非常好用的反射框架Reflections

Reflections通过扫描classpath，索引元数据，并且允许在运行时查询这些元数据。

使用Reflections可以很轻松的获取以下元数据信息：

• 获取某个类型的全部子类
• 只要类型、构造器、方法，字段上带有特定注解，便能获取带有这个注解的全部信息（类型、构造器、方法，字段）
• 获取所有能匹配某个正则表达式的资源
• 获取所有带有特定签名的方法，包括参数，参数注解，返回类型
• 获取所有方法的名字
• 获取代码里所有字段、方法名、构造器的使用

Maven依赖

在pom.xml中添加reflections的依赖：

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

API 使用

//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"))
     ...);

扫描子类

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

扫描注解

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

扫描资源

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

扫描方法注解

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

扫描字段注解

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

扫描方法参数

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

扫描方法参数名

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

扫描方法调用情况

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

总结

项目中使用

public class ReflectionTest {
    public static void main(String[] args) {
        // 扫包
        Reflections reflections = new Reflections(new ConfigurationBuilder()
                                                  .forPackages("com.boothsun.reflections") // 指定路径URL
                                                  .addScanners(new SubTypesScanner()) // 添加子类扫描工具
                                                  .addScanners(new FieldAnnotationsScanner()) // 添加 属性注解扫描工具
                                                  .addScanners(new MethodAnnotationsScanner() ) // 添加 方法注解扫描工具
                                                  .addScanners(new MethodParameterScanner() ) // 添加方法参数扫描工具
                                                 );
        // 反射出子类
        Set<Class<? extends ISayHello>> set = reflections.getSubTypesOf( ISayHello.class ) ;
        System.out.println("getSubTypesOf:" + set);

        // 反射出带有指定注解的类
        Set<Class<?>> ss = reflections.getTypesAnnotatedWith( MyAnnotation.class );
        System.out.println("getTypesAnnotatedWith:" + ss);

        // 获取带有特定注解对应的方法
        Set<Method> methods = reflections.getMethodsAnnotatedWith( MyMethodAnnotation.class ) ;
        System.out.println("getMethodsAnnotatedWith:" + methods);

        // 获取带有特定注解对应的字段
        Set<Field> fields = reflections.getFieldsAnnotatedWith( Autowired.class ) ;
        System.out.println("getFieldsAnnotatedWith:" + fields);

        // 获取特定参数对应的方法
        Set<Method> someMethods = reflections.getMethodsMatchParams(long.class, int.class);
        System.out.println("getMethodsMatchParams:" + someMethods);

        Set<Method> voidMethods = reflections.getMethodsReturn(void.class);
        System.out.println( "getMethodsReturn:" + voidMethods);

        Set<Method> pathParamMethods =reflections.getMethodsWithAnyParamAnnotated( PathParam.class);
        System.out.println("getMethodsWithAnyParamAnnotated:" + pathParamMethods);
    }

}