先来简单的例子吧。大概如下：index.jsp页面中只有一个按钮，用来跳转到Servlet操作数据，Servlet中对数据库查询操作后将信息保存在request对象中通过转发传递到showinfo.jsp页面（如果你对数据的操作也是在jsp中，java代码逻辑部分其实是一样的，注意跳转路径即可；用了@Controllor同理，跳转的逻辑也是一样的）
把数据库建好
CREATE TABLE `User` (`id` int(11) NOT NULL,`username` varchar(255) DEFAULT NULL,`password` varchar(255) DEFAULT NULL,`address` varchar(255) DEFAULT NULL,PRIMARY KEY (`id`))
插入一个数据
insert into User values(1,"Martin","12345","zjut")
建立一个Dynamic Web Project，目录如下：
User.java
package com.entity;public class User {private int id;private String username;private String password;private String address;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}@Overridepublic String toString() {return "User [id=" + id + ", username=" + username + ", password=" + password + ", address=" + address + "]";}public User(int id, String username, String password, String address) {super();this.id = id;this.username = username;this.password = password;this.address = address;}public User() {super();}}
DBHelper.java
package com.utils;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;public class DBHelper {private static final String driver = "com.mysql.cj.jdbc.Driver";private static final String url = "jdbc:mysql://localhost:3306/webtest?useUnicode=true&characterEncoding=UTF-8";private static final String username = "root";private static final String password = "123456";private static Connection conn=null;static {try {Class.forName(driver);} catch (ClassNotFoundException e) {e.printStackTrace();}}public static Connection getConnection() {if(conn==null) {try {conn = DriverManager.getConnection(url,username,password);System.out.println("数据库初始化成功");} catch (SQLException e) {e.printStackTrace();System.out.println("数据库初始化失败");}return conn;}else {return conn;}}}
ServletDemo.java
package com.servlet;import java.io.IOException;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.entity.User;import com.utils.DBHelper;@WebServlet("/servlet/ServletDemo")public class ServletDemo extends HttpServlet {private static final long serialVersionUID = 1L;public ServletDemo() {super();}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {Connection conn = DBHelper.getConnection();String sql="select * from User";try {Statement st = conn.createStatement();ResultSet rs = st.executeQuery(sql);User user = new User();while(rs.next()) {user.setId(rs.getInt("id"));user.setUsername(rs.getString("username"));user.setPassword(rs.getString("password"));user.setAddress(rs.getString("address"));}//将数据库中查询到的信息封装在user对象中，use对象保存在request中，之后将通过request对象将数据传递到页面//需要的话也可以只传递一个参数request.setAttribute("id", user.getId());request.setAttribute("user", user);//这里是转发，从Servlet跳转到showinfo.jsp页面，并且带上request和response对象中原有的参数request.getRequestDispatcher("/showinfo.jsp").forward(request, response);} catch (SQLException e) {e.printStackTrace();}}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}
这里用的是转发，可以保存request对象中的数据；至于重定向则是另外一个新的request，所以原有的数据会消失，在jsp获取不到。
index.jsp，只一个按钮
<body><form action="servlet/ServletDemo" method="get"><input type="submit" ></form></body>
showinfo.jsp，这里需要注意的是导入类：import="com.entity.User"
<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8" import="com.entity.User"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body><%User user = (User)request.getAttribute("user");%>id:<%=user.getId() %>username:<%=user.getUsername() %>password:<%=user.getPassword() %>address:<%=user.getAddress() %><!-- 也可以用el表达式，但是同样需要servlet先将值存放在request中，但是用el表达式的话需要在上面加上：<%@ taglib uri="/jsp/jstl/core" prefix="c"%>如下，获取id这样写就可以${user.getId()}--></body></html>
启动tomcat操作点击按钮即可结果如下
ps:分界线以上是原创，以下是在某原博主的内容之后的补充
转载原文及源代码链接：/qq_23994787/article/details/73612870
showall.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%> <%@ taglib uri="/jsp/jstl/core" prefix="c"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><base href="<%=basePath%>"><title>所有用户页面</title></head><body><h1>${xiaoxi}</h1><table width="600" border="1" cellpadding="0" ><tr><th>ID</th><th>姓名</th><th>性别</th><th>密码</th><th>家乡</th><th>备注</th><th>操作</th></tr><c:forEach var="U" items="${userAll}" > <form action="UpdateServlet" method="post"><tr><td><input type="text" value="${U.id}" name="id" ></td><td><input type="text" value="${U.name}" name="name"></td><td><input type="text" value="${U.sex}" name="sex"></td><td><input type="text" value="${U.pwd}" name="pwd"></td><td><input type="text" value="${U.home}" name="home"></td><td><input type="text" value="${U.info}" name="info"></td><td><a href="DeleteServlet?id=${U.id}">删除</a> <input type="submit" value="更新"/></td></tr></form></c:forEach> </table></body></html>
SearchAllServlet.java程序如下,导包之类的略
public class SearchAllServlet extends HttpServlet{@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoPost(request,response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubUserDao ud = new UserDaoImpl();List<User> userAll = ud.getUserAll();request.setAttribute("userAll", userAll);request.getRequestDispatcher("/showall.jsp").forward(request, response);}}
数据库查询到的所有用户数据保存在List集合userAll中，通过request.setAttribute("userAll",userAll)传入jsp
jsp通过<c:forEach var="U" items="${userAll}" >取出数据并进行遍历
以上，需要注意的是showall中用到了<c:forEach>标签，并且传值的时候使用了el表达式${...}，因此还需要导入包jstl.jar和standard.jar并且在showall.jsp中增加：
<%@ taglib uri="/jsp/jstl/core" prefix="c"%>
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