javax.servlet.GenericServlet Maven / Gradle / Ivy
/*
* Copyright (c) 1997-2018 Oracle and/or its affiliates and others.
* 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.
*
*
* GenericServlet implements the Servlet and ServletConfig interfaces.
* GenericServlet may be directly extended by a servlet, although it's more common to extend a
* protocol-specific subclass such as HttpServlet.
*
*
* GenericServlet makes writing servlets easier. It provides simple versions of the lifecycle methods
* init and destroy and of the methods in the ServletConfig interface.
* GenericServlet also implements the log method, declared in the ServletContext
* interface.
*
*
* To write a generic servlet, you need only override the abstract service method.
*
*
* @author Various
*/
public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable {
private static final long serialVersionUID = -8592279577370996712L;
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 init 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}.
*
*
*/
@Override
public void destroy() {
}
/**
* Returns a String containing the value of the named initialization parameter, or null if
* the parameter does not exist. See {@link ServletConfig#getInitParameter}.
*
*
* This method is supplied for convenience. It gets the value of the named parameter from the servlet's
* ServletConfig object.
*
* @param name a String specifying the name of the initialization parameter
*
* @return String a String containing the value of the initialization parameter
*
*/
@Override
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 Enumeration of
* String objects, or an empty Enumeration if the servlet has no initialization
* parameters. See {@link ServletConfig#getInitParameterNames}.
*
*
* This method is supplied for convenience. It gets the parameter names from the servlet's
* ServletConfig object.
*
*
* @return Enumeration an enumeration of String objects containing the names of the servlet's
* initialization parameters
*/
@Override
public Enumeration 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 ServletConfig object that initialized this servlet
*/
@Override
public ServletConfig getServletConfig() {
return config;
}
/**
* Returns a reference to the {@link ServletContext} in which this servlet is running. See
* {@link ServletConfig#getServletContext}.
*
*
* This method is supplied for convenience. It gets the context from the servlet's ServletConfig
* object.
*
*
* @return ServletContext the ServletContext object passed to this servlet by the init
* method
*/
@Override
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
*/
@Override
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}.
*
*
* This implementation stores the {@link ServletConfig} object it receives from the servlet container for later use.
* When overriding this form of the method, call super.init(config).
*
* @param config the ServletConfig object that contains configuration information for this servlet
*
* @exception ServletException if an exception occurs that interrupts the servlet's normal operation
*
* @see UnavailableException
*/
@Override
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 super.init(config).
*
*
* Instead of overriding {@link #init(ServletConfig)}, simply override this method and it will be called by
* GenericServlet.init(ServletConfig config). The ServletConfig 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 String 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 Throwable exception to the servlet log
* file, prepended by the servlet's name. See {@link ServletContext#log(String, Throwable)}.
*
*
* @param message a String that describes the error or exception
*
* @param t the java.lang.Throwable 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}.
*
*
* This method is declared abstract so subclasses, such as HttpServlet, must override it.
*
* @param req the ServletRequest object that contains the client's request
*
* @param res the ServletResponse 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
*/
@Override
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
*/
@Override
public String getServletName() {
ServletConfig sc = getServletConfig();
if (sc == null) {
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getServletName();
}
}