Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 org.apache.commons.daemon; /** * Provides support for native daemon invocation. Using * a platform dependant helper program, classes that implement the * <code>Daemon</code> interface can be initialized, started and * stopped according to the conventions of the underlying operating * system. * <p> * Implementors of this interface must also provide a public constructor * with no arguments so that instances can be created in an automated * fashion. * </p> * @author Pier Fumagalli * @version $Id: Daemon.java 1204010 2011-11-19 16:15:23Z ggregory $ */ public interface Daemon { /** * Initializes this <code>Daemon</code> instance. * <p> * This method gets called once the JVM process is created and the * <code>Daemon</code> instance is created thru its empty public * constructor. * </p> * <p> * Under certain operating systems (typically Unix based operating * systems) and if the native invocation framework is configured to do * so, this method might be called with <i>super-user</i> privileges. * </p> * <p> * For example, it might be wise to create <code>ServerSocket</code> * instances within the scope of this method, and perform all operations * requiring <i>super-user</i> privileges in the underlying operating * system. * </p> * <p> * Apart from set up and allocation of native resources, this method * must not start the actual operation of the <code>Daemon</code> (such * as starting threads calling the <code>ServerSocket.accept()</code> * method) as this would impose some serious security hazards. The * start of operation must be performed in the <code>start()</code> * method. * </p> * * @param context A <code>DaemonContext</code> object used to * communicate with the container. * @exception DaemonInitException An exception that prevented * initialization where you want to display a nice message to the user, * rather than a stack trace. * @exception Exception Any exception preventing a successful * initialization. */ public void init(DaemonContext context) throws DaemonInitException, Exception; /** * Starts the operation of this <code>Daemon</code> instance. This * method is to be invoked by the environment after the init() * method has been successfully invoked and possibly the security * level of the JVM has been dropped. Implementors of this * method are free to start any number of threads, but need to * return control after having done that to enable invocation of * the stop()-method. */ public void start() throws Exception; /** * Stops the operation of this <code>Daemon</code> instance. Note * that the proper place to free any allocated resources such as * sockets or file descriptors is in the destroy method, as the * container may restart the Daemon by calling start() after * stop(). */ public void stop() throws Exception; /** * Frees any resources allocated by this daemon such as file * descriptors or sockets. This method gets called by the container * after stop() has been called, before the JVM exits. The Daemon * can not be restarted after this method has been called without a * new call to the init() method. */ public void destroy(); }