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={'2','3','4','5','6','7','8','9','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=0;i<6;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(255), random.nextInt(255), random.nextInt(255));}public static Color getReverseColor(Color c){　　//返回某颜色的反色return new Color(255 - c.getRed(), 255 - c.getGreen(), 255 - 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=100;　　//图片宽度int height=30;　　//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,16));//设置字体g.setColor(color);//设置颜色g.fillRect(0, 0, width, height);//绘制背景g.setColor(reverse);g.drawString(randomString, 18, 20);//绘制随机字符for(int i=0,n=random.nextInt(100);i<n;i++){　　//画最多100个噪音点g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);}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" οnlοad="btn.disabled=false;" />
<input type=button value="换个图片" οnclick="reloadImage()" id="btn">
</body>
</html>