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
{
/**
* 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
for (final ImmutableNode child : node1.getChildren())
{
final ImmutableNode child2 = canCombine(node1, node2, child);
if (child2 != null)
{
result.addChild(combine(child, child2));
}
else
{
result.addChild(child);
}
}
// Process nodes from the second structure, which are not contained
// in the first structure
for (final ImmutableNode child : node2.getChildren())
{
if (HANDLER.getChildrenCount(node1, child.getNodeName()) < 1)
{
result.addChild(child);
}
}
// Handle attributes and value
addAttributes(result, node1, node2);
result.value(node1.getValue() != null ? node1.getValue() : node2
.getValue());
return result.create();
}
/**
* 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());
for (final String attr : node2.getAttributes().keySet())
{
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;
}
}