Java Compiler-Compiler (JavaCC) is (according to sun)
 "the most popular parser generator" for use with Java [tm]
 applications.
 .
 A parser generator is a tool that reads a grammar specification
 and converts it to a Java program that can recognize matches to
 the grammar. In addition to the parser generator itself, JavaCC
 provides other standard capabilities related to parser
 generation such as tree building (via a tool called JJTree
 included with JavaCC), actions, debugging, etc.