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：

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;

import javax.imageio.ImageIO;



public class VerifyCode {
    /**
     *楠岃瘉鐮�
     * @author 瑕冧匠鍗�
     */

    private int w = 50;
    private int h = 25;
    private Random r = new Random();
    private String[] fontNames = {"瀹嬩綋","鍗庢枃妤蜂綋","榛戜綋","寰�蒋闆呴粦","妤蜂綋_GB2312"};
    private String codes = "23456789abcdefghjkmnpqrstuvwxyzABCEFGHIJKLMNPQRSTUVWXYZ";
    private Color bgColor = new Color(255,255,255);
    private String text;

    private Color randomColor(){
        int red = r.nextInt(200);
        int green = r.nextInt(200);
        int blue = r.nextInt(200);
        return new Color(red,green,blue);
    }

    private Font randomFont(){
        int index = r.nextInt(fontNames.length);
        String fontName = fontNames[index];
        int style = r.nextInt(4);
        int size = r.nextInt(6)+15;
        return new Font(fontName,style,size);
        }
    private void drawLine(BufferedImage image){
        int num = 3;
        Graphics2D g2 = (Graphics2D)image.getGraphics();
        for(int i=0;i<num;i++){
            int x1 = r.nextInt();
            int y1 = r.nextInt();
            int x2 = r.nextInt();
            int y2 = r.nextInt();
            g2.setStroke(new BasicStroke(1.5F));
            g2.setColor(Color.BLUE);
            g2.drawLine(x1,y1,x2,y2);
        }
    }
    private char randomChar(){
        int index = r.nextInt(codes.length());
        return codes.charAt(index);
    }
    private BufferedImage createImage(){
        BufferedImage image = new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = (Graphics2D)image.getGraphics();
        g2.setColor(this.bgColor);
        g2.fillRect(0, 0, w, h);
        return image;
    }
    public BufferedImage getImage(){
        BufferedImage image = createImage();
        Graphics2D g2 = (Graphics2D)image.getGraphics();
        StringBuilder sb = new StringBuilder();
        for(int i= 0;i<4;i++){
            String s = randomChar()+"";
            sb.append(s);
            float x = i*1.0F*w/4;
            g2.setFont(randomFont());
            g2.setColor(randomColor());
            g2.drawString(s, x, h-5);
        }
        this.text = sb.toString();
        drawLine(image);
        return image;
    }
    public String getText(){
    return text;
    }
    public static void output (BufferedImage image,OutputStream out) throws IOException{
        ImageIO.write(image, "JPEG", out);
    }
}

2.创建验证码的servlet

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import util.VerifyCode;

@WebServlet("/VerifyCodeServlet")
public class VerifyCodeServlet extends HttpServlet {

    /**
     * Servlet
     * @author weiqiang
     */

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

        VerifyCode vc = new VerifyCode();
        response.setHeader("Cache-Control", "no-cache");
        response.setContentType("image/jpeg");
        BufferedImage bim = vc.getImage();
        ImageIO.write(bim, "JPEG", response.getOutputStream());
        String verifycode = vc.getText();
        request.getSession().setAttribute("verifyCode", verifycode);
    }

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

}
3.在xml中进行配置
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：

<!--这是看不清刷新一下的函数-->
<script>
function changeVerifyCode(){
    document.getElementById("validateCodeImg").src="VerifyCodeServlet?t="+Math.random();

}
</script>
<!-- 这是输入验证码的输入框-->
<INPUT id=txtSN size=4 name=txtSN>
<!-- 这是显示的验证码，以图片显示-->
<!-- src的路劲为servlet的路劲 -->
                  <img src="<%=basePath%>VerifyCodeServlet" border=0 id="validateCodeImg" style="height: 25px;  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。