Servlet（Server Applet）是Java Servlet的簡稱，稱為服務器端小程序，用Java代碼進行編寫，具有獨立于平臺和協議的特性，主要功能在于交互式地瀏覽和生成數據，生成動態Web內容。

Servlet是指任何實現了這個Servlet接口的類，運行于支持Java的應用服務器中。

文章目錄

• • Servlet使用步驟

源碼：

/** 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.** <p>* 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.** <p>* To implement this interface, you can write a generic servlet that extends* <code>javax.servlet.GenericServlet</code> or an HTTP servlet that extends* <code>javax.servlet.http.HttpServlet</code>.** <p>* 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:* <ol>* <li>The servlet is constructed, then initialized with the <code>init</code>* method.* <li>Any calls from clients to the <code>service</code> method are handled.* <li>The servlet is taken out of service, then destroyed with the* <code>destroy</code> method, then garbage collected and finalized.* </ol>** <p>* In addition to the life-cycle methods, this interface provides the* <code>getServletConfig</code> method, which the servlet can use to get any* startup information, and the <code>getServletInfo</code> 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.** <p>* The servlet container calls the <code>init</code> method exactly once* after instantiating the servlet. The <code>init</code> method must* complete successfully before the servlet can receive any requests.** <p>* The servlet container cannot place the servlet into service if the* <code>init</code> method* <ol>* <li>Throws a <code>ServletException</code>* <li>Does not return within a time period defined by the Web server* </ol>*** @param config* a <code>ServletConfig</code> 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;//對象的初始化創建/**** Returns a {@link ServletConfig} object, which contains initialization and* startup parameters for this servlet. The <code>ServletConfig</code>* object returned is the one passed to the <code>init</code> method.** <p>* Implementations of this interface are responsible for storing the* <code>ServletConfig</code> object so that this method can return it. The* {@link GenericServlet} class, which implements this interface, already* does this.** @return the <code>ServletConfig</code> object that initializes this* servlet** @see #init*/public ServletConfig getServletConfig();//拿到當前web對象的配置文件/*** Called by the servlet container to allow the servlet to respond to a* request.** <p>* This method is only called after the servlet's <code>init()</code> method* has completed successfully.** <p>* The status code of the response always should be set for a servlet that* throws or sends an error.*** <p>* 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 <a* href* ="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">* the Java tutorial on multi-threaded programming</a>.*** @param req* the <code>ServletRequest</code> object that contains the* client's request** @param res* the <code>ServletResponse</code> 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.** <p>* The string that this method returns should be plain text and not markup* of any kind (such as HTML, XML, etc.).** @return a <code>String</code> containing servlet information*/public String getServletInfo();//當前servlet的基本信息/*** 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 <code>service</code> method have exited or* after a timeout period has passed. After the servlet container calls this* method, it will not call the <code>service</code> method again on this* servlet.** <p>* 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();//對象銷毀 }

Servlet使用步驟

編寫?個Java類實現Servlet的接口

在web.xml中，配置Servlet

訪問servlet

//1. 編寫?個Java類實現Servlet的接口import java.io.IOException;import javax.servlet.Servlet; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse;public class HelloServlet implements Servlet {@Overridepublic void init(ServletConfig config) throws ServletException {}@Overridepublic ServletConfig getServletConfig() {return null;}@Override /*** ?來處理客戶的請求，并且對請求作出響應的?法*/public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {System.out.println("?個servlet程序。。");//把服務器的數據 返回給瀏覽器顯示// 向??輸出?個HelloServlet字符串:servletResponse.getWriter().print("<font color='red'>hello servlet</font>");}@Overridepublic String getServletInfo() {return null;}@Overridepublic void destroy() {}//省略剩下?法，采?默認實現 } //2. 在web.xml中，配置Servlet <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><servlet><servlet-name>helloServlet</servlet-name><servlet-class>com.byc.servlet.HelloServlet</servlet-class></servlet><servlet-mapping><servlet-name>helloServlet</servlet-name><url-pattern>/hello</url-pattern> <!--匹配路徑--></servlet-mapping> </web-app>

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