Probably everyone has done this at some point :), but here is my take on an event/push-based SAX-like JSON parser which I needed for a library I am working on.
I needed a very fast parser working on a byte input that just provides me with events about structural JSON elements so that a consumer can implement a hierarchical model on that. The parser had to be as straight-forward and as fuzz-less as possible. No abstraction, no internal AST building, nothing.
First I tried a JavaCC-generated one, which ultimately became the bottleneck of the whole library (needless to say that the requirements also ruled out any other JSON parsing library since most of them also handle marshalling/POJO-mapping which I did not need).
So I opted for a minimal, complete handwritten solution.
I also post this in the hope that someone will probably provide an even more optimized solution. I could really use it!
All parsers developed so far can be found here: https://github.com/httpdigest/ftljson/tree/master/src/ftljson