注意：浏览器默认会缓存图片

public static int WIDTH = 120;

public static int HEIGHT = 25;

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html");

//创建内存图像

BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);

//勾勒图像

Graphics graphics = image.getGraphics();

//设置背景

graphics.setColor(Color.WHITE);

graphics.fillRect(0, 0, WIDTH, HEIGHT);

//设置边框

graphics.setColor(Color.BLUE);

graphics.drawRect(1, 1, WIDTH-2, HEIGHT-2);

//画干扰线

graphics.setColor(Colohttp://r.YELLOW);

for(int i=0;i<8;i++){

int xStart = new Random().nextInt(WIDTH);

int yStart = new Random().nextInt(HEIGHT);

int xEnd = new Random().nextInt(WIDTH);

int yEnd = new Random().nextInt(HEIGHT);

graphics.drawLine(xStart, yStart, xEnd, yEnd);

}

//写随机数

graphics.setColor(Color.RED);

int x = 5;

for(int i=0;i<4;i++){

graphics.drawString(new Random().nextInt(9)+"", x, 20);

x+=30;

}