JSF_022：使用Servlet动态生成图片验证码 （摘录+整理）

说明：以下程序在JDK 1.7.0 Update 51，Java EE 7 环境下测试通过。

1. Servlet代码

import java.io.IOException;
import java.io.PrintWriter;
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 java.awt.*;
import java.awt.image.BufferedImage;
import java.util.*;
import javax.imageio.ImageIO;
import javax.servlet.http.HttpSession;


@WebServlet(name = "AuthenticationImageServlet", urlPatterns = {"/AuthenticationImageServlet"})
public class AuthenticationImageServlet extends HttpServlet {

    private Font mFont = new Font("Arial Black", Font.PLAIN, 16);

    public void init() throws ServletException {
        super.init();
    }

    Color getRandColor(int fc, int bc) {
        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);
    }

    /**
     * Processes requests for both HTTP GET and POST
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setContentType("image/jpeg");

        int width = 100, height = 18;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

        Graphics g = image.getGraphics();
        Random random = new Random();
        g.setColor(getRandColor(200, 250));
        g.fillRect(1, 1, width - 1, height - 1);
        g.setColor(new Color(102, 102, 102));
        g.drawRect(0, 0, width - 1, height - 1);
        g.setFont(mFont);

        g.setColor(getRandColor(160, 200));
        for (int i = 0; i < 155; i++) {
            int x = random.nextInt(width - 1);
            int y = random.nextInt(height - 1);
            int xl = random.nextInt(6) + 1;
            int yl = random.nextInt(12) + 1;
            g.drawLine(x, y, x + xl, y + yl);
        }
        for (int i = 0; i < 70; i++) {
            int x = random.nextInt(width - 1);
            int y = random.nextInt(height - 1);
            int xl = random.nextInt(12) + 1;
            int yl = random.nextInt(6) + 1;
            g.drawLine(x, y, x - xl, y - yl);
        }

        String sRand = "";
        for (int i = 0; i < 6; i++) {
            String tmp = getRandomChar();
            sRand += tmp;
            g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));
            g.drawString(tmp, 15 * i + 10, 15);
        }

        HttpSession session = request.getSession(true);
        session.setAttribute("rand", sRand);
        g.dispose();
        ImageIO.write(image, "JPEG", response.getOutputStream());
    }

    /**
     * Handles the HTTP GET method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Handles the HTTP POST method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }

    private String getRandomChar() {
        int rand = (int) Math.round(Math.random() * 2);
        long itmp = 0;
        char ctmp = '\u0000';
        switch (rand) {
            case 1:
                itmp = Math.round(Math.random() * 25 + 65);
                ctmp = (char) itmp;
                return String.valueOf(ctmp);
            case 2:
                itmp = Math.round(Math.random() * 25 + 97);
                ctmp = (char) itmp;
                return String.valueOf(ctmp);
            default:
                itmp = Math.round(Math.random() * 9);
                return String.valueOf(itmp);
        }
    }

}

2. JSF 页面代码

<html xmlns="http://www.w3.org/1999/xhtml"

      xmlns:h="http://xmlns.jcp.org/jsf/html">

    <h:head>

        <title>Facelet Title</title>

    </h:head>

    <h:body>

        <img src="AuthenticationImageServlet" id="authImg" />

    </h:body>

</html>

3. 运行效果