Java Reflection Annotation getAnnotationValue(Object obj, Class annotation, String field)

Description

Retrieve the value of the annotation

License

Apache License

Parameter

Parameter	Description
obj	target object
annotation	target annotation
field	annotation field

Exception

Parameter	Description
NoSuchMethodException	an exception
InvocationTargetException	an exception
IllegalAccessException	an exception
IllegalArgumentException	an exception

Return

value (null if object not annotated)

Declaration

public static Object getAnnotationValue(Object obj, Class<? extends Annotation> annotation, String field)
        throws IllegalArgumentException, IllegalAccessException, InvocationTargetException,
        NoSuchMethodException 

Method Source Code

//package com.java2s;
/**/*from   w  w w .  j  av  a  2s  .c o m*/
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Main {
    /**
     * Retrieve the value of the annotation
     * 
     * @param obj target object
     * @param annotation target annotation
     * @param field annotation field
     * @return value (null if object not annotated)
     * @throws NoSuchMethodException
     * @throws InvocationTargetException
     * @throws IllegalAccessException
     * @throws IllegalArgumentException
     */
    public static Object getAnnotationValue(Object obj, Class<? extends Annotation> annotation, String field)
            throws IllegalArgumentException, IllegalAccessException, InvocationTargetException,
            NoSuchMethodException {
        Class<?> cls = getClass(obj);
        if (cls.isAnnotationPresent(annotation))
            return invokeMethod(cls.getAnnotation(annotation), field);
        else
            return null;
    }

    /**
     * Get the actual class
     * 
     * @param obj target object
     * @return actual class
     */
    public static Class<?> getClass(Object obj) {
        Class<?> cls = obj.getClass();
        while (isProxied(cls)) {
            cls = cls.getSuperclass();
        }
        return cls;
    }

    /**
     * Invoke the method without parameters over the target object
     * 
     * @param obj target object
     * @param method method name
     * @return value returned by the method invocation
     * @throws IllegalArgumentException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     * @throws NoSuchMethodException
     */
    public static Object invokeMethod(Object obj, String method) throws IllegalArgumentException,
            IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        return invokeMethod(obj, method, new Object[0]);
    }

    /**
     * Invoke the method over the target object
     * 
     * @param obj target object
     * @param method method name
     * @param params parameters
     * @return value returned by the method invocation
     * @throws IllegalArgumentException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     * @throws NoSuchMethodException
     */
    public static Object invokeMethod(Object obj, String method, Object[] params) throws IllegalArgumentException,
            IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        return invokeMethod(obj, getMethod(getClass(obj), method, params), params);
    }

    /**
     * Invoke the method without parameters over the target object
     * 
     * @param obj target object
     * @param method method
     * @return value returned by the method invocation
     * @throws IllegalArgumentException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     */
    public static Object invokeMethod(Object obj, Method method)
            throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        return invokeMethod(obj, method, new Object[0]);
    }

    /**
     * Invoke the method over the target object
     * 
     * @param obj target object
     * @param method method
     * @param params parameters
     * @return value returned by the method invocation
     * @throws IllegalArgumentException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     */
    public static Object invokeMethod(Object obj, Method method, Object[] params)
            throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        return method.invoke(obj, params);
    }

    /**
     * Check is the class is proxies
     * 
     * @param cls class
     * @return proxied
     */
    public static boolean isProxied(Class<?> cls) {
        return cls.getName().contains("$$EnhancerByCGLIB$$") || cls.getName().contains("$$FastClassByCGLIB$$")
                || cls.getName().contains("_$$_javassist") || cls.getName().contains("_$$_WeldSubclass")
                || cls.getName().contains("$Proxy$");
    }

    /**
     * Get the method based on its name
     * 
     * @param cls target class
     * @param method method name
     * @param params parameters
     * @return method
     * @throws NoSuchMethodException
     */
    public static Method getMethod(Class<?> cls, String method, Object[] params) throws NoSuchMethodException {
        Class<?>[] classes = new Class[params.length];
        for (int i = 0; i < params.length; i++) {
            classes[i] = params[i].getClass();
        }
        return cls.getMethod(method, classes);
    }
}

Related

1. getAnnotationValue(Annotation annotation, String value, Class expectedType)
2. getAnnotationValue(Annotation annotation, String valueName)
3. getAnnotationValue(Class anno, Field field, String paramName)
4. getAnnotationValue(final A annotation, final Function valueRetriever, final V defaultValue)
5. getAnnotationValue(Object aObj, String aValue)
6. getAnnotationWithinHierarchy(Class fsmClass, Class aggregateClass)
7. getAnnotationWithMetaAnnotation(AnnotatedElement annotatedElement, Class metaAnnotationType)