Dr. Dobb's Journal - December 2008 - (Page 35)

d11haas_p5db 10/13/08 7:25 AM Page 35 by Oliver Haase, Jürgen Wäsch, and Bo Zhao Core Technology A Remote Java RMI Registry A custom registry that objects can register with remotely Java’s platform independence and built-in network support make it well suited for distributed computing. One key feature in this context is Java Remote Method Invocation (RMI) technology (java.sun.com/javase/technologies/core/basic/rmi/index.jsp), which lets you use the familiar method invocation paradigm to communicate between remote Java objects. This abstraction simplifies the development process because you need not deal with communication protocols, on-the-wire data representation, and connection management. Oliver and Jürgen are computer science professors at Konstanz University of Applied Sciences and can be reached at haase@ htwg-konstanz.de and juergen .waesch@ htwg-konstanz.de, respectively. Bo recently received his master's degree in communication systems engineering from Konstanz University of Applied Sciences and can be reached at zhao.konstanz@ googlemail.com. Sun Microsystems’ Java Runtime Environment (JRE) includes the rmiregistry tool, a reference implementation of the java.rmi.registry.Registry interface. This interface contains methods that let RMI servers bind remote object references to logical names, and allows RMI clients to lookup these bindings and download the associated object references. To avoid security issues (such as malicious code rebinding existing object references), the server-side methods bind, rebind, and unbind can be invoked only locally, while the client-side methods list and lookup can be invoked remotely. Figure 1 is an overview of the standard Java RMI system architecture. The downside of this trust model, however, is that it requires the host that runs rmiregistry and the RMI server object to be externally accessible. This restriction might be acceptable for heavyweight, centrally administrated applications, but not for highly dynamic, massively distributed applications, such as peer-to-peer applications. Also, the resulting distribution model prohibits location transparency, as an RMI client that retrieves a remote reference from an rmiregistry auto- matically knows the object’s location. A further shortcoming of the rmiregistry is that all bindings are kept in main memory only, rather than stored persistently. Remote RMI Registry We have built a custom RMI registry that lets remote RMI server objects invoke bind, rebind, and unbind methods. For added robustness, the bindings in the remote RMI registry are stored persistently. Figure 2 gives an overview of the extended Java RMI system architecture using such a remote RMI registry. The driver for this architectural extension was a project on a peer-to-peer computing system that builds on Java RMI. To provide connectivity even across firewalls and network address translation (NAT) boxes, we needed a mechanism for NAT traversal that is more lightweight than HTTP tunneling. We opted for a STUNT-enhanced Java RMI extension that uses hole punching for NAT traversal. (STUNT is short for “Simple Traversal of UDP Through NATs and TCP”; see nutss.gforge.cis.cornell.edu/pub/draftguha-STUNT-00.text). For the STUNT-enhanced RMI December 2008 l www.ddj.com l Dr. Dobb’s Journal 35 http://java.sun.com/javase/technologies/core/basic/rmi/index.jsp http://nutss.gforge.cis.cornell.edu/pub/draft-guha-STUNT-00.txt http://nutss.gforge.cis.cornell.edu/pub/draft-guha-STUNT-00.txt http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - December 2008

Dr. Dobb's Journal - December 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Conversations The Man Who Sold the Sky Performance on Rails LINQ-to-SQL and T-SQL A Remote Java RMI Registry Beyond B-Trees File Descriptors and Multithreaded Programs Effective Concurrency The Agile Edge Swaine's Flames

Dr. Dobb's Journal - December 2008

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