动态生成验证码

1、创建图片缓冲区
2、设置其宽高
3、得到这个图片的绘制环境（得到画笔）
4、保存图片

BufferedImage bi = new BufferedImage(80,35,BufferedImage.TYPE_INT_RGB);


Graphics2D g = (Graphics2D) bi.getGraphics();
g.setColor(Color.WHITE);
g.fillRect(0, 0,80,35);
g.setColor(Color.RED);
g.drawString("HELLO", 2, 35-2);

try {
     ImageIO.write(bi, "JPEG", new FileOutputStream("xxx.jpg"));
} catch (FileNotFoundException e) {
     e.printStackTrace();
} catch (IOException e) {
     e.printStackTrace();
}

完整验证码：

package com.image;

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 {
	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  = 3;//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);
	}

public static void main(String[] args) {
		VerifyCode v = new VerifyCode();
		try {
			output(v.getImage(), new FileOutputStream("xxx.jpg"));
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		System.out.println(v.getText());
	}
}