class MyController {
    def hello() {
        def recipient = grailsApplication.config.getProperty('foo.bar.hello')

        render "Hello ${recipient}"
    }
}

class MyController {

    def hello(Recipient recipient) {
        //Retrieve Integer property 'foo.bar.max.hellos', otherwise use value of 5
        def max = grailsApplication.config.getProperty('foo.bar.max.hellos', Integer, 5)

        //Retrieve property 'foo.bar.greeting' without specifying type (default is String), otherwise use value "Hello"
        def greeting = grailsApplication.config.getProperty('foo.bar.greeting', "Hello")

        def message = (recipient.receivedHelloCount >= max) ?
          "Sorry, you've been greeted the max number of times" :  "${greeting}, ${recipient}"
        }

        render message
    }
}

import grails.core.*

class MyService {
    GrailsApplication grailsApplication

    String greeting() {
        def recipient = grailsApplication.config.getProperty('foo.bar.hello')
        return "Hello ${recipient}"
    }
}

import grails.core.support.GrailsConfigurationAware

class MyService implements GrailsConfigurationAware {

    String recipient

    String greeting() {
        return "Hello ${recipient}"
    }

    void setConfiguration(Config config) {
        recipient = config.getProperty('foo.bar.hello')
    }

}

import org.springframework.beans.factory.annotation.*

class MyController {
    @Value('${foo.bar.hello}')
    String recipient

    def hello() {
        render "Hello ${recipient}"
    }
}

production:
    dataSource:
        url: '${JDBC_CONNECTION_STRING}'

bootRun {
    systemProperties = System.properties
}

test {
    systemProperties = System.properties
}

class Application extends GrailsAutoConfiguration {
    @Override
    Collection<String> packageNames() {
        super.packageNames() + ['my.additional.package']
    }

    ...
}

class Application extends GrailsAutoConfiguration {
    @Bean
    MyType myBean() {
        return new MyType()
    }

    ...
}

environments:
    development:
        dataSource:
            dbCreate: create-drop
            url: jdbc:h2:mem:devDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
    test:
        dataSource:
            dbCreate: update
            url: jdbc:h2:mem:testDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
    production:
        dataSource:
            dbCreate: update
            url: jdbc:h2:prodDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
            properties:
               jmxEnabled: true
               initialSize: 5
        ...

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"
            properties {
               jmxEnabled = true
               initialSize = 5
            }
        }
    }
}

grails <<environment>> <<command name>>

grails test war

./gradlew bootRun -Dgrails.env=UAT

import grails.util.Environment

...

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

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

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

dataSource:
    pooled: true
    jmxExport: true
    driverClassName: org.h2.Driver
    username: sa
    password:

environments:
    development:
        dataSource:
            dbCreate: create-drop
            url: jdbc:h2:mem:devDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
    test:
        dataSource:
            dbCreate: update
            url: jdbc:h2:mem:testDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
    production:
        dataSource:
            dbCreate: update
            url: jdbc:h2:prodDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
            properties:
               jmxEnabled: true
               initialSize: 5

dataSource:
    pooled: true
    jmxExport: true
    driverClassName: org.h2.Driver
    username: sa
    password:

dataSources:
    lookup:
        dialect: org.hibernate.dialect.MySQLInnoDBDialect
        driverClassName: com.mysql.jdbc.Driver
        username: lookup
        password: secret
        url: jdbc:mysql://localhost/lookup
        dbCreate: update

environments:
    development:
        dataSource:
            dbCreate: create-drop
            url: jdbc:h2:mem:devDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
    test:
        dataSource:
            dbCreate: update
            url: jdbc:h2:mem:testDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
    production:
        dataSource:
            dbCreate: update
            url: jdbc:h2:prodDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE
            properties:
                jmxEnabled: true
                initialSize: 5
                ...
        dataSources:
            lookup:
                dialect: org.hibernate.dialect.Oracle10gDialect
                driverClassName: oracle.jdbc.driver.OracleDriver
                username: lookup
                password: secret
                url: jdbc:oracle:thin:@localhost:1521:lookup
                dbCreate: update

DataSource dataSource_lookup

class ZipCode {

   String code

   static mapping = {
      datasource 'lookup'
   }
}

class ZipCode {

   String code

   static mapping = {
      datasources(['lookup', 'auditing'])
   }
}

class ZipCode {

   String code

   static mapping = {
      datasources(['lookup', 'DEFAULT'])
   }
}

class ZipCode {

   String code

   static mapping = {
      datasource 'ALL'
   }
}

class ZipCode {

   String code

   static mapping = {
      datasources(['lookup', 'auditing'])
   }
}

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

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          '-//Hibernate/Hibernate Configuration DTD 3.0//EN'
          'http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd'>
<hibernate-configuration>
   <session-factory>
      <mapping class='org.example.Book'/>
   </session-factory>
</hibernate-configuration>

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          '-//Hibernate/Hibernate Configuration DTD 3.0//EN'
          'http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd'>
<hibernate-configuration>
   <session-factory>
      <mapping class='org.example.Library'/>
   </session-factory>
</hibernate-configuration>

class DataService {

   static datasource = 'lookup'

   void someMethod(...) {
      ...
   }
}

grails:
  transaction:
    chainedTransactionManagerPostProcessor:
      enabled: true

grails:
  transaction:
    chainedTransactionManagerPostProcessor:
      enabled: true
      blacklistPattern: '.*'

def version = grailsApplication.metadata.getApplicationVersion()

def grailsVersion = grailsApplication.metadata.getGrailsVersion()

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