jsp页面验证码(完整实例)

项目结构如下，MyEclipse中新建一个Web Project，取名servlet

1、src下new一个servlet类

package com.servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class IdentityServlet extends HttpServlet {

    public static final char[] chars={'','','','','','','','','A'};//自定义验证码池
    public static Random random=new Random();　　//随机数

    public static String getRandomString(){　　//获取6位随机数，放在图片里
        StringBuffer buffer=new StringBuffer();
        for(int i=;i<;i++){
            buffer.append(chars[random.nextInt(chars.length)]);
        }
        return buffer.toString();
    }

    public static Color getRandomColor(){　　//获取随机的颜色
        return new Color(random.nextInt(), random.nextInt(), random.nextInt());
    }

    public static Color getReverseColor(Color c){　　//返回某颜色的反色
        return new Color( - c.getRed(),  - c.getGreen(),  - c.getBlue());
    }

    /**
     * Constructor of the object.
     */
    public IdentityServlet() {
        super();
    }

    /**
     * Destruction of the servlet. <br>
     */
    public void destroy() {
        super.destroy(); // Just puts "destroy" string in log
        // Put your code here
    }

    /**
     * The doGet method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to get.
     *
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("image/jpeg");　　//设置输出类型

        String randomString = getRandomString();　　//随机字符串
        request.getSession(true).setAttribute("randomString", randomString);//放到session里

        int width=;　　//图片宽度
        int height=;　　//图片高度

        Color color=getRandomColor();　　//随机颜色，用于背景色
        Color reverse=getReverseColor(color);//反色，用于前景色
        //创建一个彩色图片
        BufferedImage bi=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g=bi.createGraphics();　　//绘图对象
        g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,));//设置字体
        g.setColor(color);//设置颜色
        g.fillRect(, , width, height);//绘制背景
        g.setColor(reverse);
        g.drawString(randomString, , );//绘制随机字符
        for(int i=,n=random.nextInt();i<n;i++){　　//画最多100个噪音点
            g.drawRect(random.nextInt(width), random.nextInt(height), , );
        }
        ServletOutputStream out= response.getOutputStream();//转成JPEG格式
        JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);//编码器
        encoder.encode(bi);　　//对图片进行编码
        out.flush();　　//输出到客户端
    }

    /**
     * The doPost method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to post.
     *
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doGet(request, response);
    }

    /**
     * Initialization of the servlet. <br>
     *
     * @throws ServletException if an error occurs
     */
    public void init() throws ServletException {
        // Put your code here
    }

}

2、web.xml，会自动生成servlet和servlet-mapping的配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name></display-name>
  <servlet>
    <servlet-name>IdentityServlet</servlet-name>
    <servlet-class>com.servlet.IdentityServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>IdentityServlet</servlet-name>
    <url-pattern>/servlet/IdentityServlet</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

3、WebRoot下新建一个html，展示验证码

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function reloadImage(){
    document.getElementById('btn').disabled=true;
    document.getElementById('identity').src='servlet/IdentityServlet?ts='+new Date().getTime();
}
</script>
</head>

<body>

<img src="servlet/IdentityServlet" id="identity" onload="btn.disabled=false;" />
<input type=button value="换个图片" onclick="reloadImage()" id="btn">
</body>
</html>

启动Tomcat，输入网址：http://localhost:8080/servlet/identity.html，效果如下：

点击‘换个图片’，会生成新的验证码