Commons Digester example source code file (MethodHandler.java)

This example Commons Digester source code file (MethodHandler.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Digester tags/keywords

annotation, annotation, annotationruleprovider, class, class, digesterloadingexception, digesterloadingexception, digesterrule, fromannotationsruleset, impossible, method, method, r, reflection, supported_args

The Commons Digester MethodHandler.java source code

/* $Id: MethodHandler.java 992091 2010-09-02 19:58:12Z simonetripodi $
 *
 * 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.
 */
package org.apache.commons.digester.annotations.handlers;

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

import org.apache.commons.digester.Rule;
import org.apache.commons.digester.annotations.AnnotationRuleProvider;
import org.apache.commons.digester.annotations.CreationRule;
import org.apache.commons.digester.annotations.DigesterLoaderHandler;
import org.apache.commons.digester.annotations.DigesterLoadingException;
import org.apache.commons.digester.annotations.DigesterRule;
import org.apache.commons.digester.annotations.DigesterRuleList;
import org.apache.commons.digester.annotations.FromAnnotationsRuleSet;
import org.apache.commons.digester.annotations.utils.AnnotationUtils;

/**
 * Handler that takes care to create the
 * {@link org.apache.commons.digester.annotations.providers.SetNextRuleProvider}
 * and
 * {@link org.apache.commons.digester.annotations.providers.SetRootRuleProvider}.
 *
 * @since 2.1
 */
public final class MethodHandler implements DigesterLoaderHandler<Annotation, Method> {

    /**
     * The default args size the method has to have in order to be analyzed.
     */
    private static final int SUPPORTED_ARGS = 1;

    /**
     * {@inheritDoc}
     */
    public void handle(Annotation annotation, Method element, FromAnnotationsRuleSet ruleSet) {
        if (SUPPORTED_ARGS != element.getParameterTypes().length) {
            DigesterRule rule = annotation.annotationType().getAnnotation(DigesterRule.class);

            throw new DigesterLoadingException("Methods annotated with digester annotation rule @"
                    + rule.reflectsRule().getName()
                    + " must have just one argument");
        }

        Object explicitTypesObject = AnnotationUtils.getAnnotationValue(annotation);
        if (explicitTypesObject == null
                || !explicitTypesObject.getClass().isArray()
                || Class.class != explicitTypesObject.getClass().getComponentType()) {
            throw new DigesterLoadingException("Impossible to apply this handler, @"
                    + annotation.getClass().getName()
                    + ".value() has to be of type 'Class<?>[]'");
        }

        Class<?>[] explicitTypes = (Class[]) explicitTypesObject;
        Class<?> paramType = element.getParameterTypes()[0];

        if (explicitTypes.length > 0) {
            for (Class<?> explicitType : explicitTypes) {
                if (!paramType.isAssignableFrom(explicitType)) {
                    throw new DigesterLoadingException("Impossible to handle annotation "
                            + annotation
                            + " on method "
                            + element.toGenericString()
                            + ", "
                            + explicitType.getName()
                            + " has to be a "
                            + paramType.getName());
                }

                this.doHandle(annotation, element, explicitType, ruleSet);
            }
        } else {
            this.doHandle(annotation, element, paramType, ruleSet);
        }
    }

    private void doHandle(Annotation methodAnnotation, Method method, Class<?> type, FromAnnotationsRuleSet ruleSet) {
        if (type.isInterface()
                && Modifier.isAbstract(type.getModifiers())) {
            throw new DigesterLoadingException("Impossible to proceed analyzing "
                    + methodAnnotation
                    + ", specified type '"
                    + type.getName()
                    + "' is an interface/abstract");
        }

        for (Annotation annotation : type.getAnnotations()) {
            this.doHandle(methodAnnotation, annotation, method, type, ruleSet);
        }
    }

    @SuppressWarnings("unchecked")
    private <A extends Annotation, R extends Rule> void doHandle(A methodAnnotation,
            Annotation annotation,
            Method method,
            Class<?> type,
            FromAnnotationsRuleSet ruleSet) {
        if (annotation.annotationType().isAnnotationPresent(DigesterRule.class)
                && annotation.annotationType().isAnnotationPresent(CreationRule.class)) {
            ruleSet.addRules(type);

            DigesterRule digesterRule = methodAnnotation.annotationType().getAnnotation(DigesterRule.class);
            Class<? extends AnnotationRuleProvider providerType =
                (Class<? extends AnnotationRuleProvider) digesterRule.providedBy();
            ruleSet.addRuleProvider(AnnotationUtils.getAnnotationPattern(annotation),
                    providerType,
                    methodAnnotation,
                    method);
        } else if (annotation.annotationType().isAnnotationPresent(DigesterRuleList.class)) {
            // check if it is one of the *.List annotation
            Annotation[] annotations = AnnotationUtils.getAnnotationsArrayValue(annotation);
            if (annotations != null) {
                // if it is an annotations array, process them
                for (Annotation ptr : annotations) {
                    this.doHandle(methodAnnotation, ptr, method, type, ruleSet);
                }
            }
        }
    }

}