Examples of com.google.common.eventbus.EventBus

com.google.common.eventbus.EventBus
Dispatches events to listeners, and provides ways for listeners to register themselves.
The EventBus allows publish-subscribe-style communication between components without requiring the components to explicitly register with one another (and thus be aware of each other). It is designed exclusively to replace traditional Java in-process event distribution using explicit registration. It is not a general-purpose publish-subscribe system, nor is it intended for interprocess communication.
Receiving Events
To receive events, an object should:
1. Expose a public method, known as the event handler, which accepts a single argument of the type of event desired;
2. Mark it with a {@link Subscribe} annotation;
3. Pass itself to an EventBus instance's {@link #register(Object)} method.
Posting Events
To post an event, simply provide the event object to the {@link #post(Object)} method. The EventBus instance will determine the typeof event and route it to all registered listeners.
Events are routed based on their type — an event will be delivered to any handler for any type to which the event is assignable. This includes implemented interfaces, all superclasses, and all interfaces implemented by superclasses.
When {@code post} is called, all registered handlers for an event are runin sequence, so handlers should be reasonably quick. If an event may trigger an extended process (such as a database load), spawn a thread or queue it for later. (For a convenient way to do this, use an {@link AsyncEventBus}.)
Handler Methods
Event handler methods must accept only one argument: the event.
Handlers should not, in general, throw. If they do, the EventBus will catch and log the exception. This is rarely the right solution for error handling and should not be relied upon; it is intended solely to help find problems during development.
The EventBus guarantees that it will not call a handler method from multiple threads simultaneously, unless the method explicitly allows it by bearing the {@link AllowConcurrentEvents} annotation. If this annotation isnot present, handler methods need not worry about being reentrant, unless also called from outside the EventBus.
Dead Events
If an event is posted, but no registered handlers can accept it, it is considered "dead." To give the system a second chance to handle dead events, they are wrapped in an instance of {@link DeadEvent} and reposted.
If a handler for a supertype of all events (such as Object) is registered, no event will ever be considered dead, and no DeadEvents will be generated. Accordingly, while DeadEvent extends {@link Object}, a handler registered to receive any Object will never receive a DeadEvent.
This class is safe for concurrent use. @author Cliff Biffle @since Guava release 10


public class GFacNotifier {
    private EventBus eventBus;


    public GFacNotifier(){
        eventBus = new EventBus();
    }

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    private static EventBus bus;


    private static EventBus bus() {
        if (bus == null) {
            bus = new EventBus("erlide");
            bus.register(new ErlideEventBus());
        }
        return bus;
    }

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    private EventBus eventBus;
    private Class<?> listenerInterface;


    @Override
    protected Endpoint createEndpoint(String uri, String remaining, Map<String, Object> parameters) throws Exception {
        EventBus resolvedEventBus = eventBus;
        if (resolvedEventBus == null) {
            resolvedEventBus = CamelContextHelper.mandatoryLookup(getCamelContext(), remaining, EventBus.class);
        }


        return new GuavaEventBusEndpoint(uri, this, resolvedEventBus, listenerInterface);

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    @Test(expected = IllegalStateException.class)
    public void shouldForwardMessageToCamel() throws Exception {
        // Given
        SimpleRegistry registry = new SimpleRegistry();
        registry.put("eventBus", new EventBus());
        CamelContext context = new DefaultCamelContext(registry);
        context.addRoutes(new RouteBuilder() {
            @Override
            public void configure() throws Exception {
                from("guava-eventbus:eventBus?listenerInterface=org.apache.camel.component.guava.eventbus.CustomListener&eventClass=org.apache.camel.component.guava.eventbus.MessageWrapper").

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    private int numberLongEvents = 10;




    @Before
    public void setUp() {
        eventBus = new EventBus();
        deadEventSubscriber = new DeadEventSubscriber();
        eventBus.register(deadEventSubscriber);
        eventPublisher = new EventPublisher(eventBus);
        cashPurchaseEventSubscriber = new CashPurchaseEventSubscriber(eventBus);
        creditPurchaseEventSubscriber = new CreditPurchaseEventSubscriber(eventBus);

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    // Process test classes and resources.
    long start = System.currentTimeMillis();    
    final List<String> testClassNames = processTestResources();


    final EventBus aggregatedBus = new EventBus("aggregated");
    final TestsSummaryEventListener summaryListener = new TestsSummaryEventListener();
    aggregatedBus.register(summaryListener);
    
    for (Object o : listeners) {
      if (o instanceof ProjectComponent) {
        ((ProjectComponent) o).setProject(getProject());
      }
      if (o instanceof AggregatedEventListener) {
        ((AggregatedEventListener) o).setOuter(this);
      }
      aggregatedBus.register(o);
    }


    if (testClassNames.isEmpty()) {
      aggregatedBus.post(new AggregatedQuitEvent());
    } else {
      start = System.currentTimeMillis();
      
      final int slaveCount = determineSlaveCount(testClassNames.size());
      final List<SlaveInfo> slaveInfos = Lists.newArrayList();
      for (int slave = 0; slave < slaveCount; slave++) {
        final SlaveInfo slaveInfo = new SlaveInfo(slave, slaveCount);
        slaveInfos.add(slaveInfo);
      }


