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JSefa (Java Simple exchange format api) is a simple library for stream-based serialization of java objects to XML, CSV, FLR or any other format and back again using an iterator-style interface independent of the serialization format. The mapping between java object types and types of the serialization format (e. g. xml complex element types) can be defined either by annotating the java classes or programmatically using a simple API. The current implementation supports XML, CSV and FLR - for XML it is based on JSR 173.

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/*
 * Copyright 2007 the original author or authors.
 *
 * Licensed 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.
 */

package net.sf.jsefa.common.annotation;

import java.lang.annotation.Annotation;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;

import net.sf.jsefa.common.util.ReflectionUtil;

/**
 * Provider for values of annotation parameters. It provides a simple solution to the following drawbacks of
 * annotations: 

 * 1) Annotations can not extend an interface so that it is not possible to express that several annotations do
 * provide the same kind of data.

 * 2) Annotated parameter values can not be set to null.
 * 
 * 
 * @author Norman Lahme-Huetig
 * 
 */
public final class AnnotationDataProvider {

    private static final List NULL_OBJECTS = Arrays.asList(new Object[]{"", NoConverterType.class,
            NoValidatorType.class, NoClass.class});

    /**
     * Returns the value of the annotation parameter with the given name of the given annotation or null if it is
     * to be interpreted as null (as the empty String, an empty array or special classes used as
     * defaults for the annotation parameter value).
     * 
     * @param  the expected type of the data to return
     * @param annotation the annotation
     * @param annotationParameterName the annotation parameter name
     * @return the annotation parameter value.
     */
    public static  T get(Annotation annotation, String annotationParameterName) {
        T result = ReflectionUtil. callMethod(annotation, annotationParameterName);
        if (NULL_OBJECTS.contains(result)) {
            return null;
        }
        if (Object[].class.isAssignableFrom(result.getClass())) {
            Object[] resultArray = (Object[]) result;
            if (resultArray.length == 0) {
                return null;
            }
        }
        return result;
    }

    /**
     * Returns the value of the annotation parameter with the given name of the annotation the given
     * annotatedElement is annotated with and which class is one of the given annotation classes. Returns null, if
     * the annotation parameter value is to be interpreted as null (as the empty String or special
     * classes used as defaults for the annotation parameter value).
     * 
     * @param  the expected type of the returned data
     * @param annotatedElement the annotated element
     * @param annotationParameterName the name of the annotation parameter
     * @param annotationClasses the annotation classes
     * @return the annotation parameter value
     */
    public static  T get(AnnotatedElement annotatedElement, String annotationParameterName,
            Class... annotationClasses) {
        for (Class annotationClass : annotationClasses) {
            if (hasParameter(annotationClass, annotationParameterName)) {
                if (annotatedElement.isAnnotationPresent(annotationClass)) {
                    return AnnotationDataProvider. get(annotatedElement.getAnnotation(annotationClass),
                            annotationParameterName);
                }
            }
        }
        return null;
    }

    /**
     * Returns true if the annotation class has an annotation parameter with the given name; false otherwise.
     * 
     * @param annotationClass the annotation class
     * @param annotationParameterName the annotation parameter name
     * @return true if the annotation class has an annotation parameter with the given name; false otherwise.
     */
    public static boolean hasParameter(Class annotationClass, String annotationParameterName) {
        Method method = ReflectionUtil.getMethod(annotationClass, annotationParameterName);
        return method != null;
    }

    private AnnotationDataProvider() {

    }

}