一个处理用户登陆的servlet简单实例

本文实例讲述了一个处理用户登陆的servlet实现方法。分享给大家供大家参考。具体分析如下：

package com.bai;

import javax.servlet.http.*;

import java.io.*;

public class Login extends HttpServlet{
    public void doGet(HttpServletRequest req,HttpServletResponse res){
        try{req.setCharacterEncoding("gb2312");
        res.setContentType("text/html;charset=gb2312");
            PrintWriter pw=res.getWriter();
            pw.println("<html>");
            pw.println("<body>");
            pw.println("<h1>登陆界面</h1>");
            pw.println("<form action=logincl method=post>");
            pw.println("用户名:<input type=text name=username><br>");
            pw.println("密码:<input type=password name=passwd><br>");
            pw.println("<input type=submit value=login><br>");
            pw.println("</form>");
            pw.println("</body>");
            pw.println("</html>");
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }

    public void doPost(HttpServletRequest req,HttpServletResponse res){
        this.doGet(req,res);
    }
}

LoginCl.java代码如下：

复制代码代码如下:

package com.bai;

import javax.servlet.http.*;

import java.io.*;
import java.sql.*;

public class LoginCl extends HttpServlet{
    public void doGet(HttpServletRequest req,HttpServletResponse res){

        Connection conn=null;
        Statement stmt=null;
        ResultSet rs=null;
        String sql = "select username,passwd from users where username = ? and passwd = ?";
        try{//req.setCharacterEncoding("gb2312");
            String user=req.getParameter("username");
            String password=req.getParameter("passwd");

            Class.forName("com.mysql.jdbc.Driver");
            conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/sqdb","root","root");
//            stmt=conn.createStatement();
            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user);
            pstmt.setString(2, password);
            rs = pstmt.executeQuery();
//            rs=stmt.executeQuery("select top 1 * from users where username='"+user
//                +"' and passwd='"+password+"'");
            if(rs.next())
            {
                HttpSession hs=req.getSession(true);
                hs.setMaxInactiveInterval(60);
                hs.setAttribute("name",user);
                res.sendRedirect("welcome?&uname="+user+"&upass="+password);
            }
            else{
                res.sendRedirect("login"); //url
            }

        }
        catch(Exception e){
            e.printStackTrace();
        }finally{
            try{
                if(rs!=null){
                rs.close();
                }
                if(stmt!=null){
                    stmt.close();
                }
                if(conn!=null){
                    conn.close();
                }
            }catch(Exception e){
                e.printStackTrace();
            }
        }
    }

    public void doPost(HttpServletRequest req,HttpServletResponse res){
        this.doGet(req,res);
    }
}

其实上面这个处理用户名密码带有明显注入漏洞，可以根据用户名从数据库取密码，用取出的密码和用户输入的密码比较

复制代码代码如下:

sql=select passwd from users where username = ? limit 1

if(rs.next())
{
    String passwd=rs.getString(1);
    if(passwd.equals(password))
            //密码正确
    else //密码错误
}

Welcome.java代码如下：

复制代码代码如下:

package com.bai;

import javax.servlet.http.*;

import java.io.*;

public class Welcome extends HttpServlet{
    public void doGet(HttpServletRequest req,HttpServletResponse res){

        HttpSession hs=req.getSession();
        String val=(String)hs.getAttribute("pass");

        if(val==null){
            try{
                System.out.print(1);
                res.sendRedirect("login");
            }catch(Exception e){
                e.printStackTrace();
            }

        }

        String u=req.getParameter("uname");
        String p=req.getParameter("upass");

        try{//req.setCharacterEncoding("gb2312");
            PrintWriter pw=res.getWriter();
            pw.println("welcome! "+u+"&pass="+p);
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }

    public void doPost(HttpServletRequest req,HttpServletResponse res){
        this.doGet(req,res);
    }
}