As you may know, Grails is actually a Spring MVC application in disguise. Meanwhile dependency injection is the key point of Spring. Thus a quite natural problem for newcomers to Grails is that: how to configure more beans? Actually it’s as easy as in Spring.
Static Configuration:
- Using XML:
Beans can be configured using the “grails-ap/conf/spring/resources.xml” file of your applications using the same syntax as Spring. E.g.
<bean id=”myBean” class=”my.company.MyBeanImpl”></bean>
- Using the Spring DSL:
Define in “grails-app/conf/spring/resources.groovy”(create it if it doesn’t exist) as below:
Beans = {
switch(Environment.current) {
case Environment.PRODUCTION:
myBean(my.company.MyBeanImpl) {
bookService = ref(“bookService”)
}
break
case Environment.DEVELOPMENT:
myBean(my.company.mock.MockImpl) {
bookService = ref(“bookService”)
}
break
}
As you may notice, the biggest advantage of this way is you can mix logic in within your bean definitions (have different configuration under different environment in this example)
Runtime Configuration:
Normal cases: use a “grails.spring.BeanBuilder” class that use dynamic Groovy to construct beans. E.g.
Def bb = new grails.spring.BeanBuilder()
bb.beans {
dataSource(BasicDataSource) {
driverClassName = “org.hsqldb.jdbcDriver”
url = “jdbc:hsqldb:mem:graislDB”
…
}
}
Within plug-ins, you don’t need to instantiate a BeanBuilder. Instead the DSL is defined inside the “doWithSpring”.
Some explanation about BeanBuilder DSL:
Novices may get confused about this syntax (me too when I get first contact with Grails!) Actually it’s often used in Grails and not so much complex.
Suppose we have a bean class as follow:
MyExampleBean(String foo,int bar)
We can instantiate a bean as:
exampleBean(MyExampleBean, “stringArgument”,2) { … }
where “exampleBean” is the bean variable name and “MyExampleBean” is the bean class name. “stringArgument” is assigned to foo, 2 is assigned to bar.
It’s quite simple, right? Of course, you can visit “Grails and Spring” chapter of Grails doc for more details.
Useful links:
“Grails and Spring” chapter: http://grails.org/doc/latest/guide/spring.html
Groovy doc: http://groovy.codehaus.org/User+Guide
