/*
* 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 javax.servlet;
import java.io.IOException;
import java.util.Enumeration;
/**
* Defines a generic, protocol-independent
* servlet. To write an HTTP servlet for use on the
* Web, extend {@link javax.servlet.http.HttpServlet} instead.
* <p/>
* <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/>
* <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/>
* <p>To write a generic servlet, you need only
* override the abstract <code>service</code> method.
*
* @version $Rev$ $Date$
*/
public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable {
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/>
* <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) {
return getServletConfig().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/>
* <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() {
return getServletConfig().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/>
* <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() {
return getServletConfig().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/>
* <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 configutation
* information for this servlet
* @throws ServletException if an exception occurs that
* interrupts the servlet's normal
* operation
* @see UnavailableException
*/
public void init(ServletConfig config) throws ServletException {
this.config = config;
init();
}
/**
* A convenience method which can be overridden so that there's no need
* to call <code>super.init(config)</code>.
* <p/>
* <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}.
*
* @throws 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/>
* <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
* @throws ServletException if an exception occurs that
* interferes with the servlet's
* normal operation occurred
* @throws 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() {
return config.getServletName();
}
}