How to convert outputStream to a byte array?

Question

How can I convert an OutputStream to a byte array? I have found that first I need to convert this OutputStream to a ByteArrayOutputStream. There is only write() method in this OutputStream class and I don't know what to do. Is there any idea?

Answer 1

Create a ByteArrayOutputStream.

Grab its content by calling toByteArray()

ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
baos.writeTo(myOutputStream); 
baos.toByteArray();

Reference

Answer 2

If the OutputStream object supplied is not already a ByteArrayOutputStream, one can wrap it inside a delegate class that will "grab" the bytes supplied to the write() methods, e.g.

public class DrainableOutputStream extends FilterOutputStream {
  private final ByteArrayOutputStream buffer;
  public DrainableOutputStream(OutputStream out) {
    super(out);
    this.buffer = new ByteArrayOutputStream();
  }
  @Override
  public void write(byte b[]) throws IOException {
    this.buffer.write(b);
    super.write(b);
  }
  @Override
  public void write(byte b[], int off, int len) throws IOException {
    this.buffer.write(b, off, len);
    super.write(b, off, len);
  }
  @Override
  public void write(int b) throws IOException {
    this.buffer.write(b);    
    super.write(b);
  }
  public byte[] toByteArray() {
    return this.buffer.toByteArray();
  }
}

To reduce the overhead, the calls to super in the above class can be omitted - e.g., if only the "conversion" to a byte array is desired.

A more detailed discussion can be found in another StackOverflow question.

Answer 3

You need to do 2 things

• Using ByteArrayOutputStream write to it
• Using toByteArray(), you will get the contents as byte[]

You could even extend it as mentioned here