实现同步加载验证码和用户名是否存在的判断通过Ajax

1.验证码工具类

package com.syh.utils;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
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;
import javax.servlet.http.HttpSession;

public class ValidateCodeServlet extends HttpServlet {
	
	private static final long serialVersionUID = 1L;

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		createCode(request);
		write(response.getOutputStream());
	}
	
    // 图片的宽度
    private int width = 160;
    // 图片的高度
    private int height = 28;
    // 要输入验证码的数量
    private int codeCount = 4;
    // 验证码上面的模糊线
    private int lineCount = 150;
    // 验证码，要和用户输入的对比
    private String code = null;

    private BufferedImage buffImg = null;

    private char[] codeSequence = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R',
            'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '1', '2', '3', '4', '5', '6', '7', '8', '9' };


    public void createCode(HttpServletRequest request) {
        int x = 0, fontHeight = 0, codeY = 0;
        int red = 0, green = 0, blue = 0;

        x = width / (codeCount + 2);
        fontHeight = height - 2;
        codeY = height - 4;

        buffImg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = buffImg.createGraphics();
        Random random = new Random();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        Font font = new Font("Fixedsys", Font.BOLD, fontHeight);
        g.setFont(font);
        for (int i = 0; i < lineCount; i++) {
            int xs = random.nextInt(width);
            int ys = random.nextInt(height);
            int xe = xs + random.nextInt(width / 8);
            int ye = ys + random.nextInt(height / 8);
            red = random.nextInt(255);
            green = random.nextInt(255);
            blue = random.nextInt(255);
            g.setColor(new Color(red, green, blue));
            g.drawLine(xs, ys, xe, ye);
        }

        StringBuffer randomCode = new StringBuffer();
        for (int i = 0; i < codeCount; i++) {
            String strRand = String.valueOf(codeSequence[random.nextInt(codeSequence.length)]);
            red = random.nextInt(255);
            green = random.nextInt(255);
            blue = random.nextInt(255);
            g.setColor(new Color(red, green, blue));
            g.drawString(strRand, (i + 1) * x, codeY);
            randomCode.append(strRand);
        }

        code = randomCode.toString();
        HttpSession session = request.getSession();
        session.setAttribute("code", code);
    }

    public void write(String path) throws IOException {
        OutputStream sos = new FileOutputStream(path);
        this.write(sos);
    }

    public void write(OutputStream sos) throws IOException {
        ImageIO.write(buffImg, "png", sos);
        sos.close();
    }

    public BufferedImage getBuffImg() {
        return buffImg;
    }

    public String getCode() {
        return code;
    }
}
package com.syh.utils;

import java.