Tools for searching annotated classes in Java

The article provides a small overview of the three tools for searching annotated classes in a java project.

@Retention(RetentionPolicy.RUNTIME) public @interface MyAnnotation {} @MyAnnotation public class Bar {} @MyAnnotation public class Foo {} 

Spring

In Spring, ClassPathScanningCandidateComponentProvider serves for this purpose.

Feature: climbs into ClassPath, looking for classes that meet specified conditions

Example

 @Benchmark public void spring() { ClassPathScanningCandidateComponentProvider scanner = new ClassPathScanningCandidateComponentProvider(false); scanner.addIncludeFilter(new AnnotationTypeFilter(MyAnnotation.class)); List<String> collect = scanner .findCandidateComponents("edu.pqdn.scanner") .stream() .map(BeanDefinition::getBeanClassName) .filter(Objects::nonNull) .collect(Collectors.toList()); assertEquals(collect.size(), 2); assertTrue(collect.contains("edu.pqdn.scanner.test.Bar")); assertTrue(collect.contains("edu.pqdn.scanner.test.Foo")); } 

Reflections

Feature: climbs into ClassPath, looking for classes that meet specified conditions

 <dependency> <groupId>org.reflections</groupId> <artifactId>reflections</artifactId> <version>0.9.11</version> </dependency> 

Example

 @Benchmark public void reflection() { Reflections reflections = new Reflections("edu.pqdn.scanner"); Set<Class<?>> set = reflections.getTypesAnnotatedWith(MyAnnotation.class); List<String> collect = set.stream() .map(Class::getCanonicalName) .collect(Collectors.toList()); assertEquals(collect.size(), 2); assertTrue(collect.contains("edu.pqdn.scanner.test.Bar")); assertTrue(collect.contains("edu.pqdn.scanner.test.Foo")); } 

classindex

Feature: Does not climb in ClassPath, instead of this classes are indexed at the compilation stage

 <dependency> <groupId>org.atteo.classindex</groupId> <artifactId>classindex</artifactId> <version>3.4</version> </dependency> 

 @IndexMyAnnotated public @interface IndexerAnnotation {} @IndexerMyAnnotation public class Bar {} @IndexerMyAnnotation public class Foo {} 

Example

 @Benchmark public void indexer() { Iterable<Class<?>> iterable = ClassIndex.getAnnotated(IndexerMyAnnotation.class); List<String> list = StreamSupport.stream(iterable.spliterator(), false) .map(aClass -> aClass.getCanonicalName()) .collect(Collectors.toList()); assertEquals(list.size(), 2); assertTrue(list.contains("edu.pqdn.scanner.classindexer.test.Bar")); assertTrue(list.contains("edu.pqdn.scanner.classindexer.test.Foo")); } 

Jmh

 Benchmark Mode Cnt Score Error Units ScannerBenchmark.indexer avgt 50 0,100 ? 0,001 ms/op ScannerBenchmark.reflection avgt 50 5,157 ? 0,047 ms/op ScannerBenchmark.spring avgt 50 4,706 ? 0,294 ms/op 

Conclusion

As you can see, the indexer is the most productive tool, however, the annotations for which the search is performed must have the stereotype @IndexAnnotated.

The other two tools are working much slower, but for their work no shamanism with code is needed. The disadvantage is completely leveled out if the search is needed only at the start of the application.