servlet登陆界面，连接数据库

package com.servlet; import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; 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; public class LoginServlet extends HttpServlet{ Connection conn; public void destroy(){ super.destroy(); } public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException{ doPost(request,response); } public void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException{ response.setContentType("text/html"); request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); String username=request.getParameter("username"); String password=request.getParameter("password"); if(conn!=null){ String sql="select * from user where username=? and password=?"; try{ PreparedStatement ps=conn.prepareStatement(sql); ps.setString(1,username); ps.setString(2,password); request.setAttribute("username",username); //将用户名和密码存入request request.setAttribute("password",password); ResultSet rs=ps.executeQuery(); if(rs.next()){ //PrintWriter out=response.getWriter(); //out.println("....数据库连接成功！"+username+"--存在于数据库"); //验证码判断 HttpSession session = request.getSession(); String rand=(String)session.getAttribute("rand"); String input=request.getParameter("rand"); //out.println("系统验证码为："+rand); //out.println(""); //out.println("您输入的验证码为："+input); //out.println(""); //out.flush(); //out.close(); if(rand.equals(input)){ /*out=response.getWriter(); out.println("hello,验证成功！"); out.flush(); out.close();*/ //request.getRequestDispatcher("/SucServlet").forward(request, response); RequestDispatcher dispatcher=request.getRequestDispatcher("/success.jsp"); try{ dispatcher.forward(request, response); return; }catch(Exception e){} }else{ /*PrintWriter out=response.getWriter(); out.println("hello,验证失败！"); out.flush(); out.close();*/ RequestDispatcher dispatcher=request.getRequestDispatcher("/fail.jsp"); try{ dispatcher.forward(request, response); return; }catch(Exception e){} } }else{ /*PrintWriter out=response.getWriter(); out.println("数据库连接失败！"+username+"--查无此人，请重新登录！"); out.flush(); out.close(); //跳转页面*/ RequestDispatcher dispatcher=request.getRequestDispatcher("/fail.jsp"); try{ dispatcher.forward(request, response); return; }catch(Exception e){} } }catch(SQLException e){ e.printStackTrace(); } } } public void init()throws ServletException{ super.init(); try{ Class.forName("com.mysql.jdbc.Driver"); String url="jdbc:mysql://localhost:3306/LoginDemo"; conn=DriverManager.getConnection(url,"root","123456"); System.out.println("数据库连接成功！"); }catch(Exception e){ e.printStackTrace(); System.out.println("数据库连接失败！"); } } }