做了一個小例子，web在登陸的時候一般都有驗證碼驗證，這裏用servlet來製作一個驗證碼。
servlet：
package com.zhkunion.util;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
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;
/**
* 生成圖片驗證碼的servlet
* @author maojycom
* 創建日期: 2014-11-6 上午11:44:02
* @version 1.0.0
*/
public class CheckCode extends HttpServlet{
private static final long serialVersionUID = 2011594857610014291L;
private static final int WIDTH = 80;
private static final int HEIGHT = 26;
private final String BASES = "123456789ABCDEFGEFGHJKLMNPQapcdefghlkjmnpgwq";
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
//聲明返回的MIME類型
response.setContentType("image/jpeg");
BufferedImage image = new BufferedImage(WIDTH, HEIGHT, 1);
Graphics g = image.getGraphics();
setBackground(g);
setBorder(g);
String num = drawRandomNum((Graphics2D)g);
//把驗證碼存放到session中去
request.getSession().setAttribute("checkCode", num);
drawRandomLine(g);
//以圖像流方式輸出圖片
ImageIO.write(image, "jpg", response.getOutputStream());
}
/**
* 隨機生成數字
* @param g
* @return
*/
public String drawRandomNum(Graphics2D g) {
g.setColor(Color.red);
g.setFont(new Font("宋體", 1, 20));
StringBuffer sb = new StringBuffer();
int x = 5;
for (int i = 0; i < 4; i++){
String ch = BASES.charAt(new Random().nextInt(BASES.length())) + "";
sb.append(ch);
g.drawString(ch, x, 20);
x += 20;
}
return sb.toString();
}
/**
* 隨機畫干擾線
* @param g
*/
private void drawRandomLine(Graphics g) {
g.setColor(Color.GRAY);
for (int i = 0; i < 10; i++) {
int x1 = new Random().nextInt(80);
int y1 = new Random().nextInt(26);
int x2 = new Random().nextInt(80);
int y2 = new Random().nextInt(26);
g.drawLine(x1, y1, x2, y2);
}
}
/**
* 設置邊框
* @param g
*/
public void setBorder(Graphics g){
g.setColor(Color.BLUE);
g.drawRect(1, 1, 78, 24);
}
/**
* 設置背景
* @param g
*/
public void setBackground(Graphics g) {
g.setColor(Color.WHITE);
g.fillRect(0, 0, 80, 80);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
doGet(request, response);
}
}
在web.xml中配置該servlet驗證碼：
<!-- 配置驗證碼的路徑 -->
<servlet>
<servlet-name>checkCode</servlet-name>
<servlet-class>net.seehope.util.CheckCode</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>checkCode</servlet-name>
<url-pattern>/checkCode.jpg</url-pattern>
</servlet-mapping>在頁面中使用：
<script type="text/javascript">
//實現當點擊圖片是能切換
function change(img){
img.src = img.src + "?" + new Date().getTime();
}
</script>
</head>
<body>
驗證碼：<img alt="驗證碼" src="checkCode.jpg" onclick="change(this)">
</body>補充：有時從服務器端生成的驗證碼跟從JSP頁面填寫的驗證碼不一致，因爲服務器端生成的驗證碼是存放到session中的，
而加載JSP比加載session要快，這導致了JSP中顯示的驗證碼是剛生成的，但session中的驗證碼還是上一次的，還沒有清除、更新。
1，及時清除session中的驗證碼，確保能讀到最新的驗證碼；
2，有JSP生成驗證碼，再傳給後臺，讓後臺在驗證碼上畫干擾線及顏色背景等。