I am working on a Spring based Web application which performs Predictive Analysis based on the user historical data and come up with offers to users. I need to implement a Predictive Analysis or any regression kind of functionality which gives a confidence score/prediction to present those offers. I am a Java developer and looked at Weka, Mahout to get the desired result. But both the tools dont provide good documentation and it is highly difficult to proceed with them. I need a suggestion regarding Java based analytics API to process my data using regression or Neural Networks or Decision Trees and provides a confidence score depicting customers probablity on buying the product in future.
Any help in this regard is highly appreciable.
I'd advise you to keep trying with Weka. It's a great tool, not only for implementation but also to get an idea of which algorithms will work for you, what your data looks like, etc. The book is worth the price, but if you're not willing to buy it, this wiki page might be a good starting point.
It might be best to start with testing, not programming - I believe the quote goes "60% of the difficulty of machine learning is understanding the dataset". Play around with the Weka GUI, find out what works best for you and your data, and do try some of the meta-classifiers (boosting, bagging, stacking); they often give great results (at the cost of processing time).