Question

I have a requirement wherein I define a contract in Spring project and want to autowire an external JAR during deploy that implements the contract (set of interfaces). I do not want to enforce the external JAR to be Spring-dependent so that it is as flexible as possible. Is it not possible in my Spring project to use the classes from external JAR as autowire substitutions wherever I am using my contract interfaces? Let me explain with an example:

Spring project:
@Controller
public class MyController {
     @Autowired
     private MyInterface interface;
}

Now the JAR implementing the contract interfaces may be provided by client and I may not know the package names before hand and it could even be a non-Spring project, so it may not be declared with @Component annotation.

e.g.

public class CustomerClass implements MyInterface {
}

Now in my spring project, is there a way to inject CustomerClass in place of MyInterface? I hope my question is clear.

Thanks

Answer 1

@Paddy,
Regarding to your concern about whether you can traditional XML way to achieve the same goal. The following is a sample code showing how to achieve it. Note: the interface MyInterface cannot be dynamic in this way, because the controller is holding a refernece to MyInterface .

Spring application context config :

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
   <property name="locations" value="classpath:test.properties" />
</bean>
<bean id="myInterface" class="${myinterface.impl}"></bean>

MyInterface and two different implementation class

package au.net.test;

public interface MyInterface {

    public String getMessage();
}

public class MyClass1 implements MyInterface{

    public String getMessage(){
        return "message from class 1";
    }
}

public class MyClass2 implements MyInterface{

    public String getMessage() {
        return "message from class 2";
    }   
}

test.properties file under classpath(you can use ant script and maven profile to change property value)

myinterface.impl=au.net.test.MyClass2

web layer Controller (you can inject the implementation class based on dynamic bean candidate)

@Autowired
private MyInterface myInterface;