How to convert OutputStream to String in Java (Android)?

Question

I am trying to read the string that I get inside an outputStream that in turn is written there by a ftp - from a ftp server.

I'm stuck at this problem for about 2 hours and I find it hard to belive that it's so difficult to solve.

Is there any nice solution for my problem?

Here's the relevant code:

boolean success = false;
        OutputStream outputStream = null;
        try {
            outputStream = new BufferedOutputStream(new FileOutputStream(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/" + fileName));
            success = ftp.retrieveFile("/ViatorAndroid/" + fileName, outputStream);
        } catch (Exception e) {
            Log.d("FTPDownloadLatestVersion", "e = " + e.getMessage() + " " + Arrays.toString(e.getStackTrace()));
        }
        outputStream.close();
        if (success) {
            
            String versionNumberString = outputStream.getString(); // ??? I need here a way to get the string inside this output stream. Any clue how???
            int versionNumber = Integer.parseInt(versionNumberString);
            Log.d("FTPGetLastestVersionCode", "VersionNumber = " + versionNumber);
            return BuildConfig.VERSION_CODE < versionNumber;
        }

Do you want the content in both the file and as a string? — Joachim Sauer
– Joachim Sauer, Commented May 7, 2021 at 13:20
No. I have the outputStream variable containing some kind of string. I need to have that content from that stream inside a string. — user15381310
– user15381310, Commented May 7, 2021 at 13:22
An output stream doesn't (normally) contain a string. It's a handle to "some place" that you can write stuff to. Unless that "some place" is explicitly a byte buffer or similar, it doesn't actually store what its written to. As an example: A FileOutputStream doesn't remember what you wrote to it. It simply writes it to a file and then forgets about it. You can construct a ByteArrayOutputStream where the "some place" is a byte array, but pretty much everything else is just a pointer to some other place. — Joachim Sauer
– Joachim Sauer, Commented May 7, 2021 at 13:27

JP Moresmau · Accepted Answer · 2021-05-07 13:56:25Z

1

If you just want the content in a string, you build a ByteArrayOutputStream that will collect all the bytes written to it, and then turn this into a String.

Something like

try (ByteArrayOutputStream baos=new ByteArrayOutputStream()){
    boolean success = ftp.retrieveFile("/ViatorAndroid/" + fileName, baos);
    if (success){
       String versionNumberString = new String(baos.toByteArray(),StandardCharsets.UTF_8);
       ...
    }
}

answered May 7, 2021 at 13:56

JP Moresmau

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