src/main/java/org/apache/commons/configuration2/beanutils/XMLBeanDeclaration.java

/*
 * 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.configuration2.beanutils;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;

import org.apache.commons.configuration2.BaseHierarchicalConfiguration;
import org.apache.commons.configuration2.HierarchicalConfiguration;
import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
import org.apache.commons.configuration2.tree.NodeHandler;
import org.apache.commons.lang3.StringUtils;

/**
 * <p>
 * An implementation of the {@code BeanDeclaration} interface that is suitable for XML configuration files.
 * </p>
 * <p>
 * This class defines the standard layout of a bean declaration in an XML configuration file. Such a declaration must
 * look like the following example fragment:
 * </p>
 *
 * <pre>
 *   ...
 *   &lt;personBean config-class=&quot;my.model.PersonBean&quot;
 *       lastName=&quot;Doe&quot; firstName=&quot;John&quot;&gt;
 *       &lt;config-constrarg config-value=&quot;ID03493&quot; config-type=&quot;java.lang.String&quot;/&gt;
 *       &lt;address config-class=&quot;my.model.AddressBean&quot;
 *           street=&quot;21st street 11&quot; zip=&quot;1234&quot;
 *           city=&quot;TestCity&quot;/&gt;
 *   &lt;/personBean&gt;
 * </pre>
 *
 * <p>
 * The bean declaration can be contained in an arbitrary element. Here it is the {@code personBean} element. In the
 * attributes of this element there can occur some reserved attributes, which have the following meaning:
 * </p>
 * <dl>
 * <dt>{@code config-class}</dt>
 * <dd>Here the full qualified name of the bean's class can be specified. An instance of this class will be created. If
 * this attribute is not specified, the bean class must be provided in another way, e.g. as the {@code defaultClass}
 * passed to the {@code BeanHelper} class.</dd>
 * <dt>{@code config-factory}</dt>
 * <dd>This attribute can contain the name of the {@link BeanFactory} that should be used for creating the bean. If it
 * is defined, a factory with this name must have been registered at the {@code BeanHelper} class. If this attribute is
 * missing, the default bean factory will be used.</dd>
 * <dt>{@code config-factoryParam}</dt>
 * <dd>With this attribute a parameter can be specified that will be passed to the bean factory. This may be useful for
 * custom bean factories.</dd>
 * </dl>
 * <p>
 * All further attributes starting with the {@code config-} prefix are considered as meta data and will be ignored. All
 * other attributes are treated as properties of the bean to be created, i.e. corresponding setter methods of the bean
 * will be invoked with the values specified here.
 * </p>
 * <p>
 * If the bean to be created has also some complex properties (which are itself beans), their values cannot be
 * initialized from attributes. For this purpose nested elements can be used. The example listing shows how an address
 * bean can be initialized. This is done in a nested element whose name must match the name of a property of the
 * enclosing bean declaration. The format of this nested element is exactly the same as for the bean declaration itself,
 * i.e. it can have attributes defining meta data or bean properties and even further nested elements for complex bean
 * properties.
 * </p>
 * <p>
 * If the bean should be created using a specific constructor, the constructor arguments have to be specified. This is
 * done by an arbitrary number of nested {@code <config-constrarg>} elements. Each element can either have the
 * {@code config-value} attribute - then it defines a simple value - or must be again a bean declaration (conforming to
 * the format defined here) defining the complex value of this constructor argument.
 * </p>
 * <p>
 * A {@code XMLBeanDeclaration} object is usually created from a {@code HierarchicalConfiguration}. From this it will
 * derive a {@code SubnodeConfiguration}, which is used to access the needed properties. This subnode configuration can
 * be obtained using the {@link #getConfiguration()} method. All of its properties can be accessed in the usual way. To
 * ensure that the property keys used by this class are understood by the configuration, the default expression engine
 * will be set.
 * </p>
 *
 * @since 1.3
 */
public class XMLBeanDeclaration implements BeanDeclaration {

    /**
     * An internal helper class which wraps the node with the bean declaration and the corresponding node handler.
     *
     * @param <T> the type of the node
     */
    static class NodeData<T> {

        /** The wrapped node. */
        private final T node;

        /** The node handler for interacting with this node. */
        private final NodeHandler<T> nodeHandler;

