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In the past, I've used ANLTR for both lexer and parser, and the JFlex homepage says it can interoperate with ANTLR. I wouldn't say that ANTLR's online documentation is that great. I ended up investing in 'The Definitive ANTLR reference', which helped considerably.
Another option would be the GOLD Parser.
Unlike many of the alternatives, the GOLD parser generates the parsing tables from the grammar and places them in a binary, non-executable file. Each supported language then has an engine which reads the binary tables and parses your source file.
I've not used the Java implementation specifically, but have used the Delphi engine with fairly good results.