JIProlog - Java Internet Prolog is a cross-platform pure Java 100% Prolog interpreter which integrates Prolog and Java languages in a very easy way.
JIProlog allows to call Prolog predicates from Java without dealing with native code and allows to invoke Java methods from Prolog in the same way you call predicates.
JIProlog is designed to work with any Java 1.1 platform or later, including Java enabled application servers, Java enabled browsers, PDAs compliant with Personal Java 1.1, mobile phones compliant with MIDP 1.0/2.0 and Symbian OS mobile phones.

More info about JIProlog are available here