两字符串相等却回来falst~

两字符串相等却返回falst~??
最近学习Session~做了一个验证码~
我试图这样比较
if ("checknum".equals(check)){
            out.println("<h1>" + "您输入的是正确的" + "</h1>");
        }
但是一直是falst~~

package org.timepower.Session;


import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * Created by timepower on 14-6-22.
 */
@WebServlet("/img.do")
public class randomimg extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        int width = 60;
        int height = 20;
        BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        Graphics g = bi.getGraphics();
        g.setColor(Color.black);

        g.fillRect(0, 0, width, height);

        g.setFont(new Font("XHei", Font.BOLD,18));

        String rand = randomNum();
        g.setColor(new Color(160,0,0));
        g.drawString(rand,7,15);

        HttpSession session = req.getSession();
        session.setAttribute("checknum",rand);

        ServletOutputStream sos = res.getOutputStream();
        ImageIO.write(bi, "jpeg", sos);
        sos.close();
    }
    //随机数方法
    public String randomNum(){
        Random ran = new Random();
        int output = ran.nextInt(10000);
        String temp = "";
        if (output < 1000){
            output = output + 1000;
        }
        temp = output + temp;
        return temp;
    }
}

package org.timepower.Session;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Created by timepower on 14-6-26.
 */
@WebServlet("/checkimg.do")
public class Checkimg extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        String check = req.getParameter("number");
        HttpSession session = req.getSession();
        session.getAttribute("checknum");

        PrintWriter out = res.getWriter();
        if ("checknum".equals(check)){
            out.println("<h1>" + "您输入的是正确的" + "</h1>");
        }else{
            out.println("<style type=\"text/css\">\n" +
                    "        body {\n" +
                    "            width: 800px;\n" +