验证码

/**
* 生成验证码
*/
public void captcha() {
try {
response.setContentType("image/jpeg");
String captcha = drawImg(response.getOutputStream());
session.setAttribute("captcha", captcha);
} catch (IOException e) {
e.printStackTrace();
}

}

/**
* 绘制验证码
*/
private String drawImg(OutputStream output) {
String code = "";
for (int i = 0; i < 4; i++) {
code += randomChar();
}
int width = 70;
int height = 25;
BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);
Font font = new Font("Times New Roman", Font.PLAIN, 20);
Graphics2D g = bi.createGraphics();
g.setFont(font);
Color color = new Color(66, 2, 82);
g.setColor(color);
g.setBackground(new Color(226, 226, 240));
g.clearRect(0, 0, width, height);
FontRenderContext context = g.getFontRenderContext();
Rectangle2D bounds = font.getStringBounds(code, context);
double x = (width - bounds.getWidth()) / 2;
double y = (height - bounds.getHeight()) / 2;
double ascent = bounds.getY();
double baseY = y - ascent;
g.drawString(code, (int) x, (int) baseY);
g.dispose();
try {
ImageIO.write(bi, "jpg", output);
} catch (IOException e) {
e.printStackTrace();
}
return code;
}

/**
* 验证码随机生成数据源
*/
private char randomChar() {
Random r = new Random();
String s = "ABCDEFGHJKLMNPRSTUVWXYZ0123456789";
return s.charAt(r.nextInt(s.length()));
}