jQuery调用Java后台接口实现验证码的刷新

1、后台Java数据
　　

public class verify_code extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("Pragma", "No-cache");
        resp.setHeader("Cache-Control", "no-cache");
        resp.setDateHeader("Expires", 0);
        resp.setContentType("image/jpeg");

        //生成随机字串
        String verifyCode = VerifyCodeUtil.generateVerifyCode(4);
        //存入会话session
        HttpSession session = req.getSession(true);
        session.setAttribute("verifyCode", verifyCode.toLowerCase());
        //生成图片
        int w = 200, h = 80;
        VerifyCodeUtil.outputImage(w, h, resp.getOutputStream(), verifyCode);
    }
}

2、jQuery从后台得到接口，实现局部刷新

function code() {
    $('.code').attr("src", "/verify_code?a=" + Math.random());
    console.log('update');
}