Writing grid applications is hard. First, interfaces to existing grid middleware often are too low-level for application programmers who are domain experts rather than computer scientists. Second, grid APIs tend to evolve too quickly for applications to follow. Third, failures and configuration incompatibilities require applications to use different solutions to the same problem, depending on the actual sites in use. This paper describes the Java Grid Application Toolkit (Java-GAT) that provides a high-level, middleware-independent and site-independent interface to the grid. The JavaGAT uses nested exceptions and intelligent dispatching of method invocations to handle errors and to automatically select suitable grid middleware implementations for requested operations. The JavaGAT's adaptor writing framework simplifies the implementation of interfaces to new middleware releases by combining nested exceptions and intelligent dispatching with rich default functionality. The many applications and middleware adaptors that have been provided by third-party developers indicate the viability of our approach.
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