(Quick Reference)

3. Configuration - Reference Documentation

Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith

Version: 1.4.0.M1

3. Configuration

It may seem odd that in a framework that embraces "convention-over-configuration" that we tackle this topic now, but since what configuration there is typically a one off, it is best to get it out the way.

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

However, typically you want to set-up a real database at some point and the way you do that is described in the following section.

3.1 Basic Configuration

For general configuration Grails provides a file called grails-app/conf/Config.groovy. This file uses Groovy's ConfigSlurper which is very similar to Java properties files except it is pure Groovy hence you can re-use variables and use proper Java types!

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 via 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

3.1.1 Built in options

Grails also provides the following configuration options:
  • 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 location where the war command should place the generated WAR file
  • grails.war.dependencies - A closure containing Ant builder syntax or a list of JAR filenames. Allows you to customise what libaries are included in the WAR file.
  • grails.war.java5.dependencies - A list of the JARs that should be included in the WAR file for JDK 1.5 and above.
  • grails.war.copyToWebApp - A closure containing Ant builder syntax that is legal inside an Ant copy, for example "fileset()". Allows you to 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 pre-warring stuff it needs to.

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

3.1.2 Logging

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.mortbay.log' }

This says that for the two 'org.codehaus.groovy.*' loggers, only messages logged at 'error' level and above will be shown. The 'org.mortbay.log' logger also shows messages at the 'warn' level. 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 uniquely identified by name and if two separate classes use loggers with the same name, those loggers are effectively 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, say 'controller' or 'service, and className is the fully qualified name of the artifact. For example, let's say you have this service:

package org.example

class MyService { … }

then the name of the logger will be 'grails.app.service.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. 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 a logger in Grails:

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

This example configures a logger named 'org.codehaus.groovy.grails.web.servlet' to ignore any messages sent to it 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 effectively hierarchical. This makes configuring them by package much, 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. To do that you'll need to use the convention mentioned earlier: 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 debug "grails.app.controller.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:

  • bootstrap - For bootstrap classes
  • dataSource - For data sources
  • tagLib - For tag libraries
  • service - For service classes
  • controller - 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 allows you to 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:

NameClassDescription
jdbcJDBCAppenderLogs to a JDBC connection.
consoleConsoleAppenderLogs to the console.
fileFileAppenderLogs to a single file.
rollingFileRollingFileAppenderLogs to rolling files, for example a new file each day.

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 via the above syntax, then you can 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.controller.BookController"

This will ensure that the 'org.codehaus.groovy.grails.commons' logger and its children send log messages to 'myAppender' as well as any appenders configured for the root logger. If you want to add more than one appender to the logger, then add them to the same level declaration:

error myAppender:      "grails.app.controller.BookController",
      myFileAppender:  ["grails.app.controller.BookController", "grails.app.service.BookService"],
      rollingFile:     "grails.app.controller.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.controller.BookController"
debug myFileAppender:  "grails.app.controller.BookController"
fatal rollingFile:     "grails.app.controller.BookController"

you'd find that only 'fatal' level messages get logged for 'grails.app.controller.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.

Let's say an appender is attached to a logger configured with the 'all' level. That will give us a lot of logging information that may be fine in a file, but 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 of course 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 round 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.controller"

environments { production { // Override previous setting for 'grails.app.controller' error "grails.app.controller" } } }

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? In that case, you need to change the 'additivity' for a logger.

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.controller.BookController", "grails.app.service.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.controller.BookController", "grails.app.service.BookService"

3.1.3 GORM

Grails provides the following GORM configuration options:
  • 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.

Enable failOnError for all domain classes…

grails.gorm.failOnError=true

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 do something like save(flush: true).

3.2 Environments

Per Environment Configuration

Grails supports the concept of per environment configuration. Both the Config.groovy file and the DataSource.groovy file within the grails-app/conf directory can take advantage of 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.hsqldb.jdbcDriver"
    username = "sa"
    password = ""
}
environments {
    development {
        dataSource {
            dbCreate = "create-drop" // one of 'create', 'create-drop','update'
            url = "jdbc:hsqldb:mem:devDB"
        }
    }
    test {
        dataSource {
            dbCreate = "update"
            url = "jdbc:hsqldb:mem:testDb"
        }
    }
    production {
        dataSource {
            dbCreate = "update"
            url = "jdbc:hsqldb:file:prodDb;shutdown=true"
        }
    }
}

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. This syntax can also be used within Config.groovy.

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 could do:

grails test war

If you have other environments that you need to target 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
    }
}

3.3 The DataSource

Since Grails is built on Java technology setting up a data source requires some knowledge of JDBC (the technology that doesn't stand for Java Database Connectivity).

Essentially, if you are using another database other than HSQLDB you need to have a JDBC driver. For example for MySQL you would need Connector/J

Drivers typically come in the form of a JAR archive. Drop the JAR into your project's lib directory.

