Java实现前台页面中的随机码

java后台代码：

package com.supermap.earth.rims.action;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;

import javax.imageio.ImageIO;
import javax.persistence.Entity;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;



/*****************************************************
 * 图形验证码Action
 * @author 
 * 
 * @since 2011-11-20
 *
 *****************************************************/
@Entity
public class PicCodeAction extends BaseAction {


	private static final long serialVersionUID = 1L;

	private static int width = 60;
	private static int height = 20;

	@Override
	public String execute() throws Exception {

		HttpSession session = this.getSession();
		HttpServletResponse response = this.getResponse();

		response.setContentType("image/jpeg");
		ServletOutputStream sos = response.getOutputStream();

		//设置浏览器不要缓存此图片   
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);

		//创建内存图象并获得其图形上下文   
		BufferedImage image = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();

		//产生随机的认证码   
		char[] rands = generateCheckCode();

		//产生图像   
		drawBackground(g);
		drawRands(g, rands);

		//结束图像的绘制过程，完成图像   
		g.dispose();

		//将图像输出到客户端   
		ByteArrayOutputStream bos = new ByteArrayOutputStream();
		ImageIO.write(image, "JPEG", bos);
		byte[] buf = bos.toByteArray();
		response.setContentLength(buf.length);
		//下面的语句也可写成：bos.writeTo(sos);  
		
		sos.write(buf);
		bos.close();
		sos.close();

		//将当前验证码存入到Session中   
		session.setAttribute("check_code", new String(rands));
		//直接使用下面的代码将有问题，Session对象必须在提交响应前获得   
		//request.getSession().setAttribute("check_code",new String(rands)); 
		return null;
	}

	private char[] generateCheckCode() {
		//定义验证码的字符表   
		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;
	}

	private void drawRands(Graphics g, char[] rands) {
		g.setColor(Color.BLACK);
		g.setFont(new Font(null, Font.ITALIC | Font.BOLD, 18));
		//在不同的高度上输出验证码的每个字符        
		g.drawString("" + rands[0], 1, 17);
		g.drawString("" + rands[1], 16, 15);
		g.drawString("" + rands[2], 31, 18);
		g.drawString("" + rands[3], 46, 16);
		
	}

	private void drawBackground(Graphics g) {
		//画背景   
		g.setColor(new Color(0xABDCEC));
		g.fillRect(0, 0, width, height);
		//随机产生120个干扰点   
		for (int i = 0; i < 10; 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);
		}
	}


}

xml配置：

<struts>
    <package name="piccode" extends="default" namespace="/piccode">
        <action name="piccode" method="execute" class="com.supermap.earth.rims.action.PicCodeAction">
        </action>
    </package>
</struts>

前台Jsp页面代码：

<p>
	<label for="piccode" style="font-size: 20">  验证码:</label>
	<input class="authenticode" type="text" name="piccode" id="piccode" maxlength="4" style="width: 105px;vertical-align: middle;" value="${piccode}" /><img src="${ctx}/piccode/piccode.do" id="code"  alt="点击刷新" style="cursor:hand;vertical-align: middle;" onclick="refreshcode();"/>
	<span style="" id="piccode_tip"></span>
</p>

和 js中的刷新function:

function refreshcode(){
			$('#code').attr('src','${ctx}/piccode/piccode.do?abc='+new Date());
		}