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Name: jb33418 Date: 02/11/2002 Within the Java platform there has been a growing trend towards marking fields, or methods, or classes as having particular characteristics that indicate they should be processed in special ways by development tools, or deployment tools, or run-time libraries. For example, the JavaBeans architecture introduced various stylistic naming patterns (such as getFoo/setFoo method names) that could be used to indicate that particular methods were used for accessing properties, for registering event handlers, etc. Similarly the Enterprise JavaBeans architecture introduced various stylistic patterns that allow methods to be marked as remote methods, home methods, etc. In addition, the EJB architecture defined significant extra information in its deployment descriptors that is used to provide information on things like the persistence relationships of fields, or the transaction properties of methods, etc. Many other areas could benefit from this work, including component architectures and testing platforms. In general, the desire to provide various kinds of auxiliary information for Java elements appears to be growing. While the existing mechanisms have been adequate for simple uses, they are becoming increasingly awkward for more complicated uses. Since there seems to be a recurrent need to be able to provide auxiliary information on Java language elements, it appears to be appropriate to define an explicit way of doing this in the Java language, to allow arbitrary attribute information to be associated with particular classes/interfaces/methods/fields. We refer to this mechanism as "Java language metadata". We believe there are several elements needed as part of this work: Definition of a Java language extension that allows metadata information to be supplied for (at least) classes, interfaces, methods, and fields. This language extension will allow metadata to be recognized by development tools. It appears likely that it will be useful to allow attribute values to be associated with given metadata attributes. The exact syntax will need to be determined by the expert group. There appear to be a number of possibilities, including (but not limited to!) using a javadoc tag "@meta" or adding a new Java language keyword "meta". Definition of a runtime delivery format for metadata and of runtime APIs so that tools and libraries can access metadata information at deployment time and at runtime. Definition of rules for the attribute namespace so as to avoid accidental collisions over the same attribute name. Details will be determined by the expert group, but it seems that a mechanism similar to the Java class naming conventions might be useful. ======================================================================
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