Inheritance (Late Binding) via Dependency Injection in Java

Question

I am using Spring DI to wire my components and I came across this issue.

I have a BaseService class which has multiple implementations. And the layer above it, has a builder which calls the service to get data to populate POJOs. Service implementation I need to call (ServiceA,ServiceB) changes according to the type of POJO I need to build.

In such case, how can I autowire the service, as it requires late binding the service. How can I tackle this kind of scenario? (Example in Spring DI would really help)

I read similar questions but could not find the answer. And I read that SOA patterns such as Service Host provide different solutions to exact use case.

Please help. Thanks

Answer 1

You can use ServiceLocatorFactoryBean. In your case you would do something like this:

public interface BaseServiceLocator {

   BaseService lookup(String qualifier); //use whatever qualifier type makes sense here
}

<bean id="serviceLocatorFactoryBean"
    class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean">
    <property name="serviceLocatorInterface"
              value="your.package.BaseServiceLocator" />
</bean>

Then your builder would look something like this:

public class Builder {

  @Autowired
  private BaseServiceLocator baseServiceLocator;

  @Override
  public YourReturnType businessMethod() {
      SomeData data = getData();
      BaseService baseService = baseServiceLocator(data.getType()); //here I am assuming that getType() is a String

      //whatever
  }