        /**
         * Constructs a new instance of {@code NodeData}.
         *
         * @param node the node
         * @param nodeHandler the node handler
         */
        NodeData(final T node, final NodeHandler<T> nodeHandler) {
            this.node = node;
            this.nodeHandler = nodeHandler;
        }

        /**
         * Returns the unescaped name of the node stored in this data object. This method handles the case that the node name
         * may contain reserved characters with a special meaning for the current expression engine. In this case, the
         * characters affected have to be escaped accordingly.
         *
         * @param config the configuration
         * @return the escaped node name
         */
        String escapedNodeName(final HierarchicalConfiguration<?> config) {
            return config.getExpressionEngine().nodeKey(node, StringUtils.EMPTY, nodeHandler);
        }

        /**
         * Gets the value of the attribute with the given name of the wrapped node.
         *
         * @param key the key of the attribute
         * @return the value of this attribute
         */
        Object getAttribute(final String key) {
            return nodeHandler.getAttributeValue(node, key);
        }

        /**
         * Gets a set with the names of the attributes of the wrapped node.
         *
         * @return the attribute names of this node
         */
        Set<String> getAttributes() {
            return nodeHandler.getAttributes(node);
        }

        /**
         * Gets a list with the children of the wrapped node, again wrapped into {@code NodeData} objects.
         *
         * @return a list with the children
         */
        List<NodeData<T>> getChildren() {
            return wrapInNodeData(nodeHandler.getChildren(node));
        }

        /**
         * Gets a list with the children of the wrapped node with the given name, again wrapped into {@code NodeData}
         * objects.
         *
         * @param name the name of the desired child nodes
         * @return a list with the children with this name
         */
        List<NodeData<T>> getChildren(final String name) {
            return wrapInNodeData(nodeHandler.getChildren(node, name));
        }

        /**
         * Returns a flag whether the wrapped node is the root node of the passed in configuration.
         *
         * @param config the configuration
         * @return a flag whether this node is the configuration's root node
         */
        boolean matchesConfigRootNode(final HierarchicalConfiguration<?> config) {
            return config.getNodeModel().getNodeHandler().getRootNode().equals(node);
        }

        /**
         * Returns the name of the wrapped node.
         *
         * @return the node name
         */
        String nodeName() {
            return nodeHandler.nodeName(node);
        }

        /**
         * Wraps the passed in list of nodes in {@code NodeData} objects.
         *
         * @param nodes the list with nodes
         * @return the wrapped nodes
         */
        List<NodeData<T>> wrapInNodeData(final List<T> nodes) {
            return nodes.stream().map(n -> new NodeData<>(n, nodeHandler)).collect(Collectors.toList());
        }
    }

    /** Constant for the prefix of reserved attributes. */
    public static final String RESERVED_PREFIX = "config-";

    /** Constant for the prefix for reserved attributes. */
    public static final String ATTR_PREFIX = "[@" + RESERVED_PREFIX;

    /** Constant for the bean class attribute. */
    public static final String ATTR_BEAN_CLASS = ATTR_PREFIX + "class]";

    /** Constant for the bean factory attribute. */
    public static final String ATTR_BEAN_FACTORY = ATTR_PREFIX + "factory]";

    /** Constant for the bean factory parameter attribute. */
    public static final String ATTR_FACTORY_PARAM = ATTR_PREFIX + "factoryParam]";

    /** Constant for the name of the bean class attribute. */
    private static final String ATTR_BEAN_CLASS_NAME = RESERVED_PREFIX + "class";

    /** Constant for the name of the element for constructor arguments. */
    private static final String ELEM_CTOR_ARG = RESERVED_PREFIX + "constrarg";

    /**
     * Constant for the name of the attribute with the value of a constructor argument.
     */
    private static final String ATTR_CTOR_VALUE = RESERVED_PREFIX + "value";

    /**
     * Constant for the name of the attribute with the data type of a constructor argument.
     */
    private static final String ATTR_CTOR_TYPE = RESERVED_PREFIX + "type";

    /**
     * Creates a {@code NodeData} object from the root node of the given configuration.
     *
     * @param config the configuration
     * @param <T> the type of the nodes
     * @return the {@code NodeData} object
     */
    private static <T> NodeData<T> createNodeDataFromConfiguration(final HierarchicalConfiguration<T> config) {
        final NodeHandler<T> handler = config.getNodeModel().getNodeHandler();
        return new NodeData<>(handler.getRootNode(), handler);
    }

