Natural Language Processing engine integration

Hi Everyone, has anyone had to use an external 3rd party open source solution for sentiment analyses based on context?
I know the Big Data Sandbox has a Twitter/Sentiment Analyses example but that is based on key-word matching and sentiment weighting based on individual words. I need something that makes use of the contextual information within a sentence. Any help or useful suggestions are greatly appreciated. 
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Re: Natural Language Processing engine integration

I only know about tools related to the language R (which is Open Source). For R exists a couple of java libraries.
Another tool is the data miner (also Open Source) and can be included in Java applications (e.g. Talend ;-)