J/Link is a toolkit that integrates Mathematica and Java.

See: Description

Packages 
Package Description
com.wolfram.jlink
This is the main J/Link package, containing the classes and interfaces that programmers will use most.
com.wolfram.jlink.ui
Includes some classes useful in programs with non-trivial user intefaces.
com.wolfram.jlink.util
A couple of special utility classes: LinkSnooper, a program that displays MathLink traffic between two programs, and MathematicaTask, an Ant task for using Mathematica in Ant build files.

J/Link is Copyright (c) 1999-2012, Wolfram Research, Inc. All rights reserved.