org.apache.commons.configuration2.tree.OverrideCombiner Maven / Gradle / Ivy
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/*
* 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.tree;
/**
*
* A concrete combiner implementation that is able to construct an override combination.
*
*
* An override combination means that nodes in the first node structure take precedence over nodes in the
* second, or - in other words - nodes of the second structure are only added to the resulting structure if they do not
* occur in the first one. This is especially suitable for dealing with the properties of configurations that are
* defined in an {@code override} section of a configuration definition file (hence the name).
*
*
* This combiner will iterate over the second node hierarchy and find all nodes that are not contained in the first
* hierarchy; these are added to the result. If a node can be found in both structures, it is checked whether a
* combination (in a recursive way) can be constructed for the two, which will then be added. Per default, nodes are
* combined, which occur only once in both structures. This test is implemented in the {@code canCombine()} method.
*
*
* As is true for the {@link UnionCombiner}, for this combiner list nodes are important. The {@code addListNode()} can
* be called to declare certain nodes as list nodes. This has the effect that these nodes will never be combined.
*
*
* @since 1.3
*/
public class OverrideCombiner extends NodeCombiner {
/**
* Handles the attributes during a combination process. First all attributes of the first node are added to the result.
* Then all attributes of the second node, which are not contained in the first node, are also added.
*
* @param result the resulting node
* @param node1 the first node
* @param node2 the second node
*/
protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1, final ImmutableNode node2) {
result.addAttributes(node1.getAttributes());
node2.getAttributes().keySet().forEach(attr -> {
if (!node1.getAttributes().containsKey(attr)) {
result.addAttribute(attr, HANDLER.getAttributeValue(node2, attr));
}
});
}
/**
* Tests if a child node of the second node can be combined with the given child node of the first node. If this is the
* case, the corresponding node will be returned, otherwise null. This implementation checks whether the child
* node occurs only once in both hierarchies and is no known list node.
*
* @param node1 the first node
* @param node2 the second node
* @param child the child node (of the first node)
* @return a child of the second node, with which a combination is possible
*/
protected ImmutableNode canCombine(final ImmutableNode node1, final ImmutableNode node2, final ImmutableNode child) {
if (HANDLER.getChildrenCount(node2, child.getNodeName()) == 1 && HANDLER.getChildrenCount(node1, child.getNodeName()) == 1 && !isListNode(child)) {
return HANDLER.getChildren(node2, child.getNodeName()).get(0);
}
return null;
}
/**
* Constructs an override combination for the passed in node structures.
*
* @param node1 the first node
* @param node2 the second node
* @return the resulting combined node structure
*/
@Override
public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2) {
final ImmutableNode.Builder result = new ImmutableNode.Builder();
result.name(node1.getNodeName());
// Process nodes from the first structure, which override the second
node1.forEach(child -> {
final ImmutableNode child2 = canCombine(node1, node2, child);
result.addChild(child2 != null ? combine(child, child2) : child);
});
// Process nodes from the second structure, which are not contained
// in the first structure
node2.stream().filter(child -> HANDLER.getChildrenCount(node1, child.getNodeName()) < 1).forEach(result::addChild);
// Handle attributes and value
addAttributes(result, node1, node2);
result.value(node1.getValue() != null ? node1.getValue() : node2.getValue());
return result.create();
}
}