Concatenate ByteArrayOutputStream

Question

public byte[] toByteArray() {
    try {
        ByteArrayOutputStream objectStream = dataObject.toByteArrayOutputStream();
        DataOutputStream dout = new DataOutputStream(objectStream);
        dout.writeUTF(recordid);    

        dout.close();
        objectStream.close();
        return objectStream.toByteArray();
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}

There is a problem with the code above. I first create an objectStream (in another class). And then I manually add the recordid to the ByteArrayOutputStream. But is there a way to first add the recordId & then append the ByteArrayOutputStream to it? Basically I have 2 ByteArrayoutputStreams which need to be concatenated (and remain a ByteArrayOutputStream).

edit: My new version should work but it does not. When I print out the hashcode of dout, it is the same before and after the flush. It's like it stays empty? Is that possible?

public byte[] toByteArray() {
        try {

            ByteArrayOutputStream realOutputStream = new ByteArrayOutputStream();
            DataOutputStream dout = new DataOutputStream(realOutputStream);
            dout.writeUTF(dataObject.getClass().toString());
            dout.writeUTF(recordid);
            System.out.println("Recordid: " + recordid + "|" +  dout.hashCode());
            dout.flush();
            System.out.println("Recordid: " + recordid + "|" +  dout.hashCode());

            ByteArrayOutputStream objectStream = dataObject.toByteArrayOutputStream();
            dout.write(objectStream.toByteArray());

            dout.close();
            objectStream.close();
            return objectStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

score 5 · Accepted Answer · answered Jan 19 '11 at 13:25

5

try the following to place the recordid first.

ByteArrayOutputStream objectStream = new ByteArrayOutputStream();
DataOutputStream dout = new DataOutputStream(objectStream);
dout.writeUTF(recordid);    
dout.write(dataObject.toByteArrayOutputStream().toByteArray());

answered Jan 19 '11 at 13:25

Peter Lawrey

525,659
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I have tried this (even with dout.flush() between the writeUTF and the write. But the recordid is not added to the stream :S – Vincent Jan 19 '11 at 13:50
This won't alter the original stream, you can't prepend data to that. – Peter Lawrey Jan 19 '11 at 14:19

score 2 · Answer 2 · answered Jan 19 '11 at 13:24

2

The method writeTo() will let you append the contents of a ByteArrayOutputStream to any other OutputStream.

answered Jan 19 '11 at 13:24

biziclop

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77
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1

This method is not present in J2ME: http://download.oracle.com/javame/config/cldc/ref-impl/cldc1.1/jsr139/java/io/ByteArrayOutputStream.html – BalusC Jan 19 '11 at 13:26
@BalusC How was I to know it was J2ME? In J2ME you can simply say `baos1.write( baos2.toByteArray(), 0, baos2.toByteArray().length );` – biziclop Jan 19 '11 at 13:29
The OP explicitly commented it. – BalusC Jan 19 '11 at 13:30
@BalusC Yes, a bit later than I started writing the answer though. The OP didn't mention it in the question and didn't tag it properly either. – biziclop Jan 19 '11 at 13:37

score 0 · Answer 3 · answered Jan 19 '11 at 13:23

0

I don't know what the API of ByteArrayOutputStream on J2ME is like but try:

ByteArrayOutputStream realOutput = new ByteArrayOutputStream();
DataOutputStream dout = new DataOutputStream(realOutput);
dout.writeUTF(recordid);
dout.flush();

ByteArrayOutputStream objectStream = dataObject.toByteArrayOutputStream();
objectStream.writeTo(realOutput);

return realOutput.toByteArray();

answered Jan 19 '11 at 13:23

Jon Skeet

1,421,763
867
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9,194

1

For your reference, API docs are in JSR139: http://download.oracle.com/javame/config/cldc/ref-impl/cldc1.1/jsr139/index.html – BalusC Jan 19 '11 at 13:26

score 0 · Answer 4 · answered Jan 19 '11 at 14:02

You could write dataObject and recordid in the current (wrong) order then rotate them into place:

public byte[] toByteArray() {
    try {
        ByteArrayOutputStream objectStream = dataObject.toByteArrayOutputStream();
        int pos = objectStream.size();
        DataOutputStream dout = new DataOutputStream(objectStream);
        dout.writeUTF(recordid);    
        dout.close();
        objectStream.close();
        byte[] array = return objectStream.toByteArray();
        rotate(array, pos);
        return array;
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}

private static void rotate(byte[] array, int pos) {
    reverse(array, 0, pos);
    reverse(array, pos, array.length);
    reverse(array, 0, array.length);
}

private static void reverse(byte[] array, int start, int end) {
    while (start < --end) {
        byte t = array[start];
        array[start] = array[end];
        array[end] = t;
        ++ start;
    }
}

Concatenate ByteArrayOutputStream

4 Answers4