[GitHub] [poi] centic9 commented on pull request #209: Improve performance of Bitmap#setData

[GitBox <gi...@apache.org>]

centic9 commented on pull request #209:
URL: https://github.com/apache/poi/pull/209#issuecomment-788094928


   It's fine,  "new ByteArrayOutputStream(int size)" would allow to populate the stream without additional allocation, but toByteArray() performs a full array-copy again, so doing it ourselves should avoid this additional copying. 
   
   In one of my projects I use the following helper class which avoids all the manual array-positioning and copying yourself and keeps using the ByteArrayOutputStream.
   
   ```
   class NonCopyingByteArrayOutputStream extends ByteArrayOutputStream {
   	public NonCopyingByteArrayOutputStream(int size) {
   		super(size);
   	}
   
   	public synchronized byte[] toByteArrayDirect() {
   		return buf;
   	}
   }
   ```
   
   In general I find it useful to verify such changes with results "before" and "after" via some tests as sometimes the JDK applies complicated optimizations which can cause changes to actually cause a slowdown.


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