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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;

/**
 * Defines methods that all servlets must implement.
 *
 * 

* A servlet is a small Java program that runs within a Web server. Servlets * receive and respond to requests from Web clients, usually across HTTP, the * HyperText Transfer Protocol. * *

* To implement this interface, you can write a generic servlet that extends * javax.servlet.GenericServlet or an HTTP servlet that extends * javax.servlet.http.HttpServlet. * *

* This interface defines methods to initialize a servlet, to service requests, * and to remove a servlet from the server. These are known as life-cycle * methods and are called in the following sequence: *

    *
  1. The servlet is constructed, then initialized with the init * method. *
  2. Any calls from clients to the service method are handled. *
  3. The servlet is taken out of service, then destroyed with the * destroy method, then garbage collected and finalized. *
* *

* In addition to the life-cycle methods, this interface provides the * getServletConfig method, which the servlet can use to get any * startup information, and the getServletInfo method, which allows * the servlet to return basic information about itself, such as author, * version, and copyright. * * @see GenericServlet * @see javax.servlet.http.HttpServlet */ public interface Servlet { /** * Called by the servlet container to indicate to a servlet that the servlet * is being placed into service. * *

* The servlet container calls the init method exactly once * after instantiating the servlet. The init method must * complete successfully before the servlet can receive any requests. * *

* The servlet container cannot place the servlet into service if the * init method *

    *
  1. Throws a ServletException *
  2. Does not return within a time period defined by the Web server *
* * * @param config * a ServletConfig object containing the servlet's * configuration and initialization parameters * * @exception ServletException * if an exception has occurred that interferes with the * servlet's normal operation * * @see UnavailableException * @see #getServletConfig */ public void init(ServletConfig config) throws ServletException; /** * * Returns a {@link ServletConfig} object, which contains initialization and * startup parameters for this servlet. The ServletConfig * object returned is the one passed to the init method. * *

* Implementations of this interface are responsible for storing the * ServletConfig object so that this method can return it. The * {@link GenericServlet} class, which implements this interface, already * does this. * * @return the ServletConfig object that initializes this * servlet * * @see #init */ public ServletConfig getServletConfig(); /** * Called by the servlet container to allow the servlet to respond to a * request. * *

* This method is only called after the servlet's init() method * has completed successfully. * *

* The status code of the response always should be set for a servlet that * throws or sends an error. * * *

* Servlets typically run inside multithreaded servlet containers that can * handle multiple requests concurrently. Developers must be aware to * synchronize access to any shared resources such as files, network * connections, and as well as the servlet's class and instance variables. * More information on multithreaded programming in Java is available in * the Java tutorial on multi-threaded programming. * * * @param req * the ServletRequest object that contains the * client's request * * @param res * the ServletResponse object that contains the * servlet's response * * @exception ServletException * if an exception occurs that interferes with the servlet's * normal operation * * @exception IOException * if an input or output exception occurs */ public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException; /** * Returns information about the servlet, such as author, version, and * copyright. * *

* The string that this method returns should be plain text and not markup * of any kind (such as HTML, XML, etc.). * * @return a String containing servlet information */ public String getServletInfo(); /** * Called by the servlet container to indicate to a servlet that the servlet * is being taken out of service. This method is only called once all * threads within the servlet's service method have exited or * after a timeout period has passed. After the servlet container calls this * method, it will not call the service method again on this * servlet. * *

* This method gives the servlet an opportunity to clean up any resources * that are being held (for example, memory, file handles, threads) and make * sure that any persistent state is synchronized with the servlet's current * state in memory. */ public void destroy(); }





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