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/* * Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved. * Copyright 2004 The Apache Software Foundation * * 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 javax.servlet; import java.io.IOException; import java.util.Enumeration; import java.util.ResourceBundle; /** * * Defines a generic, protocol-independent * servlet. To write an HTTP servlet for use on the * Web, extend {@link javax.servlet.http.HttpServlet} instead. * * <p><code>GenericServlet</code> implements the <code>Servlet</code> * and <code>ServletConfig</code> interfaces. <code>GenericServlet</code> * may be directly extended by a servlet, although it's more common to extend * a protocol-specific subclass such as <code>HttpServlet</code>. * * <p><code>GenericServlet</code> makes writing servlets * easier. It provides simple versions of the lifecycle methods * <code>init</code> and <code>destroy</code> and of the methods * in the <code>ServletConfig</code> interface. <code>GenericServlet</code> * also implements the <code>log</code> method, declared in the * <code>ServletContext</code> interface. * * <p>To write a generic servlet, you need only * override the abstract <code>service</code> method. * * * @author Various */ public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable { private static final String LSTRING_FILE = "javax.servlet.LocalStrings"; private static ResourceBundle lStrings = ResourceBundle.getBundle(LSTRING_FILE); private transient ServletConfig config; /** * * Does nothing. All of the servlet initialization * is done by one of the <code>init</code> methods. * */ public GenericServlet() { } /** * Called by the servlet container to indicate to a servlet that the * servlet is being taken out of service. See {@link Servlet#destroy}. * * */ public void destroy() { } /** * Returns a <code>String</code> containing the value of the named * initialization parameter, or <code>null</code> if the parameter does * not exist. See {@link ServletConfig#getInitParameter}. * * <p>This method is supplied for convenience. It gets the * value of the named parameter from the servlet's * <code>ServletConfig</code> object. * * @param name a <code>String</code> specifying the name * of the initialization parameter * * @return String a <code>String</code> containing the value * of the initialization parameter * */ public String getInitParameter(String name) { ServletConfig sc = getServletConfig(); if (sc == null) { throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized")); } return sc.getInitParameter(name); } /** * Returns the names of the servlet's initialization parameters * as an <code>Enumeration</code> of <code>String</code> objects, * or an empty <code>Enumeration</code> if the servlet has no * initialization parameters. See {@link * ServletConfig#getInitParameterNames}. * * <p>This method is supplied for convenience. It gets the * parameter names from the servlet's <code>ServletConfig</code> object. * * * @return Enumeration an enumeration of <code>String</code> * objects containing the names of * the servlet's initialization parameters */ public Enumeration<String> getInitParameterNames() { ServletConfig sc = getServletConfig(); if (sc == null) { throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized")); } return sc.getInitParameterNames(); } /** * Returns this servlet's {@link ServletConfig} object. * * @return ServletConfig the <code>ServletConfig</code> object * that initialized this servlet */ public ServletConfig getServletConfig() { return config; } /** * Returns a reference to the {@link ServletContext} in which this servlet * is running. See {@link ServletConfig#getServletContext}. * * <p>This method is supplied for convenience. It gets the * context from the servlet's <code>ServletConfig</code> object. * * * @return ServletContext the <code>ServletContext</code> object * passed to this servlet by the <code>init</code> * method */ public ServletContext getServletContext() { ServletConfig sc = getServletConfig(); if (sc == null) { throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized")); } return sc.getServletContext(); } /** * Returns information about the servlet, such as * author, version, and copyright. * By default, this method returns an empty string. Override this method * to have it return a meaningful value. See {@link * Servlet#getServletInfo}. * * * @return String information about this servlet, by default an * empty string */ public String getServletInfo() { return ""; } /** * Called by the servlet container to indicate to a servlet that the * servlet is being placed into service. See {@link Servlet#init}. * * <p>This implementation stores the {@link ServletConfig} * object it receives from the servlet container for later use. * When overriding this form of the method, call * <code>super.init(config)</code>. * * @param config the <code>ServletConfig</code> object * that contains configuration * information for this servlet * * @exception ServletException if an exception occurs that * interrupts the servlet's normal * operation * * @see UnavailableException */ public void init(ServletConfig config) throws ServletException { this.config = config; this.init(); } /** * A convenience method which can be overridden so that there's no need * to call <code>super.init(config)</code>. * * <p>Instead of overriding {@link #init(ServletConfig)}, simply override * this method and it will be called by * <code>GenericServlet.init(ServletConfig config)</code>. * The <code>ServletConfig</code> object can still be retrieved via {@link * #getServletConfig}. * * @exception ServletException if an exception occurs that * interrupts the servlet's * normal operation */ public void init() throws ServletException { } /** * Writes the specified message to a servlet log file, prepended by the * servlet's name. See {@link ServletContext#log(String)}. * * @param msg a <code>String</code> specifying * the message to be written to the log file */ public void log(String msg) { getServletContext().log(getServletName() + ": " + msg); } /** * Writes an explanatory message and a stack trace * for a given <code>Throwable</code> exception * to the servlet log file, prepended by the servlet's name. * See {@link ServletContext#log(String, Throwable)}. * * * @param message a <code>String</code> that describes * the error or exception * * @param t the <code>java.lang.Throwable</code> error * or exception */ public void log(String message, Throwable t) { getServletContext().log(getServletName() + ": " + message, t); } /** * Called by the servlet container to allow the servlet to respond to * a request. See {@link Servlet#service}. * * <p>This method is declared abstract so subclasses, such as * <code>HttpServlet</code>, must override it. * * @param req the <code>ServletRequest</code> object * that contains the client's request * * @param res the <code>ServletResponse</code> object * that will contain the servlet's response * * @exception ServletException if an exception occurs that * interferes with the servlet's * normal operation occurred * * @exception IOException if an input or output * exception occurs */ public abstract void service(ServletRequest req, ServletResponse res) throws ServletException, IOException; /** * Returns the name of this servlet instance. * See {@link ServletConfig#getServletName}. * * @return the name of this servlet instance */ public String getServletName() { ServletConfig sc = getServletConfig(); if (sc == null) { throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized")); } return sc.getServletName(); } }