      // Order test class names identically for balancers.
      Collections.sort(testClassNames);
      
      // Prepare a pool of suites dynamically dispatched to slaves as they become idle.
      final Deque<String> stealingQueue = 
          new ArrayDeque<String>(loadBalanceSuites(slaveInfos, testClassNames, balancers));
      aggregatedBus.register(new Object() {
        @Subscribe @SuppressWarnings("unused")
        public void onSlaveIdle(SlaveIdle slave) {
          if (stealingQueue.isEmpty()) {
            slave.finished();
          } else {
            String suiteName = stealingQueue.pop();
            slave.newSuite(suiteName);
          }
        }
      });


      // Create callables for the executor.
      final List<Callable<Void>> slaves = Lists.newArrayList();
      for (int slave = 0; slave < slaveCount; slave++) {
        final SlaveInfo slaveInfo = slaveInfos.get(slave);
        slaves.add(new Callable<Void>() {
          @Override
          public Void call() throws Exception {
            executeSlave(slaveInfo, aggregatedBus);
            return null;
          }
        });
      }


      ExecutorService executor = Executors.newCachedThreadPool();
      aggregatedBus.post(new AggregatedStartEvent(slaves.size(), testClassNames.size()));


      try {
        List<Future<Void>> all = executor.invokeAll(slaves);
        executor.shutdown();


        for (int i = 0; i < slaves.size(); i++) {
          Future<Void> f = all.get(i);
          try {
            f.get();
          } catch (ExecutionException e) {
            slaveInfos.get(i).executionError = e.getCause();
          }
        }
      } catch (InterruptedException e) {
        log("Master interrupted? Weird.", Project.MSG_ERR);
      }
      aggregatedBus.post(new AggregatedQuitEvent());


      for (SlaveInfo si : slaveInfos) {
        if (si.start > 0 && si.end > 0) {
          log(String.format(Locale.ENGLISH, "JVM J%d: %8.2f .. %8.2f = %8.2fs",
              si.id,

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    log("Forked JVM process command line (may need escape sequences for your shell):\n" + 
        slave.slaveCommandLine, Project.MSG_VERBOSE);


    commandline.createArgument().setValue(SlaveMain.OPTION_STDIN);


    final EventBus eventBus = new EventBus("slave-" + slave.id);
    final DiagnosticsListener diagnosticsListener = new DiagnosticsListener(slave, this);
    eventBus.register(diagnosticsListener);
    eventBus.register(new AggregatingListener(aggregatedBus, slave));


    final AtomicReference<Charset> clientCharset = new AtomicReference<Charset>();
    final AtomicBoolean clientWithLimitedCharset = new AtomicBoolean(); 
    final PrintWriter w = new PrintWriter(Files.newWriter(classNamesDynamic, Charsets.UTF_8));
    eventBus.register(new Object() {
      @SuppressWarnings("unused")
      @Subscribe
      public void onIdleSlave(final SlaveIdle idleSlave) {
        aggregatedBus.post(new SlaveIdle() {
          @Override

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    // Process test classes and resources.
    long start = System.currentTimeMillis();    
    final TestsCollection testCollection = processTestResources();


    final EventBus aggregatedBus = new EventBus("aggregated");
    final TestsSummaryEventListener summaryListener = new TestsSummaryEventListener();
    aggregatedBus.register(summaryListener);
    
    for (Object o : listeners) {
      if (o instanceof ProjectComponent) {
        ((ProjectComponent) o).setProject(getProject());
      }
      if (o instanceof AggregatedEventListener) {
        ((AggregatedEventListener) o).setOuter(this);
      }
      aggregatedBus.register(o);
    }


    if (testCollection.testClasses.isEmpty()) {
      aggregatedBus.post(new AggregatedQuitEvent());
    } else {
      start = System.currentTimeMillis();


