Android读写应用文件

Android读写应用自己的文件，不需要声明权限。

 写文件

void writeFile(String filename, String s) {
    try {
        FileOutputStream FOS = openFileOutput(filename, Context.MODE_PRIVATE);
        FOS.write(s.getBytes());
        FOS.close();
    } catch (Exception e) {
        Log.e(Thread.currentThread().getStackTrace()[2] + "", e.toString());
    }
}

读文件

String readFile(String filename) {
    String s = "";
    try {
        FileInputStream FIS = new FileInputStream(filename);        
        int length = FIS.available();    
        byte[] bytes = new byte[length];
        FIS.read(bytes);
        s = new String(bytes);
        FIS.close();
    } catch (Exception e) {
        Log.e(Thread.currentThread().getStackTrace()[2] + "", e.toString());
    }
    return s;
}

Android Studio 的 Device File Explorer 查看，写文件成功，读取文件报错：

java.io.FileNotFoundException: cache: open failed: EACCES (Permission denied)

百思不得其解，最后终于发现了问题了：

FileInputStream FIS = new FileInputStream(filename);
改成
FileInputStream FIS = openFileInput(filename);

这是谁把我带坑里去了？！