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YAML 1.1 parser and emitter for Java
There is a newer version: 2.3
/**
 * Copyright (c) 2008-2012, http://www.snakeyaml.org
 *
 * 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 org.yaml.snakeyaml.representer;

import java.beans.IntrospectionException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.yaml.snakeyaml.DumperOptions.FlowStyle;
import org.yaml.snakeyaml.error.YAMLException;
import org.yaml.snakeyaml.introspector.Property;
import org.yaml.snakeyaml.nodes.MappingNode;
import org.yaml.snakeyaml.nodes.Node;
import org.yaml.snakeyaml.nodes.NodeId;
import org.yaml.snakeyaml.nodes.NodeTuple;
import org.yaml.snakeyaml.nodes.ScalarNode;
import org.yaml.snakeyaml.nodes.SequenceNode;
import org.yaml.snakeyaml.nodes.Tag;

/**
 * Represent JavaBeans
 */
public class Representer extends SafeRepresenter {

    public Representer() {
        this.representers.put(null, new RepresentJavaBean());
    }

    protected class RepresentJavaBean implements Represent {
        public Node representData(Object data) {
            try {
                return representJavaBean(getProperties(data.getClass()), data);
            } catch (IntrospectionException e) {
                throw new YAMLException(e);
            }
        }
    }

    /**
     * Tag logic:

     * - explicit root tag is set in serializer 

     * - if there is a predefined class tag it is used

     * - a global tag with class name is always used as tag. The JavaBean parent
     * of the specified JavaBean may set another tag (tag:yaml.org,2002:map)
     * when the property class is the same as runtime class
     * 
     * @param properties
     *            JavaBean getters
     * @param javaBean
     *            instance for Node
     * @return Node to get serialized
     */
    protected MappingNode representJavaBean(Set properties, Object javaBean) {
        List value = new ArrayList(properties.size());
        Tag tag;
        Tag customTag = classTags.get(javaBean.getClass());
        tag = customTag != null ? customTag : new Tag(javaBean.getClass());
        // flow style will be chosen by BaseRepresenter
        MappingNode node = new MappingNode(tag, value, null);
        representedObjects.put(javaBean, node);
        boolean bestStyle = true;
        for (Property property : properties) {
            Object memberValue = property.get(javaBean);
            Tag customPropertyTag = memberValue == null ? null : classTags.get(memberValue
                    .getClass());
            NodeTuple tuple = representJavaBeanProperty(javaBean, property, memberValue,
                    customPropertyTag);
            if (tuple == null) {
                continue;
            }
            if (((ScalarNode) tuple.getKeyNode()).getStyle() != null) {
                bestStyle = false;
            }
            Node nodeValue = tuple.getValueNode();
            if (!((nodeValue instanceof ScalarNode && ((ScalarNode) nodeValue).getStyle() == null))) {
                bestStyle = false;
            }
            value.add(tuple);
        }
        if (defaultFlowStyle != FlowStyle.AUTO) {
            node.setFlowStyle(defaultFlowStyle.getStyleBoolean());
        } else {
            node.setFlowStyle(bestStyle);
        }
        return node;
    }

    /**
     * Represent one JavaBean property.
     * 
     * @param javaBean
     *            - the instance to be represented
     * @param property
     *            - the property of the instance
     * @param propertyValue
     *            - value to be represented
     * @param customTag
     *            - user defined Tag
     * @return NodeTuple to be used in a MappingNode. Return null to skip the
     *         property
     */
    protected NodeTuple representJavaBeanProperty(Object javaBean, Property property,
            Object propertyValue, Tag customTag) {
        ScalarNode nodeKey = (ScalarNode) representData(property.getName());
        // the first occurrence of the node must keep the tag
        boolean hasAlias = this.representedObjects.containsKey(propertyValue);

        Node nodeValue = representData(propertyValue);

        if (propertyValue != null && !hasAlias) {
            NodeId nodeId = nodeValue.getNodeId();
            if (customTag == null) {
                if (nodeId == NodeId.scalar) {
                    if (propertyValue instanceof Enum) {
                        nodeValue.setTag(Tag.STR);
                    }
                } else {
                    if (nodeId == NodeId.mapping) {
                        if (property.getType() == propertyValue.getClass()) {
                            if (!(propertyValue instanceof Map)) {
                                if (!nodeValue.getTag().equals(Tag.SET)) {
                                    nodeValue.setTag(Tag.MAP);
                                }
                            }
                        }
                    }
                    checkGlobalTag(property, nodeValue, propertyValue);
                }
            }
        }

        return new NodeTuple(nodeKey, nodeValue);
    }

    /**
     * Remove redundant global tag for a type safe (generic) collection if it is
     * the same as defined by the JavaBean property
     * 
     * @param property
     *            - JavaBean property
     * @param node
     *            - representation of the property
     * @param object
     *            - instance represented by the node
     */
    @SuppressWarnings("unchecked")
    protected void checkGlobalTag(Property property, Node node, Object object) {
        Class[] arguments = property.getActualTypeArguments();
        if (arguments != null) {
            if (node.getNodeId() == NodeId.sequence) {
                // apply map tag where class is the same
                Class t = arguments[0];
                SequenceNode snode = (SequenceNode) node;
                Iterable