Proxy object throws NullPointerException

Question

I'm using Java 1.8.

Here is my interface which extends ExecutorService:

public interface ConsumerExecutor extends ExecutorService{

    boolean closed();

}

Here is my InvocationHandler class:

public class ExecutorInvocationHandler implements InvocationHandler {

    private boolean close = false;
    private ExecutorService executor;

    public ExecutorInvocationHandler(ExecutorService exec) {
        this.executor = exec;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        if (method.getName().equals("closed")) {
            return closed();
        } else if (method.getName().equals("shutdown")) {
            _close();
            executor.shutdown();
        } else if (method.getName().equals("shutdownNow")) {
            _close();
            executor.shutdownNow();
        } else {
            method.invoke(executor, args);
        }

        return null;
    }

    public synchronized void _close() {
        close = true;
    }

    public synchronized boolean closed() {
        return close;
    }
}

Now, the following code, running from a JUnit test:

        ConsumerExecutor exec = ConsumerFactory.newInstance(ExecutorInvocationHandler.class,
                Executors.newCachedThreadPool());
        //do something here
        while (!exec.isTerminated()) {//line 52
        }
        //do soemthing

throws this exception:

java.lang.NullPointerException
    at com.sun.proxy.$Proxy3.isTerminated(Unknown Source)
    at test.de.edigrid.util.upgrade_test.tasks.ContextsCollectorTest.collectorTest(ContextsCollectorTest.java:52)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
    at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
    at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)

The proxy factory method is here:

    public static ConsumerExecutor newInstance(Class clazz, ExecutorService exec) {
        if (clazz == ExecutorInvocationHandler.class) {
            return (ConsumerExecutor) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
                    new Class[] { ConsumerExecutor.class }, new ExecutorInvocationHandler(exec));
        }
        return null;
    }

Can anybody give me a hint why this exception?

Answer 1

The problem was related to function return. I forgot to put method.invoke(...) after return statement. It should have been something like this:

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        if (method.getName().equals("closed")) {
            return closed();
        } else if (method.getName().equals("shutdown")) {
            _close();
            executor.shutdown();
        } else if (method.getName().equals("shutdownNow")) {
            _close();
            return executor.shutdownNow();
        } else {
            return method.invoke(executor, args);
        }

        return null;
    }