Design and implementation of the @Java system

Galilei, Giacomo A. (2008) Design and implementation of the @Java system. Technical Report del Dipartimento di Informatica . Università di Pisa, Pisa, IT.

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Abstract

Annotations are a recent feature introduced in languages such as Java, C#, and other languages of the .NET family, which allow programmers to attach arbitrary, structured and typed metadata to their code. These languages run on top of so-called virtual execution environments, e.g. the JVM for Java, and the CLR for .NET languages, which allow for the run-time generation of executable code. In this report we explore how annotations and the dynamic code generation capability can be used together to provide programmers with high-level methods for dynamic generation and modification of an application’s code — at run-time. The report describes the framework @Java system, the Java libraries it is constituted by, and the @Java language, which is an extension to Java allowing annotation of arbitrary statements. The strategy we developed consists in parsing a source file written using @Java language to produce a Java 5 compatible source file. Once compiled, information about annotated statements,such as their bytecode instructions, can be recovered at run-time. We developed two libraries, one that works at low level to do generic bytecode engineering called JDAsm, and one at high level called JCodeBrick.Together, these two libraries allow type-safe and totally symbolic runtime code modification and generation without any need to explicitly address bytecode instructions, letting a programmer to easily manipulate existing classes or to synthesize new ones, by inserting, deleting or extruding pieces of code. After an overview of the Annotations in Section 2, we address the @Java language and its parser in Section 3. Then a full description of the two libraries for bytecode engineering and code manipulation follows in Section 4 and 5. We introduce then in Section 6 a few motivating examples of applications of @Java, and provide a more developed case study in Section7.The last section offers conclusions and ideas for future work. The documentation of the two libraries is provided in Appendix A, completing the report.

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