JDK 6 Build 101 JSR 269 API Changes
By darcy on Oct 05, 2006
There haven't been any API changes in JSR 269 since build 98 and the proposed final draft; however, build 101 includes a sample annotation processor showing how the API can be used to check program structure.
The sample file is under
sample/javac/processing/src/CheckNameProcessor.javafrom the root JDK installation directory.
As the name suggests, this processor checks that the source being processed follows the naming conventions discussed in the language specification. This name checking is meant to be representative of a class of properties that could be checked for at build time by annotation processors.
A few stylistic points to note in the sample:
AbstractProcessorclass is provided to make writing annotation processors more convenient by eliminating repeated boilerplate code. Generally, the results of the
getSupportedFoomethods can be specified by applying a
@SupportedFooannotation to the class. The
@Overrideannotations help ensure the methods of the class are behaving as expected. To initialize fields for objects that will persist for life of the processor object, such as the
Filerretrieved from the
ProcessingEnvironment, assign the fields in the overridden
super.inithas been called.
- Implement functionality with a visitor, but expose the
functionality with its own entry point:
NameCheckerclass provides a
checkNamesmethod for clients to pass an element to get its names checked. While this checking is implemented using a visitor, exposing that implementation detail is not friendly to clients.
- Have a policy for future language versions:
The JSR 269 API models the current language, but the language will be
changing in some future release and annotation processors written
today could be run against new language constructs of the future. Two
basic policies are:
- Write the processor to only work with the current language version.
- Write the processor to cope with unknown future constructs.
SourceVersion.latestrather than a particular version constant and by having the visitor's
visitUnknownmethod be non-fatal if called. The
visitUnknownmethod will be called when encountering a construct newer than the platform version the visitor was written to.
For production use, the
probably needs some tweaking; leave comments detailing any changes you