Once you have the JAR in place 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 or not - 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
  • 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.
  • 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 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 - Creates the schema on startup, clearing any existing tables and data first.
  • create-drop - Same as create, but also drops the tables when the application shuts down.
  • update - Updates the current schema without dropping any tables or data. Note that this can't properly handle certain schema changes like column renames (you're left with the old column containing the existing data).
  • validate - Checks that the current schema matches the domain model, but doesn't modify the database in any way.

You can also remove the dbCreate setting completely, which is recommended once you have an application and database in production. Database changes then have to be managed through proper migrations, either via SQL scripts or a migration tool like Liquibase (for which there is a plugin).

3.3.1 DataSources and Environments

The previous example configuration assumes you want the same config for all environments: production, test, development etc.

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

dataSource {
    // common settings here
}
environments {
    production {
        dataSource {
            url = "jdbc:mysql://liveip.com/liveDb"
        }
    }
}

3.3.2 JNDI DataSources

Referring to a JNDI DataSource

Since many Java EE containers typically supply DataSource instances via the Java Naming and Directory Interface (JNDI). Sometimes you are required to look-up a DataSource via 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 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.hsql.jdbcDriver",
        url: "jdbc:HypersonicSQL:database",
        username: "dbusername",
        password: "dbpassword",
        maxActive: "8",
        maxIdle: "4"
    ],
    "mail/session": [
        type: "javax.mail.Session,
        auth: "Container",
        "mail.smtp.host": "localhost"
    ]
]

3.3.3 Automatic Database Migration

The dbCreate property of the DataSource definition is important as it dictates what Grails should do at runtime with regards to automatically generating the database tables from GORM classes. The options are:
  • create-drop - Drops and re-creates the database when Grails starts, and drops the schema at the end of a clean shutdown.
  • create - Drops and re-creates the database when Grails starts, but doesn't drop the schema at the end of a clean shutdown.
  • update - Creates the database if it doesn't exist, and modifies it if it does exist. The modifications are rather basic though, and generally only include adding missing columns and tables. Will not drop or modify anything.
  • validate - Makes no changes to your database. Compares the configuration with the existing database schema and reports warnings.
  • any other value - does nothing. Don't specify any value if you want to manage databases yourself or by using a 3rd-party tool.

Both create-drop and create will destroy all existing data hence use with caution!

In development mode dbCreate is by default set to "create-drop":

dataSource {
   dbCreate = "create-drop" // one of 'create', 'create-drop','update'
}

What this does is automatically drop and re-create the database tables on each restart of the application. Obviously this may not be what you want in production.

Although Grails does not currently support Rails-style Migrations out of the box, there are currently three plugins that provide similar capabilities to Grails: Autobase (http://wiki.github.com/RobertFischer/autobase), The LiquiBase plugin and the DbMigrate plugin both of which are available via the grails list-plugins command

3.3.4 Transaction-aware DataSource Proxy

The actual dataSource bean is wrapped in a transaction-aware proxy so you will be given the connection that's being used by the current transaction or Hibernate Session if one is active.

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

3.3.5 Database Console

The H2 database console is a convenient feature of H2 that provides a web-based interface to any database that you have a JDBC driver for, and it's very useful to view the database you're developing against. It's especially useful when running against an in-memory database.

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.

3.4 Externalized Configuration

Some deployments require that configuration be sourced from more than one place and be changeable without requiring a rebuild of the application. In order to support deployment scenarios such as these the configuration can be externalized. To do so you need to point Grails at the locations of the configuration files Grails should be using by adding a grails.config.locations setting in Config.groovy:

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

3.5 Versioning

Versioning Basics

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

To change the version of your application you can 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']

If it is the version of Grails you need you can use:

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

or the GrailsUtil class:

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

3.6 Project Documentation

Since Grails 1.2, the documentation engine that powers the creation of this documentation is available to your Grails projects.

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. Firstly you need to create a src/docs/guide directory and then have numbered text files using the gdoc format. For example:

+ src/docs/guide/1. Introduction.gdoc
+ src/docs/guide/2. Getting Started.gdoc

The title of each chapter is taken from the file name. The order is dictated by the numerical value at the beginning of the file name.

Creating reference items

Reference items appear in the left menu on the documentation and are useful for quick reference documentation. Each reference item belongs to a category and a category is a directory located in the src/docs/ref directory. For example say you defined a new method called renderPDF, that belongs to a category called Controllers this can be done by creating 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.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 name of the documentation and the version are pulled from your project itself.

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 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:

[Intro|guide:1. Introduction]

The documentation engine will warn you if any links to sections in your guide break. Sometimes though it is preferable not to hard code the actual names of guide sections since you may move them around. To get around this you can create an alias inside grails-app/conf/Config.groovy:

grails.doc.alias.intro="1. Introduction"

And then the link becomes:

[Intro|guide:intro]

This is useful since if you linked the to "1. Introduction" chapter many times you would have to change all of those links.

