MethodHelper.java

/*
 * Copyright 2012 Guido Steinacker
 *
 * 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 de.otto.jsonhome.generator;

import org.springframework.core.LocalVariableTableParameterNameDiscoverer;
import org.springframework.core.ParameterNameDiscoverer;
import org.springframework.util.ClassUtils;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import static java.util.Arrays.asList;

/**
 * @author Guido Steinacker
 * @since 03.10.12
 */
public final class MethodHelper {

    private static final ParameterNameDiscoverer parameterNameDiscoverer = new LocalVariableTableParameterNameDiscoverer();
    public static final Annotation[][] EMPTY_ANNOTATIONS = new Annotation[1][];
    static {
        EMPTY_ANNOTATIONS[0] = new Annotation[0];
    }

    /**
     * Discovers parameter infos of a Method.
     *
     * Debug information must not be removed from the class files, otherwise the name of the method parameters can
     * not be resolved.
     *
     * @param method the Method
     * @return list of ParameterInfo in the correct ordering.
     */
    public static List<ParameterInfo> getParameterInfos(final Method method) {
        final Class<?>[] parameterTypes = method.getParameterTypes();
        final Annotation[][] parameterAnnotations = parameterAnnotationsOf(method);
        final String[] parameterNames = parameterNamesOf(method);
        final List<ParameterInfo> parameterInfos = new ArrayList<ParameterInfo>();
        for (int i=0,n=parameterNames.length; i<n; ++i) {
            parameterInfos.add(new ParameterInfo(
                    parameterNames[i],
                    parameterTypes[i],
                    parameterAnnotations.length > i
                            ? asList(parameterAnnotations[i])
                            : Collections.<Annotation>emptyList())
            );
        }
        return parameterInfos;
    }

    /**
     * Returns the names of the parameters of the specified method.
     *
     * @param method the Method
     * @return List of Strings, in the order parameters in the method's signature.
     */
    public static String[] parameterNamesOf(final Method method) {
        if (method != null) {
            final String[] parameterNames = parameterNameDiscoverer.getParameterNames(method);
            if (parameterNames == null) {
                return parameterNamesOf(methodFromSuperclass(method));
            } else {
                return parameterNames;
            }
        }
        return new String[0];
    }

    private static Annotation[][] parameterAnnotationsOf(final Method method) {
        if (method != null) {
            final Annotation[][] parameterAnnotations = method.getParameterAnnotations();
            if (isEmpty(parameterAnnotations)) {
                return parameterAnnotationsOf(methodFromSuperclass(method));
            } else {
                return parameterAnnotations;
            }
        }
        return EMPTY_ANNOTATIONS;
    }

    private static Method methodFromSuperclass(final Method method) {
        final Class<?> superclass = method.getDeclaringClass().getSuperclass();
        if (superclass != null) {
            return ClassUtils.getMethodIfAvailable(superclass, method.getName(), method.getParameterTypes());
        }
        return null;
    }

    private static boolean isEmpty(Annotation[][] parameterAnnotations) {
        for (Annotation[] parameterAnnotation : parameterAnnotations) {
            if (parameterAnnotation.length != 0) {
                return false;
            }
        }
        return true;
    }

}