public class AnnotationHelper {

    private static final AnnotationHelper helper = new AnnotationHelper();
    
    protected AnnotationHelper() {
        
    }
    
    public static AnnotationHelper getInstance() {
        return helper;
    }
    
    /**
     * 得到类上面的注解信息
     * @param scannerClass
     * @param allowInjectClass
     * @return
     */
    public Annotation getClassAnnotation(Class<?> scannerClass , Class<? extends Annotation> allowInjectClass) {
        
        if(!scannerClass.isAnnotationPresent(allowInjectClass)) {
            return null;
        }
        
        return scannerClass.getAnnotation(allowInjectClass);
    }
    
    /**
     * 等到方法级别注解的信息
     * @param scannerClass：需要被扫描的class文件
     * @param allowInjectClass：注解的文件
     * @return
     */
    public List<Annotation> getMethodAnnotation(Class<?> scannerClass , Class<? extends Annotation> allowInjectClass) {
        List<Annotation> annotations = new ArrayList<Annotation>();
        
        for(Method method : scannerClass.getDeclaredMethods()) {
            if(!method.isAnnotationPresent(allowInjectClass)) {
                continue;
            }
            
            annotations.add(method.getAnnotation(allowInjectClass));
        }
        
        return annotations;
    }
    
    /**
     * 使用Java反射得到注解的信息
     * @param annotation
     * @param methodName
     * @return
     * @throws NoSuchMethodException
     * @throws SecurityException
     * @throws IllegalAccessException
     * @throws IllegalArgumentException
     * @throws InvocationTargetException
     */
    public Object getAnnotationInfo(Annotation annotation , String methodName) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        if(annotation == null) {
            return null;
        }
        
        Method method = annotation.getClass().getDeclaredMethod(methodName, null);
        return method.invoke(annotation, null);
    }
}