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Java example source code file (Service.java)

This example Java source code file (Service.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

failed, future, service, started, state, stopped, threading, threads

The Service.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,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.service;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

/**
 * An object with an operational state, asynchronous {@link #start()} and
 * {@link #stop()} lifecycle methods to transition in and out of this state.
 * Example services include http servers, RPC systems and timer tasks.
 *
 * @author dhanji@gmail.com (Dhanji R. Prasanna)
 */
public interface Service {
  /**
   * If the service has already been started, this method returns
   * immediately without taking action. A stopped service may not be restarted.
   *
   * @return a future for the startup result, regardless of whether this call
   *     initiated startup. Calling {@link Future#get} will block until the
   *     service has finished starting, and returns the resultant state. If
   *     the service fails to start, {@link Future#get} will throw an {@link
   *     ExecutionException}. If it has already finished starting,
   *     {@link Future#get} returns immediately.
   */
  Future<State> start();

  /**
   * If the service is {@link State#STARTED} initiates service shutdown and
   * returns immediately. If the service has already been stopped, this
   * method returns immediately without taking action.
   *
   * @return a future for the shutdown result, regardless of whether this call
   *     initiated shutdown. Calling {@link Future#get} will block until the
   *     service has finished shutting down, and either returns {@link
   *     State#STOPPED} or throws an {@link ExecutionException}. If it has
   *     already finished stopping, {@link Future#get} returns immediately.
   */
  Future<State> stop();

  /**
   * Returns the current state of this service. One of {@link State} possible
   * values, or null if this is a brand new object, i.e., has not been put into
   * any state yet.
   */
  State state();

  /**
   * The lifecycle states of a service.
   */
  enum State { STARTED, STOPPED, FAILED }
}

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