Android内部存储指定多级目录下保存文件的实现方法咨询

Great question! To save your file to files/Somefolder/otherfolderchild/filename.txt, you do need to create the parent directories first—Android's built-in openFileOutput() method can't automatically create nested subdirectories for you. If you try to use it with a path containing subdirectories directly, you'll get an IOException because the directories don't exist yet.

Here's how to modify your existing MainActivity.java code to achieve this:

Modified Write Button Method #

This code first creates the nested directory structure, then writes your file to the target path:

// write text to file
public void WriteBtn(View v) {
    // Define your nested directory path and target filename
    String subDirPath = "Somefolder/otherfolderchild";
    String fileName = "filename.txt";
    
    // Get the root "files" directory of your app's internal storage
    File rootFilesDir = getFilesDir();
    // Create a File object for the nested directory structure
    File targetDir = new File(rootFilesDir, subDirPath);
    
    // Create all missing parent directories (if they don't exist)
    if (!targetDir.exists()) {
        boolean dirsCreated = targetDir.mkdirs();
        if (!dirsCreated) {
            Toast.makeText(getBaseContext(), "Failed to create subdirectories!", Toast.LENGTH_SHORT).show();
            return;
        }
    }
    
    // Create a File object for the target file
    File targetFile = new File(targetDir, fileName);
    
    // Write content to the file
    try {
        FileOutputStream fileout = new FileOutputStream(targetFile);
        OutputStreamWriter outputWriter = new OutputStreamWriter(fileout);
        outputWriter.write(textmsg.getText().toString());
        outputWriter.close();
        // Display success message
        Toast.makeText(getBaseContext(), "File saved successfully!", Toast.LENGTH_SHORT).show();
    } catch (Exception e) {
        e.printStackTrace();
        Toast.makeText(getBaseContext(), "Error saving file!", Toast.LENGTH_SHORT).show();
    }
}

Modified Read Button Method #

Update the read logic to match the new file path:

// Read text from file
public void ReadBtn(View v) {
    String subDirPath = "Somefolder/otherfolderchild";
    String fileName = "filename.txt";
    
    File rootFilesDir = getFilesDir();
    // Point to the target file in the nested directory
    File targetFile = new File(new File(rootFilesDir, subDirPath), fileName);
    
    // Reading text from file
    try {
        FileInputStream fileIn = new FileInputStream(targetFile);
        InputStreamReader InputRead = new InputStreamReader(fileIn);
        char[] inputBuffer = new char[READ_BLOCK_SIZE];
        String s = "";
        int charRead;
        
        while ((charRead = InputRead.read(inputBuffer)) > 0) {
            String readstring = String.copyValueOf(inputBuffer, 0, charRead);
            s += readstring;
        }
        InputRead.close();
        textmsg.setText(s);
    } catch (Exception e) {
        e.printStackTrace();
        Toast.makeText(getBaseContext(), "Error reading file!", Toast.LENGTH_SHORT).show();
    }
}

Key Notes #

• getFilesDir(): Returns the absolute path to your app's private internal storage directory (/data/data/com.bla.smthing/files), which is the "files" folder you view in Android Studio's Device File Explorer.
• mkdirs(): Unlike mkdir() (which only creates a single directory level), mkdirs() creates all missing parent directories in the path—critical for nested folders like Somefolder/otherfolderchild.
• No extra permissions needed: Since we're using your app's private internal storage, Android automatically grants access without needing WRITE_EXTERNAL_STORAGE or similar permissions.

After making these changes, you'll find your file at exactly the path you wanted: files/Somefolder/otherfolderchild/filename.txt in Android Studio's file manager.

内容的提问来源于stack exchange，提问作者Rupesh Kumar