验证码的实现

如何实现一个服务器一个session为一个用户服务的/

为什么要验证码？

原理（java的绘图技术）

验证码：

package com.dalao;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class CodeUtil
 */
@WebServlet("/codeutil")
public class CodeUtil extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public CodeUtil() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // System.out.println("哈哈哈");
        response.setContentType("image/jpeg");
        // 设置页面不缓存
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        // 在内存中创建图像
        int width = 90;
        int height = 35;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        // 获取图形上下文
        Graphics g = image.getGraphics();
        // 随机类
        Random random = new Random();
        // 设定背景
        g.setColor(getRandColor(200, 250));
        g.fillRect(0, 0, width, height);
        // 设定字体
        g.setFont(new Font("Times New Roman", Font.PLAIN, 30));
        // 随机产生干扰线
        g.setColor(getRandColor(160, 200));
        for (int i = 0; i < 100; i++) {
            int x = random.nextInt(width);
            int y = random.nextInt(height);
            int xl = random.nextInt(12);
            int yl = random.nextInt(12);
            g.drawLine(x, y, x + xl, y + yl);
        }
        // 随机产生4位验证码
        String[] codes = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H",
                "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "a", "b", "c",
                "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x",
                "y", "z" };
        String code = "";
        for (int i = 0; i < 4; i++) {
            String str = codes[random.nextInt(codes.length)];
            code += str;
            // 将认证码显示到图象中
            g.setColor(new Color(50 + random.nextInt(110), 20 + random.nextInt(110), 30 + random.nextInt(110)));
            // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
            g.drawString(str, 18 * i + 13, 27); // 文字间距*i+距离左边距，上边距
        }
        HttpSession session = request.getSession();
        // 将认证码存入SESSION
        session.setAttribute("code", code);
        // 图象生效
        g.dispose();
        // 输出图象到页面
        ImageIO.write(image, "JPEG", response.getOutputStream());
        // 加上下面代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has
        // already been called ..........等异常
        response.getOutputStream().flush();
        response.getOutputStream().close();
        response.flushBuffer();
    }

    // 获取随机颜色
    private Color getRandColor(int fc, int bc) {
        Random random = new Random();
        if (fc > 255)
            fc = 255;
        if (bc > 255)
            bc = 255;
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}

登录界面;

package com.dalao;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Loin
 */
@WebServlet("/Loin")
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
        //浏览器uft-8展示
        response.setContentType("text/html;charset=utf-8");
        request.setCharacterEncoding("utf-8");
        PrintWriter out=response.getWriter();
        //返回一个界面
//        out.println("你好");
        out.print("<img src='img/1.gif'/><hr/>");
        out.println("<h1>用户登录</h1>");
        out.println("<form action='/mycheckCode/LoinCL' method='post'>");
        out.println("用户id:<input type='text' name='id'></br>");
        out.println("密 码:<input type='password' name='password'></br>");
        out.println("验证码:<input type='text' name='checkcode'><img src='/mycheckCode/codeutil'></br>");
        out.println("<input type='submit' value='登录'></br>");
        out.println("</form>");
        String err=(String) request.getAttribute("err");
        if(err!=null){
            out.print(err);
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.doGet(request,response);
    }

}

登录界面的控制;

package com.dalao;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoinCL
 */
@WebServlet("/LoinCL")
public class LoinCL extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoinCL() {
        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.setContentType("text/html;charset=utf-8");
        request.setCharacterEncoding("utf-8");
        PrintWriter out=response.getWriter();
        //获取用户的ID password 输入的验证码
        //1.先验证码
        String id=request.getParameter("id");
        String password=request.getParameter("password");
        String checkcode=request.getParameter("checkcode");
        //取出session中验证码
        String checkcode2=(String) request.getSession().getAttribute("code");
        if(checkcode.equals(checkcode2)){
            out.print("验证码正确");
        }else{
//            out.print("重新输入");
            request.setAttribute("err", "验证码错误");
            request.getRequestDispatcher("/Loin").forward(request, response);

            
        }
        
        
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.doGet(request, response);
    }

}