package com.servlet;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'};//自定義驗證碼池  public static Random random=new Random();　　//隨機數    public static String getRandomString(){　　//獲取6位隨機數，放在圖片里    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(){　　//獲取隨機的顏色    return new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255));  }    public static Color getReverseColor(Color c){　　//返回某顏色的反色    return new Color(255 - c.getRed(), 255 - c.getGreen(), 255 - c.getBlue());  }    /**   * Constructor of the object.   */  public IdentityServlet() {    super();  }  /**   * Destruction of the servlet. <br>   */  public void destroy() {    super.destroy(); // Just puts "destroy" string in log    // Put your code here  }  /**   * The doGet method of the servlet. <br>   *   * This method is called when a form has its tag value method equals to get.   *    * @param request the request send by the client to the server   * @param response the response send by the server to the client   * @throws ServletException if an error occurred   * @throws IOException if an error occurred   */  public void doGet(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {    response.setContentType("image/jpeg");　　//設置輸出類型        String randomString = getRandomString();　　//隨機字符串    request.getSession(true).setAttribute("randomString", randomString);//放到session里        int width=100;　　//圖片寬度    int height=30;　　//圖片高度        Color color=getRandomColor();　　//隨機顏色，用于背景色    Color reverse=getReverseColor(color);//反色，用于前景色    //創建一個彩色圖片    BufferedImage bi=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    Graphics2D g=bi.createGraphics();　　//繪圖對象    g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16));//設置字體    g.setColor(color);//設置顏色    g.fillRect(0, 0, width, height);//繪制背景    g.setColor(reverse);    g.drawString(randomString, 18, 20);//繪制隨機字符    for(int i=0,n=random.nextInt(100);i<n;i++){　　//畫最多100個噪音點      g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);    }    ServletOutputStream out= response.getOutputStream();//轉成JPEG格式    JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);//編碼器    encoder.encode(bi);　　//對圖片進行編碼    out.flush();　　//輸出到客戶端  }  /**   * The doPost method of the servlet. <br>   *   * This method is called when a form has its tag value method equals to post.   *    * @param request the request send by the client to the server   * @param response the response send by the server to the client   * @throws ServletException if an error occurred   * @throws IOException if an error occurred   */  public void doPost(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {    doGet(request, response);  }  /**   * Initialization of the servlet. <br>   *   * @throws ServletException if an error occurs   */  public void init() throws ServletException {    // Put your code here  }}

<?xml version="1.0" encoding="UTF-8"?><web-app version="3.0"   xmlns="http://java.sun.com/xml/ns/javaee"   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> <display-name></display-name> <servlet>  <servlet-name>IdentityServlet</servlet-name>  <servlet-class>com.servlet.IdentityServlet</servlet-class> </servlet> <servlet-mapping>  <servlet-name>IdentityServlet</servlet-name>  <url-pattern>/servlet/IdentityServlet</url-pattern> </servlet-mapping>   <welcome-file-list>  <welcome-file>index.jsp</welcome-file> </welcome-file-list></web-app>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title><script type="text/javascript">function reloadImage(){  document.getElementById('btn').disabled=true;  document.getElementById('identity').src='servlet/IdentityServlet?ts='+new Date().getTime();}</script></head><body><img src="servlet/IdentityServlet" id="identity" onload="btn.disabled=false;" /><input type=button value="換個圖片" onclick="reloadImage()" id="btn"></body></html>