关于登入（用户名，密码，验证码）

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import sun.misc.BASE64Encoder;
import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

public class RandomValidateCodeUtil {
public static final String RANDOMCODEKEY = "randomcode_key";//放到session中的key
private Random random = new Random();
private String randString = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";//随机产生的字符串
private int width = 85;//图片宽
private int height = 36;//图片高
private int lineSize = 40;//干扰线数量
private int stringNum = 4;//随机产生字符数量

private static final Logger logger = LoggerFactory.getLogger(RandomValidateCodeUtil.class);

/**
 * 生成随机图片
 */
public Map<String,String> getRandcode() {
    // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
    BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR);
    Graphics g = image.getGraphics();// 产生Image对象的Graphics对象,改对象可以在图像上进行各种绘制操作
    g.fillRect(0,width,height);//图片大小
    g.setFont(new Font("Times New Roman",Font.ROMAN_BASELINE,18));//字体大小
    g.setColor(getRandColor(110,133));//字体颜色
    // 绘制干扰线
    for (int i = 0; i <= lineSize; i++) {
        drowLine(g);
    }
    // 绘制随机字符
    String randomString = "";
    for (int i = 1; i <= stringNum; i++) {
        randomString = drowString(g,randomString,i);
    }

    logger.info(randomString);
    //将生成的随机字符串保存到session中
    //session.removeAttribute(RANDOMCODEKEY);
    //session.setAttribute(RANDOMCODEKEY,randomString);
    g.dispose();
    String base64 = null;
    try {
        // 将内存中的图片通过流动形式输出到客户端
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(image,"JPEG",baos);//图片格式

        byte[] bytes = baos.toByteArray();

        base64 =  new BASE64Encoder().encodeBuffer(bytes).trim();
    } catch (Exception e) {
        logger.error("将内存中的图片通过流动形式输出到客户端失败>>>>   ",e);
    }

    Map<String,String> map = new HashMap<String,String>();
    map.put("num",randomString);
    map.put("pic",base64);
    return map;
}

/*
 * 获得字体
 */
private Font getFont(){
    return new Font("Fixedsys",Font.CENTER_BASELINE,18);
}
/*
 * 获得颜色
 */
private Color getRandColor(int fc,int bc){
    if(fc > 255)
        fc = 255;
    if(bc > 255)
        bc = 255;
    int r = fc + random.nextInt(bc-fc-16);
    int g = fc + random.nextInt(bc-fc-14);
    int b = fc + random.nextInt(bc-fc-18);
    return new Color(r,g,b);
}
/*
 * 绘制字符串
 */
private String drowString(Graphics g,String randomString,int i){
    g.setFont(getFont());
    g.setColor(new Color(random.nextInt(101),random.nextInt(111),random.nextInt(121)));
    String rand = String.valueOf(getRandomString(random.nextInt(randString.length())));
    randomString +=rand;
    g.translate(random.nextInt(3),random.nextInt(3));
    g.drawString(rand,13*i,16);
    return randomString;
}
/*
 * 绘制干扰线
 */
private void drowLine(Graphics g){
    int x = random.nextInt(width);
    int y = random.nextInt(height);
    int xl = random.nextInt(13);
    int yl = random.nextInt(15);
    g.drawLine(x,y,x+xl,y+yl);
}
/*
 * 获取随机的字符
 */
public String getRandomString(int num){
    return String.valueOf(randString.charAt(num));
}

}