JavaWeb用户登录功能的实现大四快毕业了，3年多的时间中，乱七八糟得学了一大堆，想趁找工作之前把所学的东西整理一遍，所以就尝试着做一个完整的JavaWeb系统，这几天试着做了一个用户登录的功能，分享给大家，肯定有很多不完善的地方，希望大家提提宝贵的意见，必将努力完善它。
我贴出此篇博客的目的是，将一些以后有可能用到的重复性的代码保存下来，用于以后需要时直接复制粘贴，所以，此篇博客大部分都是代码，讲解性的语句并不多，如果大家看得头疼，不如不看，以后万一用到的话再拿过来修修改改即可。
有可能用得到的部分：生成验证码的Java类、操作数据库的Java类用户登录模块采用了多种语言：Html、css、query：页面Servlet、java：后台运行效果图：Login.html代码：<!DOCTYPE html><html><head lang="en"><meta charset="UTF-8"><title>登录界面</title><script src="js/jquery-1.11.1.js"></script><script src="js/login.js"></script><link href="css/style.css" rel="stylesheet" type="text/css" /></head><body><div id="loginpanelwrap"><div class="loginheader"><div class="logintitle">登录</div></div><form action = "/UserLogin/Sample1/loginServlet"><div class="loginform"><div class="loginform_row"><label>用户名:</label><input type="text" class="loginform_input" name="username" /></div><div class="loginform_row"><label>密码:</label><input type="password" class="loginform_input" name="password" /> </div><div class = "loginform_row"><label>验证码:</label><input type = "text" class="loginform_input_validationCode" name = "validationCode"/><img class = "validationCode_img" src="/UserLogin/Sample1/validationCode"></div><div class="loginform_row"><span class = "returnInfo"></span><input type="submit" class="loginform_submit" value="登录" /></div><div class="clear"></div></div></form></div></body></html>JQuery代码：login.js$(function(){$(".loginform_submit").click(function(){if(checkInput()) {$("form").action("/loginServlet");}else{return false;}});$(".validationCode_img").click(function(){$(".validationCode_img").attr("src","/UserLogin/Sample1/validationCode?"+Math.random());});function checkInput(){//判断用户名if($("input[name=username]").val() == null || $("input[name=username]").val() == ""){ alert("用户名不能为空");$("input[name=username]").focus();return false;}//判断密码if($("input[name=password]").val() == null || $("input[name=password]").val() == ""){ alert("密码不能为空");$("input[name=password]").focus();return false;}//判断验证码if($("input[name=validationCode]").val() == null || $("input[name=validationCode]").val() == ""){alert("验证码不能为空");$("input[name=validationCode]").focus();return false;}return true;}});生成验证码的Servlet：ValidationCode.javapackage erlogin.sample;import javax.imageio.ImageIO;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import java.awt.*;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.OutputStream;import java.util.Random;/*** Created by zhang on 2014/9/13.*/public class ValidationCode extends HttpServlet{@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获得验证码集合的长度int charsLength = codeChars.length();//下面3条记录是关闭客户端浏览器的缓冲区//这3条语句都可以关闭浏览器的缓冲区，但是由于浏览器的版本不同，对这3条语句的支持也不同//因此，为了保险起见，同时使用这3条语句来关闭浏览器的缓冲区resp.setHeader("ragma", "No-cache");resp.setHeader("Cache-Control", "no-cache");resp.setDateHeader("Expires", 0);//设置图形验证码的长和宽int width = 90, height = 30;BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);Graphics g = image.getGraphics(); //获得用于输出文字的Graphics对象Random random = new Random();g.setColor(getRandomColor(180, 250));g.fillRect(0, 0, width, height);g.setFont(new Font("Times New Roman",Font.ITALIC,height));g.setColor(getRandomColor(120, 180));//用户保存最后随机生成的验证码StringBuilder validationCode = new StringBuilder();//验证码的随机字体String[] fontNames = {"Times New Roman","Book antiqua","Arial"};//随机生成3-5个验证码for(int i = 0; i < 4; i++){//随机设置当前验证码的字符的字体g.setFont(new Font(fontNames[random.nextInt(3)],Font.ITALIC,height));//随机获得当前验证码的字符char codeChar = codeChars.charAt(random.nextInt(charsLength));validationCode.append(codeChar);//随机设置当前验证码字符的颜色g.setColor(getRandomColor(10, 100));//在图形上输出验证码字符，x和y都是随机生成的g.drawString(String.valueOf(codeChar), 16*i + random.nextInt(7), height-random.nextInt(6));}//获得HttpSession对象HttpSession session = req.getSession();//设置session对象5分钟失效session.setMaxInactiveInterval(5*60);//将验证码保存在session对象中,key为validation_codesession.setAttribute("validation_code", validationCode.toString());//关闭Graphics对象g.dispose();OutputStream outS = resp.getOutputStream();ImageIO.write(image, "JPEG", outS);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req,resp);}//图形验证码的字符集，系统将随机从这个字符串中选择一些字符作为验证码private static String codeChars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";//返回一个随机颜色private static Color getRandomColor(int minColor, int maxColor){Random random = new Random();if(minColor > 255){minColor = 255;}if(maxColor > 255){maxColor = 255;}//获得r的随机颜色值int red = minColor + random.nextInt(maxColor-minColor);//gint green = minColor + random.nextInt(maxColor-minColor);//bint blue = minColor + random.nextInt(maxColor-minColor);return new Color(red,green,blue);}}操作数据库的代码:ManageSQLServer2008.java(本人使用的数据库为SQLServer 2008)package erlogin.sample.dbmanager;import java.beans.Statement;import java.sql.