JavaEE_JavaScript__前台(Jsp页面) + 后台数据处理(Servlet)，与javaScript的过程的处理

来源：互联网发布：js三大家族编辑：程序博客网时间：2024/05/21 17:08

今天一直遇到一个问题，JSP利用JavaScript 函数将密码进行了清空，后台查看数据的时候，没有找到数据。

分析后的原因为：JavaScript 的代码执行的过程为提交表单之前，因为 javaScript的代码执行修改了表单数据，导致后台接收不到数据，代码如下：

<%--version  1.0Copyright (C), 2001-2016, yeeku.H.LeeThis program is protected by copyright laws.Program Name:Date: --%><%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title> 用户登录 </title><meta name="website" content="http://www.crazyit.org" /></head><body><!-- 输出出错提示 --><span style="color:red;font-weight:bold"><%if (request.getAttribute("err") != null){out.println(request.getAttribute("err") + "<br/>");}%></span>请输入用户名和密码：<!-- 登录表单，该表单提交到一个Servlet --><form id="login" method="post" action="login">用户名：<input type="text" name="username"/><br/>密  码：<input type="password" id="pass" name="pass"/><br/><input type="submit" value="登录" id="submitk"/><br/></form><script type="text/javascript">/* var clear = function(){if(document.getElementById("pass").value != null){//alert("清空密码");document.getElementById("pass").value = "";}}document.getElementById("submitk").onclick = clear; */</script></body></html>

后台Servlet 代码：

package lee;import java.io.IOException;import java.sql.ResultSet;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * Description: <br/> * 网站: <a href="http://www.crazyit.org">疯狂Java联盟</a> <br/> * Copyright (C), 2001-2016, Yeeku.H.Lee <br/> * This program is protected by copyright laws. <br/> * Program Name: <br/> * Date: *  * @author Yeeku.H.Lee kongyeeku@163.com * @version 1.0 */// @WebServlet(name = "login", urlPatterns = { "/login" })public class LoginServlet extends HttpServlet {// 响应客户端请求的方法public void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, java.io.IOException {String errMsg = "";// Servlet本身并不输出响应到客户端，因此必须将请求转发到视图页面RequestDispatcher rd;// 获取请求参数String username = request.getParameter("username");String pass = request.getParameter("pass");System.out.println("前台传递的密码:" + pass);try {// Servlet本身并不执行任何的业务逻辑处理，它调用JavaBean处理用户请求DbDao dd = new DbDao("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/liuyan", "root", "123456");// 查询结果集ResultSet rs = dd.query("select pass from user_inf"+ " where name = ?", username);if (rs.next()) {// 用户名和密码匹配System.out.println("数据库中的密码:" + rs.getString("pass"));// System.out.println(username + "---ssss");// System.out.println(pass + "---ssss");if (rs.getString("pass").equals(pass)) {// 获取session对象HttpSession session = request.getSession(true);// 设置session属性，跟踪用户会话状态session.setAttribute("name", username);// 获取转发对象rd = request.getRequestDispatcher("/welcome.jsp");// 转发请求rd.forward(request, response);} else {// 用户名和密码不匹配时errMsg += "您的用户名密码不符合,请重新输入";}} else {// 用户名不存在时errMsg += "您的用户名不存在,请先注册";}} catch (Exception e) {e.printStackTrace();}// 如果出错，转发到重新登录if (errMsg != null && !errMsg.equals("")) {rd = request.getRequestDispatcher("/login.jsp");request.setAttribute("err", errMsg);rd.forward(request, response);}}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {// TODO Auto-generated method stubString errMsg = "";// Servlet本身并不输出响应到客户端，因此必须将请求转发到视图页面RequestDispatcher rd;// 获取请求参数String username = req.getParameter("username");String pass = req.getParameter("pass");try {// Servlet本身并不执行任何的业务逻辑处理，它调用JavaBean处理用户请求DbDao dd = new DbDao("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/liuyan", "root", "123456");// 查询结果集ResultSet rs = dd.query("select pass from user_inf"+ " where name = ?", username);if (rs.next()) {// 用户名和密码匹配if (rs.getString("pass").equals(pass)) {// 获取session对象HttpSession session = req.getSession(true);// 设置session属性，跟踪用户会话状态session.setAttribute("name", username);// 获取转发对象rd = req.getRequestDispatcher("/welcome.jsp");// 转发请求rd.forward(req, resp);} else {// 用户名和密码不匹配时errMsg += "您的用户名密码不符合,请重新输入";}} else {// 用户名不存在时errMsg += "您的用户名不存在,请先注册";}} catch (Exception e) {e.printStackTrace();}// 如果出错，转发到重新登录if (errMsg != null && !errMsg.equals("")) {rd = req.getRequestDispatcher("/login.jsp");req.setAttribute("err", errMsg);rd.forward(req, resp);}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doGet(req, resp);}}

DAO代码

package lee;import java.sql.*;/** * Description: * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a> * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee * <br/>This program is protected by copyright laws. * <br/>Program Name: * <br/>Date: * @author  Yeeku.H.Lee kongyeeku@163.com * @version  1.0 */public class DbDao{private Connection conn;private String driver;private String url;private String username;private String pass;public DbDao(){}public DbDao(String driver , String url, String username , String pass){this.driver = driver;this.url = url;this.username = username;this.pass = pass;}// 下面是各个成员属性的setter和getter方法public void setDriver(String driver) {this.driver = driver;}public void setUrl(String url) {this.url = url;}public void setUsername(String username) {this.username = username;}public void setPass(String pass) {this.pass = pass;}public String getDriver() {return (this.driver);}public String getUrl() {return (this.url);}public String getUsername() {return (this.username);}public String getPass() {return (this.pass);}// 获取数据库连接public Connection getConnection() throws Exception{if (conn == null){Class.forName(this.driver);conn = DriverManager.getConnection(url,username,this. pass);}return conn;}// 插入记录public boolean insert(String sql , Object... args)throws Exception{PreparedStatement pstmt = getConnection().prepareStatement(sql);for (int i = 0; i < args.length ; i++ ){pstmt.setObject( i + 1 , args[i]);}if (pstmt.executeUpdate() != 1){return false;}pstmt.close();return true;}// 执行查询public ResultSet query(String sql , Object... args)throws Exception{PreparedStatement pstmt = getConnection().prepareStatement(sql);for (int i = 0; i < args.length ; i++ ){pstmt.setObject( i + 1 , args[i]);}return pstmt.executeQuery();}// 执行修改public void modify(String sql , Object... args)throws Exception{PreparedStatement pstmt = getConnection().prepareStatement(sql);for (int i = 0; i < args.length ; i++ ){pstmt.setObject( i + 1 , args[i]);}pstmt.executeUpdate();pstmt.close();}// 关闭数据库连接的方法public void closeConn()throws Exception{if (conn != null && !conn.isClosed()){conn.close();}}}

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