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I'm trying to get from an Android Uri to a byte array.

I have the following code, but it keeps telling me that the byte array is 61 bytes long, even though the file is quite large - so I think it may be turning the Uri string into a byte array, rather than the file :(

  Log.d(LOG_TAG, "fileUriString = " + fileUriString);
  Uri tempuri = Uri.parse(fileUriString);
  InputStream is = cR.openInputStream(tempuri);
  String str=is.toString();
  byte[] b3=str.getBytes();
  Log.d(LOG_TAG, "len of data is " + imageByteArray.length
     + " bytes");

Please can someone help me work out what to do?

The output is "fileUriString = content://media/external/video/media/53" and "len of data is 61 bytes".


is.toString() will give you a String representation of the InputStream instance, not its content.

You need to read() bytes from the InputStream into your array. There's two read methods to do that, read() which reads a single byte at a time, and read(byte[] bytes) which reads bytes from the InputStream into the byte array you pass to it.

Update: to read the bytes given that an InputStream does not have a length as such, you need to read the bytes until there is nothing left. I suggest creating a method for yourself something like this is a nice simple starting point (this is how I would do it in Java at least).

public byte[] readBytes(InputStream inputStream) throws IOException {
  // this dynamically extends to take the bytes you read
  ByteArrayOutputStream byteBuffer = new ByteArrayOutputStream();

  // this is storage overwritten on each iteration with bytes
  int bufferSize = 1024;
  byte[] buffer = new byte[bufferSize];

  // we need to know how may bytes were read to write them to the byteBuffer
  int len = 0;
  while ((len = inputStream.read(buffer)) != -1) {
    byteBuffer.write(buffer, 0, len);

  // and then we can return your byte array.
  return byteBuffer.toByteArray();
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      • 1
    • Thank you. That doesn't solve the problem though, because I have to specify the length of the byte[] array before I supply it, and I can't get that from an InputStream. Any idea how I can work out the length of the data given the Uri?
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    • why do we need to declare a buffer size? could w eput any length and if so, is there no way to put entire contents at once?
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    • @AP257 I'm not sure if it helps, but to read the number of bytes from input stream you can call .available() method

Kotlin way:

private fun readBytes(context: Context, uri: Uri): ByteArray? = 
    context.contentResolver.openInputStream(uri)?.buffered()?.use { it.readBytes() }

In Kotlin, they added convenient extension functions for InputStream like buffered, use, and readBytes.

  • buffered decorates the input stream as BufferedInputStream
  • use handles closing the stream
  • readBytes does the main job of reading the stream and writing into a byte array

Error cases:

  • IOException can occur during the process (like in Java)
  • openInputStream can return null. If you call the method in Java you can easily oversee this. Think about how you want to handle this case.
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while ((len = inputStream.read(buffer)) != -1)

should be

while (inputStream.available() >0 && (len = inputStream.read(buffer)) != -1)

This way read will not block if stream has no available bytes as explained in this answer.

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      • 1
    • Blocking is the correct behaviour if you have only received half the file. Checking availability is a dreadful alternative to checking for end of file.

Sharing my idea :D

private static byte[] getStringFromInputStream(InputStream is) 

    BufferedReader br = null;
    StringBuilder sb = new StringBuilder();
    byte[] bReturn = new byte[0];

    String line;

        br = new BufferedReader(new InputStreamReader(is, "Big5"));
        while ((line = br.readLine()) != null) 
        String sContent = sb.toString();
        bReturn = sContent.getBytes();          
    catch (IOException e) 
        if (br != null) 
            catch (IOException e) 
    return bReturn;
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      • 2
    • InputStreamReader is use Big5 encoding format, because my content have chinese character, you can use UTF-8

if You have an Uri, instead of a regular file name, you should use Content Resolver. Android: Getting a file URI from a content URI?

I tried this, and it works. Uri uri; // it is something, I've got from a file chooser. Of course, I must be sure, that the uri points to a filename, and it is not an image, or audio, or something else...

InputStream is=getContentResolver().openInputStream(uri);
InputStreamReader ir=new InputStreamReader(is);
bu=new BufferedReader(ir);
String s;
while ((s=bu.readLine())!=null){
    //do something with the line...

I've omitted some try-catch-finally from the code, but the most important things are here. The first thing is, that if you have an uri, you cannot use the standard file reader.

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