    /**
     * Tests whether the constructor argument represented by the given configuration node is a bean declaration.
     *
     * @param nodeData the configuration node in question
     * @return a flag whether this constructor argument is a bean declaration
     */
    private static boolean isBeanDeclarationArgument(final NodeData<?> nodeData) {
        return !nodeData.getAttributes().contains(ATTR_BEAN_CLASS_NAME);
    }

    /** Stores the associated configuration. */
    private final HierarchicalConfiguration<?> configuration;

    /** Stores the configuration node that contains the bean declaration. */
    private final NodeData<?> nodeData;

    /** The name of the default bean class. */
    private final String defaultBeanClassName;

    /**
     * Constructs a new instance of {@code XMLBeanDeclaration} and initializes it with the configuration node that contains the
     * bean declaration. This constructor is used internally.
     *
     * @param config the configuration
     * @param node the node with the bean declaration.
     */
    XMLBeanDeclaration(final HierarchicalConfiguration<?> config, final NodeData<?> node) {
        this.nodeData = node;
        configuration = config;
        defaultBeanClassName = null;
        initSubnodeConfiguration(config);
    }

    /**
     * Constructs a new instance of {@code XMLBeanDeclaration} and initializes it from the given configuration. The
     * configuration's root node must contain the bean declaration.
     *
     * @param config the configuration with the bean declaration
     * @param <T> the node type of the configuration
     */
    public <T> XMLBeanDeclaration(final HierarchicalConfiguration<T> config) {
        this(config, (String) null);
    }

    /**
     * Constructs a new instance of {@code XMLBeanDeclaration} and initializes it from the given configuration. The passed in
     * key points to the bean declaration.
     *
     * @param config the configuration (must not be <b>null</b>)
     * @param key the key to the bean declaration (this key must point to exactly one bean declaration or a
     *        {@code IllegalArgumentException} exception will be thrown)
     * @param <T> the node type of the configuration
     * @throws IllegalArgumentException if required information is missing to construct the bean declaration
     */
    public <T> XMLBeanDeclaration(final HierarchicalConfiguration<T> config, final String key) {
        this(config, key, false);
    }

    /**
     * Constructs a new instance of {@code XMLBeanDeclaration} and initializes it from the given configuration supporting
     * optional declarations.
     *
     * @param config the configuration (must not be <b>null</b>)
     * @param key the key to the bean declaration
     * @param optional a flag whether this declaration is optional; if set to <b>true</b>, no exception will be thrown if
     *        the passed in key is undefined
     * @param <T> the node type of the configuration
     * @throws IllegalArgumentException if required information is missing to construct the bean declaration
     */
    public <T> XMLBeanDeclaration(final HierarchicalConfiguration<T> config, final String key, final boolean optional) {
        this(config, key, optional, null);
    }

    /**
     * Constructs a new instance of {@code XMLBeanDeclaration} and initializes it from the given configuration supporting
     * optional declarations and a default bean class name. The passed in key points to the bean declaration. If the key
     * does not exist and the boolean argument is <b>true</b>, the declaration is initialized with an empty configuration.
     * It is possible to create objects from such an empty declaration if a default class is provided. If the key on the
     * other hand has multiple values or is undefined and the boolean argument is <b>false</b>, a
     * {@code IllegalArgumentException} exception will be thrown. It is possible to set a default bean class name; this name
     * is used if the configuration does not contain a bean class.
     *
     * @param config the configuration (must not be <b>null</b>)
     * @param key the key to the bean declaration
     * @param optional a flag whether this declaration is optional; if set to <b>true</b>, no exception will be thrown if
     *        the passed in key is undefined
     * @param defBeanClsName a default bean class name
     * @param <T> the node type of the configuration
     * @throws IllegalArgumentException if required information is missing to construct the bean declaration
     * @since 2.0
     */
    public <T> XMLBeanDeclaration(final HierarchicalConfiguration<T> config, final String key, final boolean optional, final String defBeanClsName) {
        if (config == null) {
            throw new IllegalArgumentException("Configuration must not be null!");
        }

