LibRec is a promising JAVA library for Recommender Systems. It implements a lot of Recommender Algorithms. It consists of three major components: Generic Interfaces, Data Structures and Recommendation Algorithms.

Apache Mahout is a project of Apache Software Foundation. Mahout helps building scalable Machine Learning applications. It primarily focuses in the areas of Collaborative Filtering, Classification, and Clustering.
Here is a very nice video tutorial on Mahout Item Recommender Tutorial using Java and Eclipse. It thoroughly explains about how to use Movielens dataset and create an Item-based recommender system to recommend certain number of most similar items for each items.

I followed the article of installing Eclipse Web Tool Platform (WTP) from these two links:
Servlet and JSP development with Eclipse WTP
Setup Eclipse and Tomcat 7 on Linux
Now, while running my project in Eclipse, I get the following error message:

My JSP project was running fine on Eclipse. However, I got the following error when I tried to add some value to database through my project data insert form.

org.apache.jasper.JasperException: javax.servlet.ServletException: java.lang.UnsupportedClassVersionError: com/mysql/jdbc/Driver : Unsupported major.minor version 51.0

I got the following error while working on a JSP project on Eclipse IDE. I have been using Tomcat server version 7.
Here is the error message:

I have been using Tomcat server version 7. I get the following error message when I try to run the JSP application from Eclipse IDE.
Starting Tomcat v7.0 Server at localhost has encountered a problem.