Sounds complicated, not a Problem with Spring!

First we have to annotate the Command with @Configurable:

@Configurable(autowire = Autowire.BY_TYPE, preConstruction = true)

public class CreateUserCmd {

private UserDAO dao;

public CreateUserCmd (String username) {

if(dao.findByUsername(username)) {

throw new IllegalArgumentException("User already exists!");

}

}

// getter/setter for dao

}

So what are we doing here. We are telling Spring that this Command Type (autowire) should be configured before the constructor (preConstruction). Configured with what? It wouldn’t be Spring without XML. Therefore, we are defining a prototype bean for our Command, so Spring knows what should be injected.

Spring knows where to inject, but not what. For our tests we said that we are creating a mock class. I will omit the class here, but we have to define a Spring bean for it:

...

Note, that the mock “id” and the “ref” are the same and we are enabling AOP. Now Spring knows everything it needs. Not really, because we have to configure how the injection is done. In our case we are using AspectJ for AOP which weaves the necessary code into our class. All needed jar files are coming with Spring. We need to include “spring-aspects.jar” and “aspectjweaver.jar”. The Spring configuration is complete, but AspectJ needs some more information. We are creating the XML aop.xml in the folder META-INF:

Viola, we are done! Now we only have to tell the compiler to use the weaver with “-javaagent:lib/aspectjweaver.jar”. Download the Sample Project (includes all libaries and code excamples).

More information can be found here and here.

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