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. If you want 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/api"

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:

NameNumber
Albert46
Wilma1348
James12

{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}

3.7 Dependency Resolution

In order to control how JAR dependencies are resolved Grails features (since version 1.2) a dependency resolution DSL that allows you to control how dependencies for applications and plugins are resolved.

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

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

The default configuration looks like the following:

grails.project.dependency.resolution = {
    // inherit Grails' default dependencies
    inherits("global") {
        // uncomment to disable ehcache
        // excludes 'ehcache'
    }
    log "warn" // log level of Ivy resolver, either 'error', …
    repositories {
        grailsPlugins()
        grailsHome()
        grailsCentral()

// uncomment the below to enable remote dependency resolution // from public Maven repositories //mavenLocal() //mavenCentral() //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 'mysql:mysql-connector-java:5.1.5' } }

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

3.7.1 Configurations and Dependencies

Grails features 5 dependency resolution configurations (or 'scopes') which you can take advantage of:
  • 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 as such:

runtime 'com.mysql:mysql-connector-java:5.1.5'

The above uses the string syntax which is group:name:version. You can also use a map-based syntax:

runtime group:'com.mysql',
        name:'mysql-connector-java',
        version:'5.1.5'

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:5.1.5',
        'net.sf.ehcache:ehcache:1.6.1'

// Or

runtime( [group:'com.mysql', name:'mysql-connector-java', version:'5.1.5'], [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:5.1.5',
        'net.sf.ehcache:ehcache:1.6.1') {
    transitive = false
}

// Or runtime group:'com.mysql', name:'mysql-connector-java', version:'5.1.5', 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:5.1.5',
        'net.sf.ehcache:ehcache:1.6.1') {
    excludes "xml-apis", "commons-logging"
}

// Or runtime(group:'com.mysql', name:'mysql-connector-java', version:'5.1.5') { 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:5.1.5',
        'net.sf.ehcache:ehcache:1.6.1') {
    exclude "xml-apis"
}

Using Ivy module configurations

If you are using 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).

3.7.2 Dependency Repositories

Remote Repositories

Grails, when installed, does not use any remote public repositories. There is a default grailsHome() repository that will locate the JAR files Grails needs from your Grails installation. If you want to take advantage of a public repository you need to specify as such inside 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"
}

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.

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

A common question is whether it's possible to pull dependencies from a repository using SSH. The answer is yes! 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 }

If you're going to use the SSH resolver, then you will need to download the JSch JAR and add it to Grails' classpath. You can either do this by adding its path to the CLASSPATH environment variable or by passing the path in the Grails command line:

grails -classpath /path/to/jsch compile|run-app|etc.
The environment variable is more convenient, but be aware that 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 some form of authentication you can specify as such using a credentials block:

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

The above can also 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"
    }
}

3.7.3 Debugging Resolution

If you are having trouble getting a dependency to resolve you can enable more verbose debugging from the underlying engine using the log method:

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

3.7.4 Inherited Dependencies

By default every Grails application inherits a bunch of framework dependencies. This is done through the line:

inherits "global"

Inside the BuildConfig.groovy file. If you wish exclude certain inherited dependencies then you can do so using the excludes method:

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

3.7.5 Providing Default Dependencies

Most Grails applications will have runtime dependencies on a lot of jar files that are provided by the Grails framework. These include libraries like Spring, Sitemesh, Hibernate etc. When a war file is created, all of these dependencies will be included in it. But, an application may choose to exclude these jar files from the war. This is useful when the jar files will be provided by the container, as would normally be the case if multiple Grails applications are deployed to the same container. 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 { // … } }

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

3.7.6 Dependency Reports

As mentioned in the previous section a Grails application consists of dependencies inherited from the framework, the plugins installed and the application dependencies itself.

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

grails dependency-report

This will output a report to the target/dependency-report directory by default. You can specify which configuration (scope) you want a report for by passing an argument containing the configuration name:

grails dependency-report runtime

3.7.7 Plugin JAR Dependencies

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.

If you want 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:

compile( 'org.hibernate:hibernate-core:3.3.1.GA') {
    export = false
}

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

compile group: 'org.hibernate', name: 'hibernate-core',
        version: '3.3.1.GA', 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 {
    runtime( "org.grails.plugins:hibernate:1.3.0" ) {
        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.

3.7.8 Maven Integration

When using the Grails Maven plugin, Grails' dependency resolution mechanics are disabled as it is assumed that you will manage dependencies via Maven's pom.xml file.

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.

3.7.9 Deploying to a Maven Repository

If you are using Maven to build your Grails project, you can use the standard Maven targets mvn install and mvn deploy. If not, you can deploy a Grails project or plugin to a Maven repository using the maven-publisher plugin.

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. You need to configure the details of the repository specified by this 'id' within your grails-app/conf/BuildConfig.groovy file or in your USER_HOMER/.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 if you need to explicitly 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".

3.7.10 Plugin Dependencies

As of Grails 1.3 you can declaratively specify plugins as dependencies via the dependency DSL instead of using the install-plugin command:

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. If you don't want to include snapshot versions then you can 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 are using 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
}