在jsp页面里怎么样刷新用Servlet产生的验证码?
<input type="text" name="Rand" maxlength="4" size="4" /> <img border="0" src="validatecodeservlet" alt=""/>
请高手赐教
<input type="text" name="Rand" maxlength="4" size="4" /> <img border="0" src="validatecodeservlet" alt=""/>
请高手赐教
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import com.sun.image.codec.jpeg.*;
import java.awt.*;
import com.sun.image.codec.jpeg.*;
import java.awt.image.BufferedImage;
import java.awt.image.DataBuffer;
import java.awt.geom.GeneralPath;
import javax.swing.*;
import java.math.*;
public class Servlet1
extends HttpServlet {
//Process the HTTP Get request
public void doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {
response.setContentType(request.getContentType());
response.setContentType("image/jpeg"); //必须设置ContentType为image/jpeg
int length = 4; //设置默认生成4个数字
Date d = new Date();
long lseed = d.getTime();
java.util.Random r = new Random(lseed); //设置随机种子
if (request.getParameter("length") != null) {
try {
length = Integer.parseInt(request.getParameter("length"));
}
catch (NumberFormatException e) {
}
}
StringBuffer str = new StringBuffer();
for (int i = 0; i < length; i++) {
str.append(r.nextInt(9)); //生成随机数字
}
//可以在此加入保存验证码的代码
//创建内存图像
BufferedImage bi = new BufferedImage(40, 16, BufferedImage.TYPE_INT_RGB);
Graphics2D g = bi.createGraphics();
g.clearRect(0, 0, 16, 40);
g.setColor(Color.RED);
g.drawString(str.toString(), 4, 12);
try {
//使用JPEG编码,输出到response的输出流
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.
getOutputStream());
JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(bi);
param.setQuality(1.0f, false);
encoder.setJPEGEncodeParam(param);
encoder.encode(bi);
}
catch (Exception ex) {
}
}
}然后在需求显示验证码的加入以下代码就可以了<img alt="" src="/WebModule1/servlet1" width="40" height="16"/>
刷新页面即可
欢迎大家一起来切磋交流..
共同进步..
但是由于缓存的问题,如果两次都是同样的值,浏览器一般都不会刷新,所以需要给图片连接每次做一点没有影响改动如:
<img alt="看不清楚?点击更换验证码" src="/WebModule1/servlet1" width="40" height="16" onclick="this.src='/WebModule1/servlet1'+Math.random()+100"/>
onclick="this.src='/WebModule1/servlet1?a='+Math.random()+100"
<a href="javascript:changeCode();">看不清</a><script>
function changeCode()
{
document.getElementById("cc").src="checkcode";
}
</script>