (i.e. build against the newer version of mylib 1.0-SNAPSHOT in the remote repository), you can either:

• Delete the version from the local maven repository, or
• Reorder the repositories in the BuildConfig.groovy file

Where possible, prefer deleting the version from the local maven repository. In general, when you have finished building against a locally built SNAPSHOT always try to clear it from the local maven repository.

This changing dependency behaviour is an unmodifiable characteristic of the underlying dependency management system that Grails uses, Apache Ivy. It is currently not possible to have Ivy search all repositories to look for newer versions (in terms of modification date) of the same dependency (i.e. the same combination of group, name and version).

To obtain a report of an application's dependencies you can run the dependency-report command:

grails dependency-report

By default this will generate reports in the target/dependency-report directory. You can specify which configuration (scope) you want a report for by passing an argument containing the configuration name:

grails dependency-report runtime

Specifying Plugin JAR dependencies

The way in which you specify dependencies for a plugin is identical to how you specify dependencies in an application. When a plugin is installed into an application the application automatically inherits the dependencies of the plugin.

To define a dependency that is resolved for use with the plugin but not exported to the application then you can set the export property of the dependency:

test('org.spockframework:spock-core:0.5-groovy-1.8') {
    export = false
}

In this case the Spock dependency will be available only to the plugin and not resolved as an application dependency. Alternatively, if you're using the Map syntax:

test group: 'org.spockframework', name: 'spock-core',
     version: '0.5-groovy-1.8', export: false

You can use exported = false instead of export = false, but we recommend the latter because it's consistent with the Map argument.

Overriding Plugin JAR Dependencies in Your Application

If a plugin is using a JAR which conflicts with another plugin, or an application dependency then you can override how a plugin resolves its dependencies inside an application using exclusions. For example:

plugins {
    compile(":hibernate:$grailsVersion") {
        excludes "javassist"
    }
}
dependencies {
    runtime "javassist:javassist:3.4.GA"
}

In this case the application explicitly declares a dependency on the "hibernate" plugin and specifies an exclusion using the excludes method, effectively excluding the javassist library as a dependency.

However, if you would like to continue using Grails regular commands like run-app, test-app and so on then you can tell Grails' command line to load dependencies from the Maven pom.xml file instead.

To do so simply add the following line to your BuildConfig.groovy:

grails.project.dependency.resolution = {
    pom true
    ..
}

The line pom true tells Grails to parse Maven's pom.xml and load dependencies from there.

The plugin provides the ability to publish Grails projects and plugins to local and remote Maven repositories. There are two key additional targets added by the plugin:

• maven-install - Installs a Grails project or plugin into your local Maven cache
• maven-deploy - Deploys a Grails project or plugin to a remote Maven repository

By default this plugin will automatically generate a valid pom.xml for you unless a pom.xml is already present in the root of the project, in which case this pom.xml file will be used.

maven-install

The maven-install command will install the Grails project or plugin artifact into your local Maven cache:

grails maven-install

In the case of plugins, the plugin zip file will be installed, whilst for application the application WAR file will be installed.

maven-deploy

The maven-deploy command will deploy a Grails project or plugin into a remote Maven repository:

grails maven-deploy

It is assumed that you have specified the necessary <distributionManagement> configuration within a pom.xml or that you specify the id of the remote repository to deploy to:

grails maven-deploy --repository=myRepo

The repository argument specifies the 'id' for the repository. Configure the details of the repository specified by this 'id' within your grails-app/conf/BuildConfig.groovy file or in your $USER_HOME/.grails/settings.groovy file:

grails.project.dependency.distribution = {
    localRepository = "/path/to/my/local"
    remoteRepository(id: "myRepo", url: "http://myserver/path/to/repo")
}

The syntax for configuring remote repositories matches the syntax from the remoteRepository element in the Ant Maven tasks. For example the following XML:

<remoteRepository id="myRepo" url="scp://localhost/www/repository">
    <authentication username="..." privateKey="${user.home}/.ssh/id_dsa"/>
</remoteRepository>

Can be expressed as:

remoteRepository(id: "myRepo", url: "scp://localhost/www/repository") {
    authentication username: "...", privateKey: "${userHome}/.ssh/id_dsa"
}

By default the plugin will try to detect the protocol to use from the URL of the repository (ie "http" from "http://.." etc.), however to specify a different protocol you can do:

grails maven-deploy --repository=myRepo --protocol=webdav

The available protocols are:

• http
• scp
• scpexe
• ftp
• webdav

Groups, Artifacts and Versions

Maven defines the notion of a 'groupId', 'artifactId' and a 'version'. This plugin pulls this information from the Grails project conventions or plugin descriptor.

Projects

For applications this plugin will use the Grails application name and version provided by Grails when generating the pom.xml file. To change the version you can run the set-version command:

grails set-version 0.2

The Maven groupId will be the same as the project name, unless you specify a different one in Config.groovy:

grails.project.groupId="com.mycompany"

Plugins

With a Grails plugin the groupId and version are taken from the following properties in the *GrailsPlugin.groovy descriptor:

String groupId = 'myOrg'
String version = '0.1'

The 'artifactId' is taken from the plugin name. For example if you have a plugin called FeedsGrailsPlugin the artifactId will be "feeds". If your plugin does not specify a groupId then this defaults to "org.grails.plugins".

grails.project.dependency.resolution = {
    …
    repositories {
        …
    }
    plugins {
        runtime ':hibernate:1.2.1'
    }
    dependencies {
        …
    }
    …
}

If you don't specify a group id the default plugin group id of org.grails.plugins is used. You can specify to use the latest version of a particular plugin by using "latest.integration" as the version number:

plugins {
    runtime ':hibernate:latest.integration'
}

Integration vs. Release

The "latest.integration" version label will also include resolving snapshot versions. To not include snapshot versions then use the "latest.release" label:

plugins {
    runtime ':hibernate:latest.release'
}

The "latest.release" label only works with Maven compatible repositories. If you have a regular SVN-based Grails repository then you should use "latest.integration".

And of course if you use a Maven repository with an alternative group id you can specify a group id:

plugins {
    runtime 'mycompany:hibernate:latest.integration'
}

Plugin Exclusions

You can control how plugins transitively resolves both plugin and JAR dependencies using exclusions. For example:

plugins {
    runtime(':weceem:0.8') {
        excludes "searchable"
    }
}

Here we have defined a dependency on the "weceem" plugin which transitively depends on the "searchable" plugin. By using the excludes method you can tell Grails not to transitively install the searchable plugin. You can combine this technique to specify an alternative version of a plugin:

plugins {
    runtime(':weceem:0.8') {
        excludes "searchable" // excludes most recent version
    }
    runtime ':searchable:0.5.4' // specifies a fixed searchable version
}

You can also completely disable transitive plugin installs, in which case no transitive dependencies will be resolved:

plugins {
    runtime(':weceem:0.8') {
        transitive = false
    }
    runtime ':searchable:0.5.4' // specifies a fixed searchable version
}