init
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java/javax/servlet/GenericServlet.java
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238
java/javax/servlet/GenericServlet.java
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package javax.servlet;
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import java.io.IOException;
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import java.util.Enumeration;
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/**
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* Defines a generic, protocol-independent servlet. To write an HTTP servlet for
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* use on the Web, extend {@link javax.servlet.http.HttpServlet} instead.
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* <p>
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* <code>GenericServlet</code> implements the <code>Servlet</code> and
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* <code>ServletConfig</code> interfaces. <code>GenericServlet</code> may be
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* directly extended by a servlet, although it's more common to extend a
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* protocol-specific subclass such as <code>HttpServlet</code>.
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* <p>
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* <code>GenericServlet</code> makes writing servlets easier. It provides simple
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* versions of the lifecycle methods <code>init</code> and <code>destroy</code>
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* and of the methods in the <code>ServletConfig</code> interface.
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* <code>GenericServlet</code> also implements the <code>log</code> method,
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* declared in the <code>ServletContext</code> interface.
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* <p>
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* To write a generic servlet, you need only override the abstract
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* <code>service</code> method.
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*/
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public abstract class GenericServlet implements Servlet, ServletConfig,
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java.io.Serializable {
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private static final long serialVersionUID = 1L;
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private transient ServletConfig config;
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/**
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* Does nothing. All of the servlet initialization is done by one of the
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* <code>init</code> methods.
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*/
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public GenericServlet() {
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// NOOP
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}
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/**
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* Called by the servlet container to indicate to a servlet that the servlet
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* is being taken out of service. See {@link Servlet#destroy}.
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*/
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@Override
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public void destroy() {
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// NOOP by default
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}
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/**
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* Returns a <code>String</code> containing the value of the named
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* initialization parameter, or <code>null</code> if the parameter does not
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* exist. See {@link ServletConfig#getInitParameter}.
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* <p>
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* This method is supplied for convenience. It gets the value of the named
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* parameter from the servlet's <code>ServletConfig</code> object.
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*
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* @param name
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* a <code>String</code> specifying the name of the
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* initialization parameter
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* @return String a <code>String</code> containing the value of the
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* initialization parameter
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*/
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@Override
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public String getInitParameter(String name) {
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return getServletConfig().getInitParameter(name);
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}
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/**
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* Returns the names of the servlet's initialization parameters as an
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* <code>Enumeration</code> of <code>String</code> objects, or an empty
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* <code>Enumeration</code> if the servlet has no initialization parameters.
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* See {@link ServletConfig#getInitParameterNames}.
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* <p>
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* This method is supplied for convenience. It gets the parameter names from
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* the servlet's <code>ServletConfig</code> object.
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*
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* @return Enumeration an enumeration of <code>String</code> objects
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* containing the names of the servlet's initialization parameters
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*/
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@Override
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public Enumeration<String> getInitParameterNames() {
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return getServletConfig().getInitParameterNames();
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}
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/**
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* Returns this servlet's {@link ServletConfig} object.
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*
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* @return ServletConfig the <code>ServletConfig</code> object that
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* initialized this servlet
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*/
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@Override
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public ServletConfig getServletConfig() {
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return config;
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}
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/**
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* Returns a reference to the {@link ServletContext} in which this servlet
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* is running. See {@link ServletConfig#getServletContext}.
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* <p>
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* This method is supplied for convenience. It gets the context from the
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* servlet's <code>ServletConfig</code> object.
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*
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* @return ServletContext the <code>ServletContext</code> object passed to
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* this servlet by the <code>init</code> method
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*/
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@Override
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public ServletContext getServletContext() {
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return getServletConfig().getServletContext();
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}
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/**
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* Returns information about the servlet, such as author, version, and
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* copyright. By default, this method returns an empty string. Override this
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* method to have it return a meaningful value. See
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* {@link Servlet#getServletInfo}.
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*
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* @return String information about this servlet, by default an empty string
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*/
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@Override
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public String getServletInfo() {
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return "";
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}
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/**
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* Called by the servlet container to indicate to a servlet that the servlet
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* is being placed into service. See {@link Servlet#init}.
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* <p>
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* This implementation stores the {@link ServletConfig} object it receives
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* from the servlet container for later use. When overriding this form of
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* the method, call <code>super.init(config)</code>.
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*
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* @param config
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* the <code>ServletConfig</code> object that contains
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* configuration information for this servlet
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* @exception ServletException
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* if an exception occurs that interrupts the servlet's
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* normal operation
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* @see UnavailableException
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*/
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@Override
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public void init(ServletConfig config) throws ServletException {
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this.config = config;
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this.init();
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}
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/**
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* A convenience method which can be overridden so that there's no need to
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* call <code>super.init(config)</code>.
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* <p>
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* Instead of overriding {@link #init(ServletConfig)}, simply override this
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* method and it will be called by
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* <code>GenericServlet.init(ServletConfig config)</code>. The
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* <code>ServletConfig</code> object can still be retrieved via
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* {@link #getServletConfig}.
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*
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* @exception ServletException
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* if an exception occurs that interrupts the servlet's
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* normal operation
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*/
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public void init() throws ServletException {
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// NOOP by default
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}
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/**
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* Writes the specified message to a servlet log file, prepended by the
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* servlet's name. See {@link ServletContext#log(String)}.
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*
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* @param msg
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* a <code>String</code> specifying the message to be written to
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* the log file
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*/
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public void log(String msg) {
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getServletContext().log(getServletName() + ": " + msg);
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}
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/**
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* Writes an explanatory message and a stack trace for a given
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* <code>Throwable</code> exception to the servlet log file, prepended by
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* the servlet's name. See {@link ServletContext#log(String, Throwable)}.
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*
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* @param message
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* a <code>String</code> that describes the error or exception
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* @param t
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* the <code>java.lang.Throwable</code> error or exception
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*/
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public void log(String message, Throwable t) {
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getServletContext().log(getServletName() + ": " + message, t);
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}
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/**
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* Called by the servlet container to allow the servlet to respond to a
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* request. See {@link Servlet#service}.
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* <p>
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* This method is declared abstract so subclasses, such as
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* <code>HttpServlet</code>, must override it.
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*
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* @param req
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* the <code>ServletRequest</code> object that contains the
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* client's request
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* @param res
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* the <code>ServletResponse</code> object that will contain the
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* servlet's response
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* @exception ServletException
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* if an exception occurs that interferes with the servlet's
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* normal operation occurred
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* @exception IOException
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* if an input or output exception occurs
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*/
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@Override
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public abstract void service(ServletRequest req, ServletResponse res)
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throws ServletException, IOException;
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/**
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* Returns the name of this servlet instance. See
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* {@link ServletConfig#getServletName}.
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*
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* @return the name of this servlet instance
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*/
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@Override
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public String getServletName() {
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return config.getServletName();
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}
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}
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