常用类

public class VerifyCode {
private int      w         = 70;
private int      h         = 35;
private Random   r         = new Random();
// {"宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312"}
private String[] fontNames = {"宋体", "华文楷体", "黑体", "微软雅黑", "楷体_GB2312"};
// 可选字符
private String   codes     = "23456789abcdefghjkmnopqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ";
// 背景色
private Color    bgColor   = new Color(255, 255, 255);
// 验证码上的文本
private String   text ;

// 生成随机的颜色
private Color randomColor () {
    int red = r.nextInt(150);
    int green = r.nextInt(150);
    int blue = r.nextInt(150);
    return new Color(red, green, blue);
}

// 生成随机的字体
private Font randomFont () {
    int index = r.nextInt(fontNames.length);
    String fontName = fontNames[index];//生成随机的字体名称
    int style = r.nextInt(4);//生成随机的样式, 0(无样式), 1(粗体), 2(斜体), 3(粗体+斜体)
    int size = r.nextInt(5) + 24; //生成随机字号, 24 ~ 28
    return new Font(fontName, style, size);
}

// 画干扰线
private void drawLine (BufferedImage image) {
    int num  = 4;//一共画3条
    Graphics2D g2 = (Graphics2D)image.getGraphics();
    for(int i = 0; i < num; i++) {//生成两个点的坐标，即4个值
        int x1 = r.nextInt(w);
        int y1 = r.nextInt(h);
        int x2 = r.nextInt(w);
        int y2 = r.nextInt(h);
        g2.setStroke(new BasicStroke(1.5F));
        g2.setColor(Color.BLUE); //干扰线是蓝色
        g2.drawLine(x1, y1, x2, y2);//画线
    }
}

// 随机生成一个字符
private char randomChar () {
    int index = r.nextInt(codes.length());
    return codes.charAt(index);
}

// 创建BufferedImage
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;
}

// 调用这个方法得到验证码
public BufferedImage getImage () {
    BufferedImage image = createImage();//创建图片缓冲区
    Graphics2D g2 = (Graphics2D)image.getGraphics();//得到绘制环境
    StringBuilder sb = new StringBuilder();//用来装载生成的验证码文本
    // 向图片中画4个字符
    for(int i = 0; i < 4; i++)  {//循环四次，每次生成一个字符
        String s = randomChar() + "";//随机生成一个字母
        sb.append(s); //把字母添加到sb中
        float x = i * 1.0F * w / 4; //设置当前字符的x轴坐标
        g2.setFont(randomFont()); //设置随机字体
        g2.setColor(randomColor()); //设置随机颜色
        g2.drawString(s, x, h-5); //画图
    }
    this.text = sb.toString(); //把生成的字符串赋给了this.text
    drawLine(image); //添加干扰线
    return image;
}

// 返回验证码图片上的文本
public String getText () {
    return text;
}

// 保存图片到指定的输出流
public static void output (BufferedImage image, OutputStream out)
        throws IOException {
    ImageIO.write(image, "JPEG", out);
}

测试

@Test
public void fun2() throws FileNotFoundException, IOException {
    VerifyCode vc = new VerifyCode();
    BufferedImage bi = vc.getImage();
    VerifyCode.output(bi, new FileOutputStream("F:/xxx.jpg"));
    
    System.out.println(vc.getText());
}