1.驗證碼生成程式

將生成的圖片寫入response的輸出流中

 ImageIO.write(bufferedImage, "jpg", response.getOutputStream());

package com.hdh.content;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.BufferedReader;
import
 
 java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
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;

 
/**
 * 驗證碼生成程式
 * 
 * 
 * 
 */
public class CheckImgServlet extends HttpServlet {

    // 集合中儲存所有成語
    private List<String> words = new ArrayList<String>();

    @Override
    public void init() throws ServletException {
        // 初始化階段，讀取new_words.txt
        // web工程中讀取 檔案，必須使用絕對磁碟路徑
        String path = getServletContext().getRealPath("/WEB-INF/new_words.txt");
        
 
try {
            BufferedReader reader = new BufferedReader(new FileReader(path));
            String line;
            while ((line = reader.readLine()) != null) {
                words.add(line);
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 禁止快取
        // response.setHeader("Cache-Control", "no-cache");
        // response.setHeader("Pragma", "no-cache");
        // response.setDateHeader("Expires", -1);

        int width = 120;
        int height = 30;

        // 步驟一 繪製一張記憶體中圖片
        BufferedImage bufferedImage = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_RGB);

        // 步驟二 圖片繪製背景顏色 ---通過繪圖物件
        Graphics graphics = bufferedImage.getGraphics();// 得到畫圖物件 --- 畫筆
        // 繪製任何圖形之前 都必須指定一個顏色
        graphics.setColor(getRandColor(200, 250));
        graphics.fillRect(0, 0, width, height);

        // 步驟三 繪製邊框
        graphics.setColor(Color.WHITE);
        graphics.drawRect(0, 0, width - 1, height - 1);

        // 步驟四 四個隨機數字
        Graphics2D graphics2d = (Graphics2D) graphics;
        // 設定輸出字型
        graphics2d.setFont(new Font("宋體", Font.BOLD, 18));

        Random random = new Random();// 生成隨機數
        int index = random.nextInt(words.size());
        String word = words.get(index);// 獲得成語

        // 定義x座標
        int x = 10;
        for (int i = 0; i < word.length(); i++) {
            // 隨機顏色
            graphics2d.setColor(new Color(20 + random.nextInt(110), 20 + random
                    .nextInt(110), 20 + random.nextInt(110)));
            // 旋轉 -30 --- 30度
            int jiaodu = random.nextInt(60) - 30;
            // 換算弧度
            double theta = jiaodu * Math.PI / 180;

            // 獲得字母數字
            char c = word.charAt(i);

            // 將c 輸出到圖片
            graphics2d.rotate(theta, x, 20);
            graphics2d.drawString(String.valueOf(c), x, 20);
            graphics2d.rotate(-theta, x, 20);
            x += 30;
        }

        // 將驗證碼內容儲存session
        request.getSession().setAttribute("checkcode_session", word);

        // 步驟五 繪製干擾線
        graphics.setColor(getRandColor(160, 200));
        int x1;
        int x2;
        int y1;
        int y2;
        for (int i = 0; i < 30; i++) {
            x1 = random.nextInt(width);
            x2 = random.nextInt(12);
            y1 = random.nextInt(height);
            y2 = random.nextInt(12);
            graphics.drawLine(x1, y1, x1 + x2, x2 + y2);
        }

        // 將上面圖片輸出到瀏覽器 ImageIO
        graphics.dispose();// 釋放資源
        
        //將圖片寫到response.getOutputStream()中
        ImageIO.write(bufferedImage, "jpg", response.getOutputStream());

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

    /**
     * 取其某一範圍的color
     * 
     * @param fc
     *            int 範圍引數1
     * @param bc
     *            int 範圍引數2
     * @return Color
     */
    private Color getRandColor(int fc, int bc) {
        // 取其隨機顏色
        Random random = new Random();
        if (fc > 255) {
            fc = 255;
        }
        if (bc > 255) {
            bc = 255;
        }
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }

}

2.向一個<img/>標籤通過js中的time引數當單機驗證碼時不斷的重新整理地址

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
    function checkimg(obj) {
        obj.src="/WEB14/checkimg?time"+new Date().getTime();
    }
</script>
</head>
<body>
    <form action="/WEB13/login" method="post">
        使用者名稱：<input type="text" name="username"><br> 
        密碼：<input type="text" name="password"><br> 
        驗證碼：<input type="text"name="username"><img onclick="checkimg(this)"src="/WEB14/checkimg"> <br> 
        <input type="submit" value="登入"><br>
    </form>

</body>
</html>

3.執行結果