*;public class ManageSQLServer2008 {//数据库的驱动名private final String dbDriver = "com.microsoft.sqlserver.jdbc.SQLServerDriver";//数据库的url地址private final String url = "jdbc:sqlserver://localhost:1433;databaseName=zhDemo";private final String userName = "sa";private final String password = "123";private Connection conn = null;public ManageSQLServer2008(){//加载数据库驱动try {Class.forName(dbDriver).newInstance();//System.out.println("加载驱动成功");} catch (Exception e) {e.printStackTrace();System.err.println("数据库驱动加载失败");}//获取数据库链接try {conn = DriverManager.getConnection(url,userName,password);} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();System.err.println("获取数据库链接失败");}}//执行各种SQL语句的方法private ResultSet execSQL(String sql,Object... args) throws SQLException{//建立PreparedStatement对象PreparedStatement pStmt = conn.prepareStatement(sql);//为pStmt对象设置SQL参数值for(int i = 0; i < args.length; i++){pStmt.setObject(i+1, args[i]);}//执行SQL语句pStmt.execute();//返回结果集,如果执行的SQL语句不返回结果集，则返回nullreturn pStmt.getResultSet();}private void closeSQLConn(){//关闭数据库链接if(conn != null){try {conn.close();} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}public String checkUser(String username,String password){boolean has_username = false;boolean password_correct = false;ResultSet rs = null;try {rs = execSQL("select * from zh_users");} catch (SQLException e) {System.err.println("查询数据库出错");e.printStackTrace();return null;}try {while(rs.next()){String temp_username = rs.getString("user_name").trim();String temp_password = rs.getString("password_md5").trim();if(username.equals(temp_username)){has_username = true;if(password.equals(temp_password)){password_correct = true;return "hasUserNameAndPasswordCorrect";}return "hasUserNameButPasswordInCorrect";}}} catch (SQLException e) {System.err.println("操作ResultSet出错");e.printStackTrace();}return "hasNoUserName";}}用于处理用户登录的Servlet:LoginServlet.javapackage erlogin.sample;import erlogin.sample.dbmanager.ManageSQLServer2008;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;import java.io.IOException;import java.io.OutputStream;/*** Created by zhang on 2014/9/13.*/public class LoginServlet extends HttpServlet{@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {OutputStream out = resp.getOutputStream();String username = req.getParameter("username");String password = req.getParameter("password");String validationCode = req.getParameter("validationCode");HttpSession session = req.getSession();String validation_code = (String)session.getAttribute("validation_code");if(validationCode.equalsIgnoreCase(validation_code)){System.out.println("验证码正确");}else{System.out.println("验证码错误");}ManageSQLServer2008 mss = new ManageSQLServer2008();String result = mss.checkUser(username,password);if (result.equals("hasUserNameAndPasswordCorrect")) {System.out.println("用户名和密码均正确");} else if (result.equals("hasUserNameButPasswordInCorrect")) {System.out.println("用户名正确,密码不正确");} else if (result.equals("hasNoUserName")) {System.out.println("没有此用户");}//转发到result.jspRequestDispatcher rd = req.getRequestDispatcher("Login.html");rd.forward(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req,resp);}}web.xml文件的配置:<servlet><servlet-name>loginServlet</servlet-name><servlet-class>erlogin.sample.LoginServlet</servlet-class></servlet><servlet-mapping><servlet-name>loginServlet</servlet-name><url-pattern>/loginServlet</url-pattern></servlet-mapping><servlet><servlet-name>validationCode</servlet-name><servlet-class>erlogin.sample.ValidationCode</servlet-class></servlet><servlet-mapping><servlet-name>validationCode</servlet-name><url-pattern>/validationCode</url-pattern></servlet-mapping>最后的style.css代码，太多了，而且有点乱，所以就没有贴出来，至于CSS代码，大家可以去网上下载：/tag_moban/htmlMoBan.html这个上面就有好多，大家根据喜好选择一个，然后稍加即可。