有两种方式，一种jsp方式，一种java方式（该方式自己改造的）

【采用jsp方式】
服务端生成代码：

java"><%@ page contentType="image/jpeg"
	import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"
	pageEncoding="gb2312"%>
<%
	response.setHeader("Pragma", "No-cache");
	response.setHeader("Cache-Control", "no-cache");
	response.setDateHeader("Expires", 0);

	try {
		//在内存中创建图象
		int width = 60; //图像的宽度
		int height = 20; //图像的高度
		BufferedImage image = new BufferedImage(width, height,
		BufferedImage.TYPE_INT_RGB);

		//获取图形上下文
		Graphics g = image.getGraphics();

		//设定背景色
		g.setColor(new Color(0xDCDCDC));
		g.fillRect(0, 0, width, height);

		//画边框
		g.setColor(Color.black);
		g.drawRect(0, 0, width - 1, height - 1);

		//取随机产生的认证码(4位数字)
		Random random = new Random();
		//生成0－9999的随机数
		int randomNum = random.nextInt(9999);
		//将验证码存在session中
		// session.setAttribute("rand",sRand);
		
		String randStr = String.valueOf(randomNum);

		switch (randStr.length()) {
		case 1:
			randStr = "000" + randStr;
			break;
		case 2:
			randStr = "00" + randStr;
			break;
		case 3:
			randStr = "0" + randStr;
			break;
		default:
			randStr = randStr.substring(0, 4);
			break;
		}
		request.getSession().setAttribute("rand",
				randStr);
		//将认证码显示到图象中
		g.setColor(Color.black);

		g.setFont(new Font("Atlantic Inline", Font.PLAIN, 18));
		String Str = randStr.substring(0, 1);
		g.drawString(Str, 8, 17);

		Str = randStr.substring(1, 2);
		g.drawString(Str, 20, 15);
		Str = randStr.substring(2, 3);
		g.drawString(Str, 35, 18);

		Str = randStr.substring(3, 4);
		g.drawString(Str, 45, 15);

		//          随机产生88个干扰点，使图象中的认证码不易被其它程序探测到
		for (int i = 0; i < 20; i++) {
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			g.drawOval(x, y, random.nextInt(5), random.nextInt(5));
		}

		//          图象生效
		g.dispose();

		//          输出图象到页面
		ImageIO.write(image, "JPEG", response.getOutputStream());
		out.clear();
		out = pageContext.pushBody();
	} catch (Exception e) {
		e.printStackTrace();
		out.println(e.toString());
	}
%>

客户端界面显示：

<script>
function show(o){
    var timenow = new Date().getTime();
    o.src="${base}/template2/common/image.jsp?d="+timenow;
}
</script>

<span>
<img src="${base}/template2/common/image.jsp" align="absmiddle" id="checkImage" 
onclick="show(document.getElementById('checkImage'))"/>
</span>
<a href="javascript>javascript:show(document.getElementById('checkImage'))"><span>看不清？换一张</span></a>

【采用java方式】
该方式有个弊端就是由于采用springmvc的responsebody注解无法有效设定response头清除缓存，所以多次调用同一个请求时候要在请求的url后面加随机数，如ur+”？data=“+new Date(),这样才能避免客户端不重复发同样请求到服务端的问题，搞IT的都懂这个方法，也知道什么原因，如有更好的解决办法请给予分享，谢谢

先创建一个Vcode类来作数据模型：

java">package com.wwwcoffee.base;

import java.awt.image.BufferedImage;

public class Vcode {
		private String code;
		private BufferedImage image;

		public String getCode() {
			return code;
		}

		public void setCode(String code) {
			this.code = code;
		}

		public BufferedImage getImage() {
			return image;
		}

		public void setImage(BufferedImage image) {
			this.image = image;
		}
	}

再创建一个辅助工具类生成校验码模型：

java">package com.wwwcoffee.utils;

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

import javax.imageio.ImageIO;

import com.wwwcoffee.base.Vcode;

public class VcodeUtil {

	public static Vcode generate() throws Exception {
		// 在内存中创建图象
		int width = 60; // 图像的宽度
		int height = 20; // 图像的高度
		BufferedImage image = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_RGB);

		// 获取图形上下文
		Graphics g = image.getGraphics();

		// 设定背景色
		g.setColor(new Color(0xDCDCDC));
		g.fillRect(0, 0, width, height);

		// 画边框
		g.setColor(Color.black);
		g.drawRect(0, 0, width - 1, height - 1);

		// 取随机产生的认证码(4位数字)
		Random random = new Random();
		// 生成0－9999的随机数
		int randomNum = random.nextInt(9999);
		String randStr = String.valueOf(randomNum);
		switch (randStr.length()) {
		case 1:
			randStr = "000" + randStr;
			break;
		case 2:
			randStr = "00" + randStr;
			break;
		case 3:
			randStr = "0" + randStr;
			break;
		default:
			randStr = randStr.substring(0, 4);
			break;
		}
		// 将认证码显示到图象中
		g.setColor(Color.black);
		g.setFont(new Font("Atlantic Inline", Font.PLAIN, 18));
		String Str = randStr.substring(0, 1);
		g.drawString(Str, 8, 17);

		Str = randStr.substring(1, 2);
		g.drawString(Str, 20, 15);
		Str = randStr.substring(2, 3);
		g.drawString(Str, 35, 18);

		Str = randStr.substring(3, 4);
		g.drawString(Str, 45, 15);

		// 随机产生88个干扰点，使图象中的认证码不易被其它程序探测到
		for (int i = 0; i < 20; i++) {
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			g.drawOval(x, y, random.nextInt(5), random.nextInt(5));
		}

		// 图象生效
		g.dispose();
		Vcode v = new Vcode();
		v.setCode(randStr);
		v.setImage(image);
		return v;
	}
}

最后在controller类的方法中调用实现：

java">/**
	 * 生成校验码
	 * @return
	 */
	@RequestMapping(value="getValidateCode")
	@ResponseBody
	public byte[] getValidateCode() {
		try {
			Vcode vcode = VcodeUtil.generate();
			//生成校验码放入session中
			this.getSession().setAttribute("vcodeserver", vcode.getCode());
			ByteArrayOutputStream baos = new ByteArrayOutputStream();
			ImageIO.write(vcode.getImage(), "JPEG", baos);
			return baos.toByteArray();
		} catch (Exception e) {
			log.error(e.getMessage(), e);
		}
		return null;
	}