Reflections 通过扫描 classpath，索引元数据，允许在运行时查询这些元数据，也可以保存收集项目中多个模块的元数据信息。

使用 Reflections 可以查询以下元数据信息： 
1）获得某个类型的所有子类型
2）获得标记了某个注解的所有类型／成员变量，支持注解参数匹配。
3）使用正则表达式获得所有匹配的资源文件
4）获得所有特定签名（包括参数，参数注解，返回值）的方法

Reflections 依赖 Google 的 Guava 库和 Javassist 库。

Maven 项目导入

<dependency><groupId>org.reflections</groupId><artifactId>reflections</artifactId><version>0.9.10</version>
</dependency>

通常用法：

Reflections reflections = new Reflections("my.project");Set<Class<? extends SomeType>> subTypes = reflections.getSubTypesOf(SomeType.class);Set<Class<?>> annotated = reflections.getTypesAnnotatedWith(SomeAnnotation.class);

Reflections 初始化代码。

//scan urls that contain 'my.package', include inputs starting with 'my.package', use the default scanners
Reflections reflections = new Reflections("my.package");//or using ConfigurationBuilder
new Reflections(new ConfigurationBuilder().setUrls(ClasspathHelper.forPackage("my.project.prefix")).setScanners(new SubTypesScanner(), new TypeAnnotationsScanner().filterResultsBy(optionalFilter), ...),.filterInputsBy(new FilterBuilder().includePackage("my.project.prefix"))...);

以下是一些使用例子代码。

//SubTypesScanner
Set<Class<? extends Module>> modules = reflections.getSubTypesOf(com.google.inject.Module.class);

//TypeAnnotationsScanner
Set<Class<?>> singletons = reflections.getTypesAnnotatedWith(javax.inject.Singleton.class);

//ResourcesScanner
Set<String> properties = reflections.getResources(Pattern.compile(".*\\.properties"));

//MethodAnnotationsScanner
Set<Method> resources =reflections.getMethodsAnnotatedWith(javax.ws.rs.Path.class);
Set<Constructor> injectables = reflections.getConstructorsAnnotatedWith(javax.inject.Inject.class);

//FieldAnnotationsScanner
Set<Field> ids = reflections.getFieldsAnnotatedWith(javax.persistence.Id.class);

//MethodParameterScanner
Set<Method> someMethods =reflections.getMethodsMatchParams(long.class, int.class);
Set<Method> voidMethods =reflections.getMethodsReturn(void.class);
Set<Method> pathParamMethods =reflections.getMethodsWithAnyParamAnnotated(PathParam.class);

//MethodParameterNamesScanner
List<String> parameterNames = reflections.getMethodParamNames(Method.class)

//MemberUsageScanner
Set<Member> usages = reflections.getMethodUsages(Method.class)