jsp过滤器（验证码）

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<filter>
<filter-name>TestFilter</filter-name>
<filter-class>filter.TestFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>TestFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>img</servlet-name>
<servlet-class>filter.TestImg</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>img</servlet-name>
<url-pattern>/imgCode</url-pattern>
</servlet-mapping>
</web-app>

package filter;

import java.io.*;
import java.util.*;
import com.sun.image.codec.jpeg.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;

/**
* Title: getImg.java Description: 这个class主要实现随机生成一个4位数的验证码，并写入session，
*/

public class TestImg extends HttpServlet {

private Font mFont = new Font("宋体", Font.PLAIN, 12);// 设置字体

// 处理post
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

doGet(request, response);
}

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 取得一个1000-9999的随机数
String s = "";
int intCount = 0;
intCount = (new Random()).nextInt(9999);//    
if (intCount < 1000)
intCount += 1000;
s = intCount + "";
// 对session付值。
HttpSession session = request.getSession(true);
session.setAttribute("getImg", s);
System.out.println(session.getAttribute("getImg"));
response.setContentType("image/gif");
ServletOutputStream out = response.getOutputStream();
BufferedImage image = new BufferedImage(35, 14,
BufferedImage.TYPE_INT_RGB);
Graphics gra = image.getGraphics();
// 设置背景色
gra.setColor(Color.yellow);
gra.fillRect(1, 1, 33, 12);
// 设置字体色
gra.setColor(Color.black);
gra.setFont(mFont);
// 输出数字
char c;
for (int i = 0; i < 4; i++) {
c = s.charAt(i);
gra.drawString(c + "", i * 7 + 4, 11); // 7为宽度，11为上下高度位置
}
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
encoder.encode(image);
out.close();
}
}


package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class TestFilter implements Filter{

public void destroy() {

}

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest)request;
HttpServletResponse rep = (HttpServletResponse)response;
System.out.println(req.getRequestURI());

rep.setHeader("Pragma","No-cache");
rep.setHeader("Cache-Control","no-cache");
rep.setDateHeader("Expires", 0);
chain.doFilter(req, rep);
}

public void init(FilterConfig arg0) throws ServletException {

}
}