        HierarchicalConfiguration<?> tmpconfiguration;
        try {
            tmpconfiguration = config.configurationAt(key);
        } catch (final ConfigurationRuntimeException iex) {
            // If we reach this block, the key does not have exactly one value
            if (!optional || config.getMaxIndex(key) > 0) {
                throw iex;
            }
            tmpconfiguration = new BaseHierarchicalConfiguration();
        }
        this.nodeData = createNodeDataFromConfiguration(tmpconfiguration);
        this.configuration = tmpconfiguration;
        defaultBeanClassName = defBeanClsName;
        initSubnodeConfiguration(getConfiguration());
    }

    /**
     * Creates a new {@code BeanDeclaration} for a child node of the current configuration node. This method is called by
     * {@code getNestedBeanDeclarations()} for all complex sub properties detected by this method. Derived classes can hook
     * in if they need a specific initialization. This base implementation creates a {@code XMLBeanDeclaration} that is
     * properly initialized from the passed in node.
     *
     * @param nodeData the child node, for which a {@code BeanDeclaration} is to be created
     * @return the {@code BeanDeclaration} for this child node
     */
    BeanDeclaration createBeanDeclaration(final NodeData<?> nodeData) {
        for (final HierarchicalConfiguration<?> config : getConfiguration().configurationsAt(nodeData.escapedNodeName(getConfiguration()))) {
            if (nodeData.matchesConfigRootNode(config)) {
                return new XMLBeanDeclaration(config, nodeData);
            }
        }
        throw new ConfigurationRuntimeException("Unable to match node for " + nodeData.nodeName());
    }

    /**
     * Creates a {@code ConstructorArg} object for the specified configuration node.
     *
     * @param child the configuration node
     * @return the corresponding {@code ConstructorArg} object
     */
    private ConstructorArg createConstructorArg(final NodeData<?> child) {
        final String type = getAttribute(child, ATTR_CTOR_TYPE);
        if (isBeanDeclarationArgument(child)) {
            return ConstructorArg.forValue(getAttribute(child, ATTR_CTOR_VALUE), type);
        }
        return ConstructorArg.forBeanDeclaration(createBeanDeclaration(child), type);
    }

    /**
     * Gets an attribute of a configuration node. This method also takes interpolation into account.
     *
     * @param nodeData the node
     * @param attribute the name of the attribute
     * @return the string value of this attribute (can be <b>null</b>)
     */
    private String getAttribute(final NodeData<?> nodeData, final String attribute) {
        final Object value = nodeData.getAttribute(attribute);
        return value == null ? null : String.valueOf(interpolate(value));
    }

    /**
     * Gets a set with the names of the attributes of the configuration node holding the data of this bean declaration.
     *
     * @return the attribute names of the underlying configuration node
     */
    protected Set<String> getAttributeNames() {
        return getNode().getAttributes();
    }

    /**
     * Gets the name of the class of the bean to be created. This information is obtained from the {@code config-class}
     * attribute.
     *
     * @return the name of the bean's class
     */
    @Override
    public String getBeanClassName() {
        return getConfiguration().getString(ATTR_BEAN_CLASS, getDefaultBeanClassName());
    }

    /**
     * Gets the name of the bean factory. This information is fetched from the {@code config-factory} attribute.
     *
     * @return the name of the bean factory
     */
    @Override
    public String getBeanFactoryName() {
        return getConfiguration().getString(ATTR_BEAN_FACTORY, null);
    }

    /**
     * Gets a parameter for the bean factory. This information is fetched from the {@code config-factoryParam} attribute.
     *
     * @return the parameter for the bean factory
     */
    @Override
    public Object getBeanFactoryParameter() {
        return getConfiguration().getProperty(ATTR_FACTORY_PARAM);
    }

    /**
     * Gets a map with the bean's (simple) properties. The properties are collected from all attribute nodes, which are
     * not reserved.
     *
     * @return a map with the bean's properties
     */
    @Override
    public Map<String, Object> getBeanProperties() {
        return getAttributeNames().stream().filter(e -> !isReservedAttributeName(e))
            .collect(Collectors.toMap(Function.identity(), e -> interpolate(getNode().getAttribute(e))));
    }

    /**
     * Gets the configuration object this bean declaration is based on.
     *
     * @return the associated configuration
     */
    public HierarchicalConfiguration<?> getConfiguration() {
        return configuration;
    }

