servlet实现校验码

同事找的代码，关键是如下的这个CheckCodeServlet.java文件：

   
package com.megaeyes.web.util;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@SuppressWarnings("serial")
public class CheckCodeServlet extends HttpServlet{
    private static int WIDTH=56;
    private static int HEIGHT=18;
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException{
        HttpSession session = request.getSession();   
        response.setContentType("image/jpeg");
        ServletOutputStream sos = response.getOutputStream();
       
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setHeader("P3P", "CP=CAO PSA OUR");
       
        BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
        Graphics g=image.getGraphics();
       
        char[] rands = generateCheckCode();
        drawBackground(g);
        drawRands(g,rands);
        g.dispose();
       
        ByteArrayOutputStream bos= new ByteArrayOutputStream();
        ImageIO.write(image,"JPEG",bos);
        byte[] buf = bos.toByteArray();
        response.setContentLength(buf.length);
        sos.write(buf);
        bos.close();
        sos.close();
        session.setAttribute("check_code", new String(rands));
    }
   
    private void drawBackground(Graphics g){
        g.setColor(new Color(0xDCDCDC));
        g.fillRect(0, 0, WIDTH, HEIGHT);
        for(int i=0;i<120;i++){
            int x = (int)(Math.random()*WIDTH);
            int y = (int)(Math.random()*HEIGHT);
            int red = (int)(Math.random()*255);
            int green = (int)(Math.random()*255);
            int blue = (int)(Math.random()*255);
            g.setColor(new Color(red,green,blue));
            g.drawOval(x, y, 1, 0);
        }
    }

    private void drawRands(Graphics g, char[] rands) {
        g.setColor(Color.BLACK);
        g.setFont(new Font(null,Font.ITALIC|Font.BOLD,17));
        g.drawString(""+rands[0], 1, 15);
        g.drawString(""+rands[1], 16, 15);
        g.drawString(""+rands[2], 31, 18);
        g.drawString(""+rands[3], 45, 16);
    }

    private char[] generateCheckCode(){
        String chars = "0123456789";
        char[] rands = new char[4];
        for(int i=0;i<4;i++){
            int rand = (int)(Math.random()*10);
            rands[i]=chars.charAt(rand);
        }
        return rands;
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
}


在web.xml上要配置一下：
<servlet>
    <servlet-name>CheckCodeServlet</servlet-name>
    <servlet-class>com.megaeyes.web.util.CheckCodeServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>CheckCodeServlet</servlet-name>
    <url-pattern>/check</url-pattern>
</servlet-mapping>

页面上调用这个servlet:
<li id="yzm">验证码：<input name="" type="text" class="inputstyle2" />
<img id="validcode" src="check" onClick="refresh(this)" title="<fmt:message key='login.userCodeTip'/>" /></li>

src="check"就会去调用那个servlet了。另外点击refresh(this);的时候：
function refresh(obj){   
   obj.src="check";    
}

再调用一次servlet，重新生成一个图片

登录的时候，校验一下这个CODE
呵呵。从session中取：
if (!checkCode.equals((String) session.getAttribute("check_code"))