Java @Inject无法正常工作-方法返回null

Question

Not sure as to why the interface doesn't get injected. The test always returns null. I've got the beans.xml as well in WEB-INF . Why does it return null?

I've also tried to annotate the service class with @ApplicationScoped and a class that produces a new TImpl

public interface T {
 int test_method(int n );
 public void addToSession(Session session);
} 

@Handler // Qualifier
public TImpl implements T{

 private static Set<Session> sessions = Collections.synchronizedSet(new HashSet<Session>());
 public TImpl();

 @Override
 int test_method(int n){ return n * 2; }

 @Override
 public void addToSession(Session session){ 
  sessions.add(session);
}
}

public class TService implements Serializable {

 private @Inject @Handler T;

 public TService() {}
 ... 

 int test_method_service(int n) { return T.test_method(n); }
 public void addToSession(Session session) { T.addToSession(session); }

}

public class L extends Endpoint {

 TService service;

 public L(TService s){ this.service = t; }
 public L(){}


 @Override
 public void OnOpen(Session session, ... ) 

 servive.addToSession(session); // null pointer
 ...
}

Stacktrace

java.lang.NullPointerException
at com.vio.sockets.configuration.MessageEndPoint.onOpen(MessageEndPoint.java:40)
at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:133)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:914)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1457)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)

Answer 1

You say that your test returns null , but the stacktrace tells a different story: expected:<6> but was:<0> is not a NullPointerException , it means that the call to service.test_method_service(3) return 0 – that's zero.

This seems just like the expected behaviour of a Mockito mock: You have a mock for T injected into your service instance, it calls test_method() in the mock for T, and Mockito's default value for methods returning int is 0.

When you want a different behaviour, you have to set the mock's behaviour:

Mockito.when(t.test_method(3)).thenReturn(6);