android 中添加了读写文件的权限，却报(Permission denied)错误

Question

android 中添加了读写文件的权限，却报open failed: EACCES (Permission denied)
太坑人了！
添加了权限

    //代码部分：
    File file2 = new File(Environment.getExternalStorageDirectory(),"file2.txt");
    file2.setWritable(true);
    file2.setReadable(true);
            FileOutputStream fos = new FileOutputStream(file2);
    fos.write("nihao world".getBytes());

            报错

            java.io.IOException: open failed: EACCES (Permission denied)

com.example.testfile W/System.err: at java.io.File.createNewFile(File.java:939)
com.example.testfile W/System.err: at com.example.testfile.MainActivity.createFile(MainActivity.java:31)