javax.servlet.GenericServlet Maven / Gradle / Ivy
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/*
* 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.
*
* 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.
*/
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
* init 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 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) {
return getServletConfig().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() {
return getServletConfig().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() {
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}.
*
* 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 {
// 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 String 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
* 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() {
return config.getServletName();
}
}