Luc Dewavrin's weblog

A Groovy Use Case

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I recently discovered Spring’s ability to declare beans that are script-based. This feature can be used to mock business interfaces with Groovy implementations. In a JavaEE container where startup and redeployment can take a while, it can be very useful, in pre-integration tests, to change the behaviour of your business services especially without redeploying the whole EAR or restarting the server.Here’s an example declaration:

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<bean id="MockServiceImpl" class="org.springframework.scripting.groovy.GroovyScriptFactory">
  <constructor-arg value="${mocks.path}/MockServiceImpl.groovy"></constructor-arg>
</bean>

<bean class="org.springframework.scripting.support.ScriptFactoryPostProcessor">
  <property name="defaultRefreshCheckDelay" value="2"></property>
</bean>

The “defaultRefreshCheckDelay” parameter sets the delay in seconds between checks for modifications of the script. and the groovy script: Liquid error: ClassNotFound: no lexer for alias ‘groovy’ found

I see many benefits in this solution:

  • hot-swapping implementations without redeployment.
  • returned objects can be dynamically generated. For instance if you want to return objects depending only one a given parameter it can be done easily.
  • more concise than XML (see xmlstubs a XML based mocking solution).

On a side note, groovy requires ASM 2.2.2 library so if you use hibernate use the cglib with no dependency library which includes asm classes in renamed packages. Also use Spring 2.0.3+ if you use AspectJ pointcut declarations or you can expect errors.With maven profiles it ‘s easy to build a mock and non-mocked service layer of an EAR.Note that you can still inject the real implementations if you want to delegate work to it.

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<bean id="MockServiceImpl" class="org.springframework.scripting.groovy.GroovyScriptFactory">
  <constructor-arg value="${mocks.path}/MockServiceImpl.groovy"/>
  <constructor-arg value="ServiceImpl"/>
</bean>

On an other side note, I like both Groovy and JRuby but now tend to prefer Groovy because it leverages my knowledge of Java API. With Ruby i spend too much time finding the reference web site how to achieve things that i do almost naturally in Java. OTH, Ruby has its core API use closures. Closures are tightly integrated and tend to favor loose coupling.

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