內容：

1. 利用servlet生成驗證碼，
2. web.xml配置servlet
3. 在頁面中顯示生成的圖片，單擊重新整理

具體程式碼：

1. 利用servlet生成驗證碼

package com.wk.servlet;

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.web.xml配置servlet

<servlet>
    <description></description>
    <display-name>CheckImgServlet</display-name>
    <servlet-name>CheckImgServlet</servlet-name>
    <servlet-class>com.wk.servlet.CheckImgServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>CheckImgServlet</servlet-name>
    <url-pattern>/checkImg</url-pattern>
  </servlet-mapping>
 

3. 在頁面中顯示生成的圖片，單擊重新整理

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function checkImage(obj){
	obj.src="/Web/checkImg?time="+ new Date().getTime();
}

</script>
</head>
<body>
	<form action="/Web/login" method="post">
		使用者名稱：<input type="text" name="username"><br/>
		密碼：<input type="password" name="password"><br/>
		驗證碼<input type="text"> <img onclick="checkImage(this)" src="/Web/checkImg"><br/>
		<input type="submit" name="登入">

	</form>
</body>
</html>