生成用户登录页面中验证码图片的Servlet

/*
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 * and open the template in the editor.
 */

package com.qixin.web;

import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 *
 * @author qixin
 */
public class ImageExample extends HttpServlet {
    //用于生成随机数
    private Random rand;
    //显示数字所用的字体
    private Font font;
    //图片的宽和高
    private int width;
    private int height;

    /**
     * 传入的参数为输出流。该方法生成图片并将数据写入输出流
     * @param out
     * @throws IOException
     */
    private void outputImage(OutputStream out) throws IOException{
        //生成1000-9999的随机数并转为字符串
        String str = Integer.toString(1000 + rand.nextInt(9000));
        //在内存中建立一个指定宽、高的图像
        BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //随机填入20个白色的像素点
        for (int i = 0; i < 20; i++) {
            int x = rand.nextInt(width);
            int y = rand.nextInt(height);
            bi.setRGB(x, y, 0xFFFFFF);
        }
        //获取该对象用于画字符图形
        Graphics g = bi.getGraphics();
        g.setFont(font);
        //画字符。注意后两个参数指定的是第一个字符的左下角坐标
        g.drawString(str, 0, height-1);
        //Graphics用完后立刻释放资源，避免等到垃圾回收时才进行。可减少资源占用率
        g.dispose();
        //将图像数据用jpg方式发送到输出流，该方法可能抛出IOException
        ImageIO.write(bi, "jpg", out);
    }

    @Override
    public void init(){
        rand = new Random(System.currentTimeMillis());
        font = new Font("Courier New",Font.ITALIC,20);
        width=50;
        height=20;
    }
    /** 
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        //设置MIME类型为jpeg图像
        response.setContentType("image/jpeg");
        //获取二进制输出流，并传给生成图像的方法以返回数据
        outputImage(response.getOutputStream());
    } 

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    } 

    /** 
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }

    /** 
     * Returns a short description of the servlet.
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}