io问题，求帮助

import android.os.Environment;
import android.util.Log
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
/**
* Created by Administrator on 2016/5/11.
*/
public class FileUtil {
private String SD_PATH;
public String getSD_PATH(){
return SD_PATH;
}
//构造函数
public FileUtil(){
//得到当前外部存储设备的目录
SD_PATH = Environment.getExternalStorageDirectory() + "";
System.out.println(SD_PATH);
}
public File creatSDFile (String fileName) throws IOException{
File file = new File( SD_PATH + fileName);
try {
file.createNewFile();
}catch (IOException e){
e.printStackTrace();
}
return file;
}
public File creatSDDir(String dirName){
File dir = new File(SD_PATH + dirName);
if (!dir.exists()) {
dir.mkdirs();
}
return dir;
}
//判断文件是否存在
public boolean isFileExist(String fileName){
File file = new File(SD_PATH + fileName);
return file.exists();
}
//写入
public File write2SDFromInput(String path,String fileName,InputStream input){
File file = null;
OutputStream output = null;
System.out.println(SD_PATH + path + fileName);
try {
creatSDDir(path);
file =creatSDFile(path + fileName);
output = new FileOutputStream(file);
byte buffer[] = new byte[4*1024];
while ((input.read())!= -1){
output.write(buffer);
}
output.flush();
}catch (Exception e){
Log.e("write2SDFromInput" ,e.getMessage());
}finally {
try {
if (output!=null){
output.close();
}
}catch (Exception e){
Log.e("write2SDFromInput",e.getMessage());
}
}
return file;
}
}
会报错：：：
05-12 11:10:08.773 18511-20969/com.ylqyfw.download_online E/write2SDFromInput: /storage/emulated/0/downloadDir/aaa.doc: open failed: ENOENT (No such file or directory)