How to create nested folders and file in Context.MODE_PRIVATE?

问题

I have a requirement where files and folders are required to be written in nested structure using Context.MODE_PRIVATE.

I found that we can create file using openFileOutput(FILENAME, Context.MODE_PRIVATE); and was able to create files using this method.But later on I found that using this method I can not create a nested file structure i.e for

openFileOutput("foo/myText.txt", Context.MODE_PRIVATE);

exception is thrown:

java.lang.IllegalArgumentException: File foo/myText.txt contains a path separator

May be because it expects only a fileName & not a filepath and also documentation says

Open a private file associated with this Context's application package for writing.

Then I found that getFilesDir() returns Context's application package where I can create files using the normal Java File I/O.But I don't know the permissions under which it is created i.e whether it is MODE_APPEND,MODE_PRIVATE,MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE.

So, I have following questions:-

1. How do I create nested file structure using openFileOutput() method under MODE_PRIVATE(if it's possible)?

2. If openFileOutput() is not applicable to create a nested structure,then is it safe to use getFilesDir() and Java File I/O combination for my requirement? What is the permission for the files created using this way?

回答1:

You need to create foo directory first then create file inside that dir.

Use getDir(String name, int mode) to create directory into internal memory. The method Retrieve, creating if needed, a new directory in which the application can place its own custom data files. You can use the returned File object to create and access files in this directory.

---

For example

// Create directory into internal memory;
File mydir = context.getDir("mydir", Context.MODE_PRIVATE);
// Get a file myfile within the dir mydir.
File fileWithinMyDir = new File(mydir, "myfile"); 
// Use the stream as usual to write into the file.
FileOutputStream out = new FileOutputStream(fileWithinMyDir); 

---

So your need to write your code as

// Create foo directory into internal memory;
File mydir = getDir("foo", Context.MODE_PRIVATE);
// Get a file myText.txt within the dir foo.
File fileWithinMyDir = new File(mydir, "myText.txt"); 
// Use the stream as usual to write into the file.
try {
    FileOutputStream out = new FileOutputStream(fileWithinMyDir);
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

to create foo/myText.txt into internal storage.

---

For nested directories, you should use normal java method. Like

new File(parentDir, "childDir").mkdir();

So updated example should be

// Create directory into internal memory;
File mydir = getDir("mydir", Context.MODE_PRIVATE);

// Create sub-directory mysubdir
File mySubDir = new File(mydir, "mysubdir");
mySubDir.mkdir();

// Get a file myfile within the dir mySubDir.
File fileWithinMyDir = new File(mySubDir, "myfile"); 
// Use the stream as usual to write into the file.
FileOutputStream out = new FileOutputStream(fileWithinMyDir);

回答2:

public OutputStream openFile(String absolutePath) throws FileNotFoundException {
  File file = new File(absolutePath);
  new File(file.getParent()).mkdirs();

  return new FileOutputStream(absolutePath);
}

public OutputStream openInternalFile(String relativePath) throws FileNotFoundException {
  String rootPath = this.getFilesDir().getPath();
  File file = new File(rootPath, relativePath);
  return openFile(file.getAbsolutePath());
}

This is what I came up which covers your use case. You can either pass the absolutePath or relativePath. behind the scene it does create a nested folders inside internal storage and returns back an OutputStream which you can start write into it.

来源：https://stackoverflow.com/questions/21326331/how-to-create-nested-folders-and-file-in-context-mode-private