The use of Java for parallel programming on clusters relies on the need of efficient communication middleware and high-speed cluster interconnect support. Nevertheless, currently there are no solutions that fully fulfill these issues. In this paper, a Java sockets library has been tailored to increase the efficiency of Java parallel applications on clusters. This library supports high-speed cluster interconnects and its API has been extended to meet the requirements of a high performance Java RMI implementation and Java parallel applications on clusters. Thus, it provides Java with a more efficient communication middleware on clusters. The performance evaluation of this middleware on a Gigabit Ethernet (GbE) and a Scalable Coherent Interface (SCI) cluster has shown experimental evidence of throughput increase. Moreover, qualitative aspects of the solution such as transparency to the user, interoperability with other systems and no need of source code modifications are decisive to boost the performance of existing Java parallel applications and their developments in high performance Java cluster computing.