javaweb登录功能实现，eclipse开发工具，mysql作为数据库

package com.test; import java.io.IOException; import java.io.PrintWriter; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.mysql.jdbc.Connection; /** * Servlet implementation class LoginServlet */ //如果在web.xml中声明过servlet 就把这一句注释掉 //@WebServlet("/LoginServlet") public class LoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public LoginServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getWriter().append("Served at: ").append(request.getContextPath()); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("utf-8"); response.setCharacterEncoding("utf-8"); response.setContentType("text/html; charset=UTF-8"); //mysql数据库驱动 String driver = "com.mysql.jdbc.Driver"; //链接数据库的url test为数据库名 String url = "jdbc:mysql://127.0.0.1:3306/test"; //数据库用户 String user = "root"; //数据库密码 String password = "yanglong123"; //从前台读取到的用户名 String username = request.getParameter("username"); //从前台读取到的密码 String pwd = request.getParameter("pwd"); //数据库链接成功时返回的实例 Connection conn = null; //查询成功时返回的记录集 ResultSet rs = null; try{ //加载驱动 Class.forName(driver); //获取链接 conn = (Connection) DriverManager.getConnection(url, user, password); //准备sql查询 String sql = "select * from User where username=? and pwd=?"; //使用PreparedStatement，可以防止sql注入 PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, username); ps.setString(2, pwd); //执行查询,返回记录集 rs = ps.executeQuery(); //如果查询到用户名和密码，则允许用户登录 if (rs.next()){ System.out.println("login ok!!"); PrintWriter out = response.getWriter(); out.flush(); out.println("<script>"); out.println("alert('恭喜，登录成功');"); out.println("history.back();"); out.println("</script>"); out.close(); }else{ System.out.println("login fail!!"); PrintWriter out = response.getWriter(); out.flush(); out.println("<script>"); out.println("alert('很遗憾，用户名或密码错误');"); out.println("history.back();"); out.println("</script>"); out.close(); } //关闭PreparedStatement ps.close(); }catch(Exception e){ e.printStackTrace(); }finally{ //最后一定要关闭链接 if (conn != null){ try { conn.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } if(rs != null){ try { rs.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } doGet(request, response); } }