GenericServlet.java
/*
* 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>
* <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.
*/
public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable {
private static final long serialVersionUID = 1L;
private transient ServletConfig config;
/**
* Does nothing. All of the servlet initialization is done by one of the <code>init</code> methods.
*/
public GenericServlet() {
// NOOP
}
/**
* 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() {
// NOOP by default
}
/**
* 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
*/
@Override
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>
* 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
*/
@Override
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
*/
@Override
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
*/
@Override
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
*/
@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}.
* <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
*/
@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 <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 {
// NOOP by default
}
/**
* Writes the specified message to a servlet log file, prepended by the servlet's name. See
* {@link ServletContext#log(String)}.
*
* @param message a <code>String</code> specifying the message to be written to the log file
*/
public void log(String message) {
getServletContext().log(getServletName() + ": " + message);
}
/**
* 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
*/
@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() {
return config.getServletName();
}
}