为什么我的会报错误文件路径找不到？

java.io.FileNotFoundException: E:\ (系统找不到指定的路径。)

at java.io.RandomAccessFile.open(Native Method)

at java.io.RandomAccessFile.<init>(RandomAccessFile.java:212)

at javax.imageio.stream.FileImageOutputStream.<init>(FileImageOutputStream.java:53)

at com.sun.imageio.spi.FileImageOutputStreamSpi.createOutputStreamInstance(FileImageOutputStreamSpi.java:37)

at javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:393)

at javax.imageio.ImageIO.write(ImageIO.java:1514)

at com.imooc.qrcode.CreateQRCode.main(CreateQRCode.java:66)

Exception in thread "main" java.lang.NullPointerException

at javax.imageio.ImageIO.write(ImageIO.java:1523)

at com.imooc.qrcode.CreateQRCode.main(CreateQRCode.java:66)

package com.imooc.qrcode;

import java.awt.Color;

import java.awt.Graphics2D;

import java.awt.image.BufferedImage;

import java.io.File;

import java.io.IOException;

import javax.imageio.ImageIO;

import com.swetake.util.Qrcode;

public class CreateQRCode {

/**

* @param args

* @throws Exception 

*/

public static void main(String[] args) throws Exception {

// TODO Auto-generated method stub

Qrcode x = new Qrcode();

x.setQrcodeErrorCorrect('M');//纠错等级

x.setQrcodeEncodeMode('B');//N代表数字，A代表a-Z，B代表其他字符

x.setQrcodeVersion(7); //版本

String qrData ="www.imooc.com";

int width = 300;

int height = 300;

//这是基于Java的JUI的画图工具来做的。

BufferedImage bufferedImage = new BufferedImage(width, height,

BufferedImage.TYPE_INT_BGR);

//画图工具，java的

Graphics2D gs = bufferedImage.createGraphics();

//背景颜色

gs.setBackground(Color.WHITE);

//图片颜色

gs.setColor(Color.BLACK);

//画板的内容

gs.clearRect(0, 0, width, height);  //0,0指的是从画板的0开始

//偏移量,如果有时候不加偏移量，有时就导致我们解析错误。

int pixoff =2;

//这块是往我们的画板里面填充内容

byte[] d = qrData.getBytes("gb2312");   //如果有汉字的话，要转成gb2312

if(d.length > 0 && d.length < 120){

boolean[][] s = x.calQrcode(d);

for(int i=0; i<s.length; i++){

for(int j=0;j<s.length;j++){

if(s[j][i]){

gs.fillRect(j*3+pixoff, i*3+pixoff, 3, 3);

}

}

}

}

//结束我们的输出

gs.dispose();

bufferedImage.flush();

ImageIO.write(bufferedImage, "png", new File("E:/"));

}

}