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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 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}. * * */ 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 * */ 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 */ 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 */ 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 */ 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}. * *

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 configutation * 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 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 */ 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(); } }





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