页面及时刷新验证码问题

index.jsp

 <img border="0" src="image.jsp" onclick="this.src='image.jsp'" title="看不清楚，点击图片即可刷新" style="cursor: hand;"> 

image.jsp 

<%@ page contentType="image/jpeg" import="java.io.*,java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %> <%! Random random = new Random(); Color getRandColor(int fc,int bc){//给定范围获得随机颜色 if(fc>255) fc=255; if(bc>255) bc=255; int r=fc+random.nextInt(bc-fc); int g=fc+random.nextInt(bc-fc); int b=fc+random.nextInt(bc-fc); return new Color(r,g,b); } String getVerifyCode() { String strBase = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"; int strBaseLen = strBase.length(); String verifyCode = ""; for (int i = 0; i < 6; i++) { int indexOf = random.nextInt(strBaseLen); verifyCode += strBase.substring(indexOf,indexOf+1); } return verifyCode; } %> <% String fontName[] = {"Arial", "Courier", "Courier New", "Times New Roman"}; int fontSizeMin = 30; int fontSizeMax = 30; int imageWidth = 150; int imageHeight = 35; int fontSize = 50; //设置页面不缓存 response.setHeader("Pragma","No-cache"); response.setHeader("Cache-Control","no-cache"); response.setDateHeader("Expires", 0); // 在内存中创建图象 BufferedImage gImage = new BufferedImage(imageWidth, imageHeight, BufferedImage.TYPE_INT_RGB); // 获取图形上下文 Graphics gGraphic = gImage.getGraphics(); //生成随机类 Random random = new Random(); // 设定背景色 gGraphic.setColor(getRandColor(200,250)); gGraphic.fillRect(0, 0, imageWidth, imageHeight); //画边框 gGraphic.setColor(new Color(random.nextInt(256),random.nextInt(256),random.nextInt(256))); gGraphic.drawRect(0,0,imageWidth-1,imageHeight-1); //产生300条以内的干扰线，使图象中的认证码不易被其它程序探测到 gGraphic.setColor(getRandColor(160,200)); int intLen = random.nextInt(300); for (int i=0;i <intLen;i++){ int x = random.nextInt(imageWidth); int y = random.nextInt(imageHeight); int xl = random.nextInt(imageWidth); int yl = random.nextInt(imageHeight); gGraphic.drawLine(x,y,x+xl,y+yl); } // 取随机产生的认证码(4位数字) String verifyCode = getVerifyCode(); int _style      = Font.BOLD; for (int i=0;i <verifyCode.length();i++){     String rand = verifyCode.substring(i,i+1);     fontSize = fontSizeMin+random.nextInt(fontSizeMax - fontSizeMin+1); //设定字体 gGraphic.setFont(new Font(fontName[random.nextInt(fontName.length)],Font.PLAIN,fontSize));     if (random.nextInt(100) > 40) _style ¦= Font.ITALIC;     // 将认证码显示到图象中     gGraphic.setColor(new Color(random.nextInt(256),random.nextInt(256),random.nextInt(256))); //调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成     gGraphic.drawString(rand,25*i+random.nextInt(4),(fontSize * 15 / 20)+4); } // 图象生效 gGraphic.dispose(); //将认证码存入session out.clear(); out = pageContext.pushBody(); session.setAttribute("veriryCode", verifyCode); //输出图象到页面 ImageIO.write(gImage, "JPEG", response.getOutputStream()); VerifyCodeTimer timerCode = new VerifyCodeTimer (request.getSession(),"veriryCode"); timerCode.timer.schedule(timerCode, 30 * 1000);//30秒钟 %> 

VerifyCodeTimer.java 文件

public class VerifyCodeTimer extends TimerTask {              private Timer timer; private HttpSession session; private String sessionKey; public VerifyCodeTimer(HttpSession session,String sessionKey) { timer = new Timer(); this.session = session; this.sessionKey = sessionKey; } public void run() { session.removeAttribute(sessionKey); //timer.cancel(); } } 

 

<img border="0" src="image.jsp" onclick="this.src='image.jsp'" title="看不清楚，点击图片即可刷新" style="cursor: hand;">

虽然你在验证码图片响应头中设置了

//设置页面不缓存response.setHeader("Pragma","No-cache");response.setHeader("Cache-Control","no-cache");response.setDateHeader("Expires", 0);

但这远远不够，如果你实际测试过就应该发现，有时点击验证码图片它并不会更新。原因在浏览器缓存。浏览器有时不会忠实的遵照你的响应头处理缓存。 改为如下：

<img src="image.jsp" title="看不清楚，点击图片即可刷新" style="border-style:none;cursor:hand;" onclick="this.src='image.jsp?temp='+(new Date().getTime().toString(36))">