Force flush on a GZIPOutputStream in java

Question

we are working on a program where we need to flush (force compress and send data) a GZIPOutputStream. The problem is, that the flush method of the GZIPOutputStream doesn't work as expected (force compress and send data), instead the Stream waits for more data for efficient data compression.

When you call finish the data is compressed and sent over the output stream but the GZIPOutputStream (not the underlying stream) will be closed so we cant write more data till we create a new GZIPOutputStream, which costs time and performance.

Hope anyone can help with this.

Best regards.

Answer 1

I haven't tried this yet, and this advice won't be useful until we have Java 7 in hand, but the documentation for GZIPOutputStream's flush() method inherited from DeflaterOutputStream relies upon the flush mode specified at construction time with the syncFlush argument (related to Deflater#SYNC_FLUSH) to decide whether to flush the pending data to be compressed. This syncFlush argument is also accepted by GZIPOutputStream at construction time.

It sounds like you want to use either Deflator#SYNC_FLUSH or maybe even Deflater#FULL_FLUSH, but, before digging down that far, first try working with the two-argument or the four-argument GZIPOutputStream constructor and pass true for the syncFlush argument. That will activate the flushing behavior you desire.