Question

I have a CipherOutputStream backed by another OutputStream. After I have finished writing all the data I need encrypted to the CipherOutputStream, I need to append some unencrypted data.

The documentation for CipherOutputStream says that calling flush() will not force the final block out of the encryptor; for that I need to call close(). But close() also closes the underlying OutputStream, which I still need to write more to.

How can I force the last block out of the encryptor without closing the stream? Do I need to write my own NonClosingCipherOutputStream?

Answer 1

If you don’t have a reference to the Cipher, you could pass a FilterOutputStream to the method that creates the CipherOutputStream. In the FilterOutputStream, override the close method so that it doesn’t actually close the stream.