    /**
     * {@inheritDoc} This implementation processes all child nodes with the name {@code config-constrarg}. If such a node
     * has a {@code config-class} attribute, it is considered a nested bean declaration; otherwise it is interpreted as a
     * simple value. If no nested constructor argument declarations are found, result is an empty collection.
     */
    @Override
    public Collection<ConstructorArg> getConstructorArgs() {
        return getNode().getChildren(ELEM_CTOR_ARG).stream().map(this::createConstructorArg).collect(Collectors.toCollection(LinkedList::new));
    }

    /**
     * Gets the name of the default bean class. This class is used if no bean class is specified in the configuration. It
     * may be <b>null</b> if no default class was set.
     *
     * @return the default bean class name
     * @since 2.0
     */
    public String getDefaultBeanClassName() {
        return defaultBeanClassName;
    }

    /**
     * Gets a map with bean declarations for the complex properties of the bean to be created. These declarations are
     * obtained from the child nodes of this declaration's root node.
     *
     * @return a map with bean declarations for complex properties
     */
    @Override
    public Map<String, Object> getNestedBeanDeclarations() {
        final Map<String, Object> nested = new HashMap<>();
        getNode().getChildren().forEach(child -> {
            if (!isReservedChildName(child.nodeName())) {
                final Object obj = nested.get(child.nodeName());
                if (obj != null) {
                    final List<BeanDeclaration> list;
                    if (obj instanceof List) {
                        // Safe because we created the lists ourselves.
                        @SuppressWarnings("unchecked")
                        final List<BeanDeclaration> tmpList = (List<BeanDeclaration>) obj;
                        list = tmpList;
                    } else {
                        list = new ArrayList<>();
                        list.add((BeanDeclaration) obj);
                        nested.put(child.nodeName(), list);
                    }
                    list.add(createBeanDeclaration(child));
                } else {
                    nested.put(child.nodeName(), createBeanDeclaration(child));
                }
            }
        });
        return nested;
    }

    /**
     * Gets the data about the associated node.
     *
     * @return the node with the bean declaration
     */
    NodeData<?> getNode() {
        return nodeData;
    }

    /**
     * Initializes the internally managed sub configuration. This method will set some default values for some properties.
     *
     * @param conf the configuration to initialize
     */
    private void initSubnodeConfiguration(final HierarchicalConfiguration<?> conf) {
        conf.setExpressionEngine(null);
    }

    /**
     * Performs interpolation for the specified value. This implementation will interpolate against the current subnode
     * configuration's parent. If sub classes need a different interpolation mechanism, they should override this method.
     *
     * @param value the value that is to be interpolated
     * @return the interpolated value
     */
    protected Object interpolate(final Object value) {
        final ConfigurationInterpolator interpolator = getConfiguration().getInterpolator();
        return interpolator != null ? interpolator.interpolate(value) : value;
    }

    /**
     * Tests if the specified attribute name is reserved and thus does not point to a property of the bean to be created.
     * This method is called when processing the attributes of this bean declaration. It is then possible to ignore some
     * attributes with a specific meaning. This implementation delegates to {@link #isReservedName(String)}.
     *
     * @param name the name of the attribute to be checked
     * @return a flag whether this name is reserved
     * @since 2.0
     */
    protected boolean isReservedAttributeName(final String name) {
        return isReservedName(name);
    }

    /**
     * Tests if the specified child node name is reserved and thus should be ignored. This method is called when processing
     * child nodes of this bean declaration. It is then possible to ignore some nodes with a specific meaning. This
     * implementation delegates to {@link #isReservedName(String)} .
     *
     * @param name the name of the child node to be checked
     * @return a flag whether this name is reserved
     * @since 2.0
     */
    protected boolean isReservedChildName(final String name) {
        return isReservedName(name);
    }

    /**
     * Tests if the specified name of a node or attribute is reserved and thus should be ignored. This method is called per
     * default by the methods for checking attribute and child node names. It checks whether the passed in name starts with
     * the reserved prefix.
     *
     * @param name the name to be checked
     * @return a flag whether this name is reserved
     */
    protected boolean isReservedName(final String name) {
        return name == null || name.startsWith(RESERVED_PREFIX);
    }
}