How to Read and Write Strings to Files in Android?

Read/Write a String from/to a File in Android

Reading and writing strings to and from files is a fundamental operation in Android development. This article will demonstrate how to accomplish these tasks using the operating system's built-in file I/O methods.

Writing a String to a File

To save a text string to an internal storage file, follow these steps:

1. Create an OutputStreamWriter object using openFileOutput() and specify the file name and mode.
2. Write the string to the OutputStreamWriter using write().
3. Close the OutputStreamWriter.

Reading a String from a File

To retrieve the string from the saved file, follow these steps:

1. Create an InputStream object using openFileInput().
2. Create an InputStreamReader object using the InputStream.
3. Create a BufferedReader object using the InputStreamReader.
4. Read lines from the file using readLine().
5. Append the lines to a StringBuilder object.
6. Close the InputStream.

Example Code

Here's an example code snippet that demonstrates the aforementioned operations:

Writing:

private void writeToFile(String data, Context context) {
    try {
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(context.openFileOutput("config.txt", Context.MODE_PRIVATE));
        outputStreamWriter.write(data);
        outputStreamWriter.close();
    } catch (IOException e) {
        Log.e("Exception", "File write failed: " + e.toString());
    }
}

Reading:

private String readFromFile(Context context) {

    String ret = "";

    try {
        InputStream inputStream = context.openFileInput("config.txt");

        if (inputStream != null) {
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String receiveString = "";
            StringBuilder stringBuilder = new StringBuilder();

            while ((receiveString = bufferedReader.readLine()) != null) {
                stringBuilder.append("\n").append(receiveString);
            }

            inputStream.close();
            ret = stringBuilder.toString();
        }
    } catch (FileNotFoundException e) {
        Log.e("login activity", "File not found: " + e.toString());
    } catch (IOException e) {
        Log.e("login activity", "Can not read file: " + e.toString());
    }

    return ret;
}

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