Writing a delegating CharsetDecoder?

Question

I want to write a CharsetDecoder that wraps an arbitrary existing decoder. Basically I want to run a standard decoder, but do special things for all the malformed input, not just the first bad sequence.
The CharsetDecoder interface requires that I do this by implementing decodeLoop(). Unfortunately I cannot just wrap the delegate's decodeLoop(), because it's a protected method. That only leaves the two decode() methods. The problem with both is that I (inside my decodeLoop) don't know if endOfInput should be set. The single-parameter decode() method assumes it, and for the other decode() method I have to supply it. If I set it true when I'm invoked from a StreamDecoder there's a risk of spurious failures because the input buffer might only have part of a multi-byte sequence at any time, but the rest will show up later. If I use the second method and set it false there's a risk that I'll never get to process trailing malformed input, as the decode() method that invoked me will generate its own malformed result at the end of the buffer.
The crucial information is stored as the ST_END state, but my own state is hidden from me in decodeLoop().
Does anyone know how this is supposed to work? It seems like the CharsetDecoder interface got a bit carried away with OO.

Answer 1

I had a similar problem when I wanted to delegate to a Swing drag-and-drop object, which had a protected method.
You can use Reflection to get the appropriate Method from the Class of the decoder you're delegating to. Then call setAccessible(true) on the Method; after that you can call invoke() on the Method even though it's protected.