Conclusions
As you can see, Swing includes a complete HTML parser that you can use for your own applications. I have used this parser with a number of programs that I have written, and I have found it to be very useful. It is particularly helpful for handling improperly formatted HTML, which can trip up some HTML parsers.
The biggest downside to this HTML parser is that it is not thread safe (thread safety has always been a problem with Swing components). This HTML processor is no different. I have used the Swing parser in heavily threaded environments, and it has resulted in a crasheventually. If you want to use this HTML processor in a heavily threaded environment, you need to take steps to ensure that only one thread uses it at a time.
Despite this one weakness, however, the Swing thread processor is very capable and should serve you well.