close() : Closes this output stream and releases any system resources associated with this stream.
=> content is not yet sent to the client (this will be done automatically later), but you can't append anything anymore
flush() : Flushes this output stream and forces any buffered output bytes to be written out.
=> content is sent immediately to the client (does anybody knowns if it is then closed?) and any attempt to forward/include it will now throw an IllegalState Exception. I guess a subsequent write() would not generate an error, but it would not send any data to the client.
Hope this helps
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