效果如下：
IdentityServlet.java
package com.hxxy2003.firstproject;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
public class IdentityServlet extends HttpServlet {
public static final char[] CHARS={'2','3','4','5','6','7','8','9','A','B'
,'C','D','E','F','G','H','J','K','L','M','N','P','Q','R','S','T','U'
,'V','W','X','Y','Z'};
public static Random random=new Random();
public static String getRandomString(){
//字符串缓存
StringBuffer buffer=new StringBuffer();
for(int i=0;i<6;i++){
buffer.append(CHARS[random.nextInt(CHARS.length)]);
}
return buffer.toString();
}
public static Color getRandomColor(){
return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
}
public static Color getReverseColor(Color c){
return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());
}
/**
* Constructor of the object.
*/
public IdentityServlet() {
super();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("image/jpeg");
String randomString=getRandomString();//随机字符串
request.getSession(true).setAttribute("randomString", randomString);
int width=100;
int height=30;
Color color=getRandomColor();
Color reverse=getReverseColor(color);
BufferedImage bi=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g=bi.createGraphics();
g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16));
g.setColor(color);
g.fillRect(0, 0, width, height);
g.setColor(reverse);
g.drawString(randomString, 18, 20);
for(int i=0,n=random.nextInt(100);i<n;i++){
g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
}
ServletOutputStream out=response.getOutputStream();
JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);
encoder.encode(bi);
out.flush();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}
index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'index.jsp' starting page</title>
</head>
<script>
function reloadImage(){
document.getElementById('btn').disabled=true;
document.getElementById('identity').src='servlet/IdentityServlet?ts='
+new Date().getTime();
}
</script>
<body>
<img src="servlet/IdentityServlet" id="identity" onload="btn.disabled=false;" />
<input type="button" value="换个图片" onclick="reloadImage()" id="btn">
</body>
</html>