java实现验证码登录

java实现验证码的步骤：

1.创建验证码的实体类，代码如下：

1. import java.awt.BasicStroke;
2. import java.awt.Color;
3. import java.awt.Font;
4. import java.awt.Graphics2D;
5. import java.awt.image.BufferedImage;
6. import java.io.IOException;
7. import java.io.OutputStream;
8. import java.util.Random;
9. import javax.imageio.ImageIO;
10. public class VerifyCode {
11. /**
12. *楠岃瘉鐮?
13. * @author 瑕冧匠鍗?
14. */
15. private int w = 50;
16. private int h = 25;
17. private Random r = new Random();
18. private String[] fontNames = {"瀹嬩綋","鍗庢枃妤蜂綋","榛戜綋","寰蒋闆呴粦","妤蜂綋_GB2312"};
19. private String codes = "23456789abcdefghjkmnpqrstuvwxyzABCEFGHIJKLMNPQRSTUVWXYZ";
20. private Color bgColor = new Color(255,255,255);
21. private String text;
22. private Color randomColor(){
23. int red = r.nextInt(200);
24. int green = r.nextInt(200);
25. int blue = r.nextInt(200);
26. return new Color(red,green,blue);
27. }
28. private Font randomFont(){
29. int index = r.nextInt(fontNames.length);
30. String fontName = fontNames[index];
31. int style = r.nextInt(4);
32. int size = r.nextInt(6)+15;
33. return new Font(fontName,style,size);
34. }
35. private void drawLine(BufferedImage image){
36. int num = 3;
37. Graphics2D g2 = (Graphics2D)image.getGraphics();
38. for(int i=0;i<num;i++){
39. int x1 = r.nextInt();
40. int y1 = r.nextInt();
41. int x2 = r.nextInt();
42. int y2 = r.nextInt();
43. g2.setStroke(new BasicStroke(1.5F));
44. g2.setColor(Color.BLUE);
45. g2.drawLine(x1,y1,x2,y2);
46. }
47. }
48. private char randomChar(){
49. int index = r.nextInt(codes.length());
50. return codes.charAt(index);
51. }
52. private BufferedImage createImage(){
53. BufferedImage image = new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);
54. Graphics2D g2 = (Graphics2D)image.getGraphics();
55. g2.setColor(this.bgColor);
56. g2.fillRect(0, 0, w, h);
57. return image;
58. }
59. public BufferedImage getImage(){
60. BufferedImage image = createImage();
61. Graphics2D g2 = (Graphics2D)image.getGraphics();
62. StringBuilder sb = new StringBuilder();
63. for(int i= 0;i<4;i++){
64. String s = randomChar()+"";
65. sb.append(s);
66. float x = i*1.0F*w/4;
67. g2.setFont(randomFont());
68. g2.setColor(randomColor());
69. g2.drawString(s, x, h-5);
70. }
71. this.text = sb.toString();
72. drawLine(image);
73. return image;
74. }
75. public String getText(){
76. return text;
77. }
78. public static void output (BufferedImage image,OutputStream out) throws IOException{
79. ImageIO.write(image, "JPEG", out);
80. }
81. }

2.创建验证码的servlet

1. import java.awt.image.BufferedImage;
2. import java.io.IOException;
3. import java.io.PrintWriter;
4. import javax.imageio.ImageIO;
5. import javax.servlet.ServletException;
6. import javax.servlet.annotation.WebServlet;
7. import javax.servlet.http.HttpServlet;
8. import javax.servlet.http.HttpServletRequest;
9. import javax.servlet.http.HttpServletResponse;
10. import util.VerifyCode;
11. @WebServlet("/VerifyCodeServlet")
12. public class VerifyCodeServlet extends HttpServlet {
13. /**
14. * Servlet
15. * @author weiqiang
16. */
17. public void doGet(HttpServletRequest request, HttpServletResponse response)
18. throws ServletException, IOException {
19. VerifyCode vc = new VerifyCode();
20. response.setHeader("Cache-Control", "no-cache");
21. response.setContentType("image/jpeg");
22. BufferedImage bim = vc.getImage();
23. ImageIO.write(bim, "JPEG", response.getOutputStream());
24. String verifycode = vc.getText();
25. request.getSession().setAttribute("verifyCode", verifycode);
26. }
27. public void doPost(HttpServletRequest request, HttpServletResponse response)
28. throws ServletException, IOException {
29. doGet(request, response);
30. }
31. public void destroy(){
32. super.destroy();
33. }
34. public void init() throws ServletException{
35. }
36. }
37. 3.在xml中进行配置
38. servlet>
    <servlet-name>VerifyCodeServlet</servlet-name>
    <servlet-class>cn.com.shxt.servlet.VerifyCodeServlet</servlet-class>
    </servlet>
    <servlet-mapping>
    <servlet-name>VerifyCodeServlet</servlet-name>
    <url-pattern>/VerifyCodeServlet</url-pattern>
    </servlet-mapping>

3.在需要使用验证码的地方使用如下代码：

[html] view plain copy

1. <!--这是看不清刷新一下的函数-->
2. <script>
3. function changeVerifyCode(){
4. document.getElementById("validateCodeImg").src="VerifyCodeServlet?t="+Math.random();
5. }
6. </script>
7. <!-- 这是输入验证码的输入框-->
8. <INPUT id=txtSN size=4 name=txtSN>
9. <!-- 这是显示的验证码，以图片显示-->
10. <!-- src的路劲为servlet的路劲 -->
11. <img src="<%=basePath%>VerifyCodeServlet" border=0 id="validateCodeImg" style="height: 25px; width: 57px"/><a href="#" onclick="changeVerifyCode()">看不清？换一张</a></TD>

4.实际效果如下

String code = request.getParameter("code");
String verifyCode = (String) request.getSession().getAttribute("verifyCode");

else if(!code.equals(verifyCode)){//登陆失败
request.setAttribute("message","验证码错误");
request.getRequestDispatcher("/login.jsp").forward(request, response);

前台的code和session中的验证码进行比较，实现验证码的功能。