001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018 package org.apache.commons.daemon; 019 020 /** 021 * This interface provides support for native daemon invocation. Using 022 * a platform dependant helper program classes that implement the 023 * <code>Daemon</code> interface can be initialized, started and 024 * stopped according to the convensions of the underlying operating 025 * system. 026 * <p> 027 * Implementors of this interface must also provide a public constructor 028 * with no arguments so that instances can be created in an automated 029 * fashion. 030 * </p> 031 * @author Pier Fumagalli 032 * @version 1.0 <i>(CVS $Revision: 557416 $)</i> 033 */ 034 public interface Daemon { 035 036 /** 037 * Initialize this <code>Daemon</code> instance. 038 * <p> 039 * This method gets called once the JVM process is created and the 040 * <code>Daemon</code> instance is created thru its empty public 041 * constructor. 042 * </p> 043 * <p> 044 * Under certain operating systems (typically Unix based operating 045 * systems) and if the native invocation framework is configured to do 046 * so, this method might be called with <i>super-user</i> privileges. 047 * </p> 048 * <p> 049 * For example, it might be wise to create <code>ServerSocket</code> 050 * instances within the scope of this method, and perform all operations 051 * requiring <i>super-user</i> privileges in the underlying operating 052 * system. 053 * </p> 054 * <p> 055 * Apart from set up and allocation of native resources, this method 056 * must not start the actual operation of the <code>Daemon</code> (such 057 * as starting threads calling the <code>ServerSocket.accept()</code> 058 * method) as this would impose some serious security hazards. The 059 * start of operation must be performed in the <code>start()</code> 060 * method. 061 * </p> 062 * 063 * @param context A <code>DaemonContext</code> object used to 064 * communicate with the container. 065 * 066 * @exception Exception Any exception preventing a successful 067 * initialization. 068 */ 069 public void init(DaemonContext context) 070 throws Exception; 071 072 /** 073 * Start the operation of this <code>Daemon</code> instance. This 074 * method is to be invoked by the environment after the init() 075 * method has been successfully invoked and possibly the security 076 * level of the JVM has been dropped. Implementors of this 077 * method are free to start any number of threads, but need to 078 * return control after having done that to enable invocation of 079 * the stop()-method. 080 */ 081 public void start() 082 throws Exception; 083 084 /** 085 * Stop the operation of this <code>Daemon</code> instance. Note 086 * that the proper place to free any allocated resources such as 087 * sockets or file descriptors is in the destroy method, as the 088 * container may restart the Daemon by calling start() after 089 * stop(). 090 */ 091 public void stop() 092 throws Exception; 093 094 /** 095 * Free any resources allocated by this daemon such as file 096 * descriptors or sockets. This method gets called by the container 097 * after stop() has been called, before the JVM exits. The Daemon 098 * can not be restarted after this method has been called without a 099 * new call to the init() method. 100 */ 101 public void destroy(); 102 }