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Java example source code file (CompositeService.java)

This example Java source code file (CompositeService.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

cannot, compositeservice, executionexception, future, injector, interruptedexception, key, list, please, service, set, state, threading, threads, util

The CompositeService.java Java example source code

 * Copyright (C) 2010 Google Inc.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package com.google.inject.service;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Key;

import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

 * A service that composes other services together in a fixed order.
 * @author dhanji@gmail.com (Dhanji R. Prasanna)
public class CompositeService {
  private final Injector injector;

  private final Set<Key services = Sets.newLinkedHashSet();

   * Represents the state of this composite service. Will equal FAILED
   * even if only one component service fails to start or stop. In other
   * words, all component services must start successfully for this
   * service to be considered started and similarly for stopped.
  private volatile Service.State compositeState;
  private boolean composed;

  CompositeService(Injector injector) {
    this.injector = injector;

  public CompositeService add(Class<? extends Service> service) {
    return add(Key.get(service));

  public CompositeService add(Key<? extends Service> service) {
        "Cannot reuse a CompositeService after it has been compose()d. Please create a new one.");
    // Verify that the binding exists. Throws an exception if not.

    return this;

  public Service compose() {
        "Cannot reuse a CompositeService after it has been compose()d. Please create a new one.");
    composed = true;

    // Defensive copy.
    final List<Key services = ImmutableList.copyOf(this.services);

    return new Service() {
      public Future<State> start() {
        final List<Future tasks = Lists.newArrayList();
        for (Key<? extends Service> service : services) {

        return futureGet(tasks, State.STARTED);

      public Future<State> stop() {
        final List<Future tasks = Lists.newArrayList();
        for (Key<? extends Service> service : services) {

        return futureGet(tasks, State.STOPPED);

      public State state() {
        return compositeState;

  private FutureTask<Service.State> futureGet(final List> tasks,
      final Service.State state) {
    return new FutureTask<Service.State>(new Callable() {
      public Service.State call() {
        boolean ok = true;
        for (Future<Service.State> task : tasks) {
          try {
            ok = state == task.get();
          } catch (InterruptedException e) {
            return compositeState = Service.State.FAILED;
          } catch (ExecutionException e) {
            return compositeState = Service.State.FAILED;

        return compositeState = ok ? state : Service.State.FAILED;

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