Qualifying Spring dependency injection for field from superclass

Question

How I can inject my webServiceTemplate in the implementing class?

My example:

public abstract class AbstractConnector {

    protected WebServiceTemplate webServiceTemplate;

    protected Object send(Object message) {
        return webServiceTemplate.marshalSendAndReceive();

   }

}

And in my concrete implementation I would like to set my webServiceTemplate like this.

public class MyConnector extends AbstractConnector {

   @Resource(name = "myWebService")
   private WebServiceTemplate webServiceTemplate;
}

But this is not OK. If I call the send() , then I will get NPE because webServiceTemplate is null. How to set this dependency in implementation which will be accessible in the send() method?

Answer 1

It's best to avoid field injection whenever possible, and this is an example why. Constructor injection makes this simple:

public abstract class AbstractConnector {
    private final WebServiceTemplate webServiceTemplate;

    protected AbstractConnector(WebServiceTemplate webServiceTemplate) {
        this.webServiceTemplate = webServiceTemplate;
    }
}

@Service
public class MyConnector extends AbstractConnector {

    @Inject // or @Autowired
    public MyConnector(@Qualifier("myWebService") WebServiceTemplate webServiceTemplate) {
        super(webServiceTemplate);
    }
}

Answer 2

I do not see why field injection would be any less simple here:

public abstract class AbstractConnector {
    protected WebServiceTemplate webServiceTemplate;

    public void setWebServiceTemplate(WebServiceTemplate template) {
        this.webServiceTemplate = template;
    }
}

public class MyConnector extends AbstractConnector {

    @Autowired("myWebService")
    @Override
    public void setWebServiceTemplate(WebServiceTemplate template) {
        super.setWebServiceTemplate(template);
    }
}

Answer 3

You can use method-lookup :

You abstract class:

public abstract class AbstractConnector 
{

private abstract WebServiceTemplate getWebServiceTemplate();

protected Object send(Object message) 
{
    return getWebServiceTemplate().marshalSendAndReceive();
}

Your configuration:

   <bean id="webServiceTemplate" scope="prototype" class="com.example.WebServiceTemplate" />
   <bean id="connector" class="com.example.AbstractConnector"
        <lookup-method name="webServiceTemplate" bean="webServiceTemplate" />
    </bean>

Spring will wire you abstract class to return a fresh webServiceTemplate if the method getWebServiceTemplate() is called.