      // Check if we allow duplicate suite names. Some reports (ANT compatible XML
      // reports) will have a problem with duplicate suite names, for example.
      if (uniqueSuiteNames) {
        testCollection.onlyUniqueSuiteNames();
      }


      final int jvmCount = determineForkedJvmCount(testCollection);
      final List<ForkedJvmInfo> slaveInfos = Lists.newArrayList();
      for (int jvmid = 0; jvmid < jvmCount; jvmid++) {
        final ForkedJvmInfo slaveInfo = new ForkedJvmInfo(jvmid, jvmCount);
        slaveInfos.add(slaveInfo);
      }


      
      if (jvmCount > 1 && uniqueSuiteNames && testCollection.hasReplicatedSuites()) {
        throw new BuildException(String.format(Locale.ENGLISH,
            "There are test suites that request JVM replication and the number of forked JVMs %d is larger than 1. Run on a single JVM.",
            jvmCount));
      }


      // Prepare a pool of suites dynamically dispatched to slaves as they become idle.
      final Deque<String> stealingQueue = 
          new ArrayDeque<String>(loadBalanceSuites(slaveInfos, testCollection, balancers));
      aggregatedBus.register(new Object() {
        @Subscribe
        public void onSlaveIdle(SlaveIdle slave) {
          if (stealingQueue.isEmpty()) {
            slave.finished();
          } else {
            String suiteName = stealingQueue.pop();
            slave.newSuite(suiteName);
          }
        }
      });
      
      // Check for filtering expressions.
      @SuppressWarnings("unchecked")
      Vector<Variable> vv = getCommandline().getSystemProperties().getVariablesVector();
      for (Variable v : vv) {
        if (SysGlobals.SYSPROP_TESTFILTER().equals(v.getKey())) {
          try {
            Node root = new FilterExpressionParser().parse(v.getValue());
            log("Parsed test filtering expression: " + root.toExpression(), Project.MSG_INFO);
          } catch (Exception e) {
            log("Could not parse filtering expression: " + v.getValue(), Project.MSG_WARN);
          }
        }
      }


      // Create callables for the executor.
      final List<Callable<Void>> slaves = Lists.newArrayList();
      for (int slave = 0; slave < jvmCount; slave++) {
        final ForkedJvmInfo slaveInfo = slaveInfos.get(slave);
        slaves.add(new Callable<Void>() {
          @Override
          public Void call() throws Exception {
            executeSlave(slaveInfo, aggregatedBus);
            return null;
          }
        });
      }


      ExecutorService executor = Executors.newCachedThreadPool();
      aggregatedBus.post(new AggregatedStartEvent(slaves.size(),
          // TODO: this doesn't account for replicated suites.
          testCollection.testClasses.size()));


      try {
        List<Future<Void>> all = executor.invokeAll(slaves);
        executor.shutdown();


        for (int i = 0; i < slaves.size(); i++) {
          Future<Void> f = all.get(i);
          try {
            f.get();
          } catch (ExecutionException e) {
            slaveInfos.get(i).executionError = e.getCause();
          }
        }
      } catch (InterruptedException e) {
        log("Master interrupted? Weird.", Project.MSG_ERR);
      }
      aggregatedBus.post(new AggregatedQuitEvent());


      for (ForkedJvmInfo si : slaveInfos) {
        if (si.start > 0 && si.end > 0) {
          log(String.format(Locale.ENGLISH, "JVM J%d: %8.2f .. %8.2f = %8.2fs",
              si.id,

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    log("Forked JVM process command line (may need escape sequences for your shell):\n" + 
        slave.slaveCommandLine, Project.MSG_VERBOSE);


    commandline.createArgument().setValue(SlaveMain.OPTION_STDIN);


    final EventBus eventBus = new EventBus("slave-" + slave.id);
    final DiagnosticsListener diagnosticsListener = new DiagnosticsListener(slave, this);
    eventBus.register(diagnosticsListener);
    eventBus.register(new AggregatingListener(aggregatedBus, slave));


    final AtomicReference<Charset> clientCharset = new AtomicReference<Charset>();
    final AtomicBoolean clientWithLimitedCharset = new AtomicBoolean(); 
    final PrintWriter w = new PrintWriter(Files.newWriter(classNamesDynamic, Charsets.UTF_8));
    eventBus.register(new Object() {
      @Subscribe
      public void onIdleSlave(final SlaveIdle idleSlave) {
        aggregatedBus.post(new SlaveIdle() {
          @Override
          public void finished() {

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    * Provides asynchronous {@link EventBus}.
    */
   @Provides
   @Singleton
   EventBus provideSyncEventBus(DeadEventLoggingHandler deadEventsHandler) { // NO_UCD
      EventBus syncBus = new EventBus("jclouds-sync-event-bus");
      syncBus.register(deadEventsHandler);
      return syncBus;
   }

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Examples of com.google.common.eventbus.EventBus

Receiving Events

Posting Events

Handler Methods

Dead Events

Related Classes of com.google.common.eventbus.EventBus