ANTLR

Today i worked with some text character parsing. In our project, they have used ANTLR parser. ANTLR, ANother Tool for Language Recognition, is a language tool that provides a framework for constructing recognizers, interpreters, compilers, and translators from grammatical descriptions containing actions in a variety of target languages. ANTLR provides excellent support for tree construction, tree walking, translation, error recovery, and error reporting.

http://www.antlr.org/

We have used both Class LLkParser and Class Parser.Alos one important interface that provides is Interface AST in antlr.collections.

http://www.antlr2.org/javadoc/antlr/LLkParser.html
http://www.antlr2.org/javadoc/antlr/Parser.html#LA(int)
http://www.antlr2.org/javadoc/antlr/collections/AST.html