Servlet基础编程

编写Servlet

建立Servlet

这个类继承javax.servlet.http.HttpServlet

import javax.servlet.http.HttpServlet;public class WelcomeServlet extends HttpServlet {}

重写HttpServlet的doGet()方法

package xxx.xxx.servlets;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;//WelcomeServlet.javapublic class WelcomeServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {        response.setContentType("text/html;charset=GB18030");        PrintWriter out = response.getWriter();        out.println("欢迎来到本系统!");    }}

配置Servlet

<servlet>    <!-- servlet-name必须一样 -->    <servlet-name>WelcomeServlet</servlet-name>    <servlet-class>xxx.xxx.servlets.WelcomeServlet</servlet-class></servlet><servlet-mapping>  <servlet-name>WelcomeServlet</servlet-name>  <!-- url-pattern可以自己改，不一定一样 -->  <url-pattern>/servlets/WelcomeServlet</url-pattern></servlet-mapping>

配置好的web.xml:

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  <display-name>Servlet_1000</display-name>  <welcome-file-list>    <welcome-file>index.html</welcome-file>    <welcome-file>index.htm</welcome-file>    <welcome-file>index.jsp</welcome-file>    <welcome-file>default.html</welcome-file>    <welcome-file>default.htm</welcome-file>    <welcome-file>default.jsp</welcome-file>  </welcome-file-list>  <servlet>    <!-- servlet-name必须一样 -->    <servlet-name>WelcomeServlet</servlet-name>    <servlet-class>xxx.xxx.servlets.WelcomeServlet</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>WelcomeServlet</servlet-name>    <!-- url-pattern可以自己改，不一定一样 -->    <url-pattern>/servlets/WelcomeServlet</url-pattern>  </servlet-mapping></web-app>

部署Servlet

测试Servlet

Servlet运行机制

将WelcomeServlet.java改为如下：

public class WelcomeServlet extends HttpServlet {    public WelcomeServlet() {        System.out.println("创建对象!");    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {        System.out.println("调用doGet()函数!");        response.setContentType("text/html;charset=GB18030");        PrintWriter out = response.getWriter();        out.println("欢迎来到本系统!");    }}

重新部署项目，第一次访问WelcomeServlet，系统实例化WelcomeServlet对象，控制台打印如下：

第二次访问WelcomeServlet，控制台打印如下：

解释：第一次访问运行了构造函数和doGet()函数，第二次访问只运行了doGet()函数。
结论：两次访问只创建了一个Servlet对象。

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Servlet生命周期

1. init()：实例化Servlet。
2. doGet()/doPost()/service()方法：客户端对Servlet发送一个请求过来，服务器将会开启一个线程，该线程用service()方法，service()方法会根据收到的客户端的请求类型来决定是调用doGet()还是doPost()。但是一般情况下不用覆盖service()方法，使用doGet()与doPost()方法，一样可以达到处理的目的。
3. destroy()方法：Servlet消亡。

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Servlet与JSP内置对象

1. 获得out对象：

response.setContentType("text/html;charset=GB18030");//设置中文编码PrintWriter out = response.getWriter();

1. 获得request和response对象：request参数就是request对象，response参数就是response对象。
2. 获得session对象：

HttpSession session = request.getSession();

1. 获得application对象：

ServletContext application = this.getServletContext();

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设置欢迎页面

<welcome-file-list>   <!-- 所要设置的欢迎页面 -->   <welcome-file>index.html</welcome-file>   <welcome-file>index.jsp</welcome-file></welcome-file-list>

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在Servlet中读取参数

设置参数

配置好的web.xml：

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  <display-name>Servlet_1000</display-name>  <welcome-file-list>    <welcome-file>index.html</welcome-file>    <welcome-file>index.htm</welcome-file>    <welcome-file>index.jsp</welcome-file>    <welcome-file>default.html</welcome-file>    <welcome-file>default.htm</welcome-file>    <welcome-file>default.jsp</welcome-file>  </welcome-file-list>  <!-- 设置全局参数 -->  <context-param>    <param-name>encoding</param-name>    <param-value>GB18030</param-value>  </context-param>  <servlet>    <servlet-name>InitServlet</servlet-name>    <servlet-class>xxx.xxx.servlets.InitServlet</servlet-class>    <!-- 设置局部参数 -->    <init-param>        <param-name>driverClassName</param-name>        <param-value>com.mysql.jdbc.Driver</param-value>    </init-param>  </servlet>  <servlet-mapping>    <servlet-name>InitServlet</servlet-name>    <url-pattern>/servlets/InitServlet</url-pattern>  </servlet-mapping>  <servlet>    <!-- servlet-name必须一样 -->    <servlet-name>WelcomeServlet</servlet-name>    <servlet-class>xxx.xxx.servlets.WelcomeServlet</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>WelcomeServlet</servlet-name>    <!-- url-pattern可以自己改，不一定一样 -->    <url-pattern>/servlets/WelcomeServlet</url-pattern>  </servlet-mapping></web-app>

获取参数

InitServlet.java：

package xxx.xxx.servlets;import javax.servlet.ServletContext;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class InitServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) {        //获取全局参数        ServletContext application = this.getServletContext();        String encoding = application.getInitParameter("encoding");        System.out.println("encoding参数是："+encoding);        //获取局部参数        String driverClassName = this.getInitParameter("driverClassName");        System.out.println("driverClassName参数是："+driverClassName);    }}