1 /** 2 * Copyright (C) 2010 Google Inc. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.inject.service; 18 19 import java.util.concurrent.ExecutionException; 20 import java.util.concurrent.Future; 21 22 /** 23 * An object with an operational state, asynchronous {@link #start()} and 24 * {@link #stop()} lifecycle methods to transition in and out of this state. 25 * Example services include http servers, RPC systems and timer tasks. 26 * 27 * @author dhanji (at) gmail.com (Dhanji R. Prasanna) 28 */ 29 public interface Service { 30 /** 31 * If the service has already been started, this method returns 32 * immediately without taking action. A stopped service may not be restarted. 33 * 34 * @return a future for the startup result, regardless of whether this call 35 * initiated startup. Calling {@link Future#get} will block until the 36 * service has finished starting, and returns the resultant state. If 37 * the service fails to start, {@link Future#get} will throw an {@link 38 * ExecutionException}. If it has already finished starting, 39 * {@link Future#get} returns immediately. 40 */ 41 Future<State> start(); 42 43 /** 44 * If the service is {@link State#STARTED} initiates service shutdown and 45 * returns immediately. If the service has already been stopped, this 46 * method returns immediately without taking action. 47 * 48 * @return a future for the shutdown result, regardless of whether this call 49 * initiated shutdown. Calling {@link Future#get} will block until the 50 * service has finished shutting down, and either returns {@link 51 * State#STOPPED} or throws an {@link ExecutionException}. If it has 52 * already finished stopping, {@link Future#get} returns immediately. 53 */ 54 Future<State> stop(); 55 56 /** 57 * Returns the current state of this service. One of {@link State} possible 58 * values, or null if this is a brand new object, i.e., has not been put into 59 * any state yet. 60 */ 61 State state(); 62 63 /** 64 * The lifecycle states of a service. 65 */ 66 enum State { STARTED, STOPPED, FAILED } 67 } 68
