public class UnionCombiner extends NodeCombiner
A specialized implementation of the NodeCombiner interface
that constructs a union from two passed in node hierarchies.
The given source hierarchies are traversed and their nodes are added to the
resulting structure. Under some circumstances two nodes can be combined
rather than adding both. This is the case if both nodes are single children
(no lists) of their parents and do not have values. The corresponding check
is implemented in the findCombineNode() method.
Sometimes it is not possible for this combiner to detect whether two nodes can be combined or not. Consider the following two node hierarchies:
Hierarchy 1:
Database
+--Tables
+--Table
+--name [users]
+--fields
+--field
| +--name [uid]
+--field
| +--name [usrname]
...
Hierarchy 2:
Database
+--Tables
+--Table
+--name [documents]
+--fields
+--field
| +--name [docid]
+--field
| +--name [docname]
...
Both hierarchies contain data about database tables. Each describes a single table. If these hierarchies are to be combined, the result should probably look like the following:
Database
+--Tables
+--Table
| +--name [users]
| +--fields
| +--field
| | +--name [uid]
| ...
+--Table
+--name [documents]
+--fields
+--field
| +--name [docid]
...
i.e. the Tables nodes should be combined, while the
Table nodes should both be added to the resulting tree. From
the combiner's point of view there is no difference between the
Tables and the Table nodes in the source trees,
so the developer has to help out and give a hint that the Table
nodes belong to a list structure. This can be done using the
addListNode() method; this method expects the name of a node,
which should be treated as a list node. So if
addListNode("Table"); was called, the combiner knows that it
must not combine the Table nodes, but add it both to the
resulting tree.
listNodes| Constructor and Description |
|---|
UnionCombiner() |
| Modifier and Type | Method and Description |
|---|---|
ConfigurationNode |
combine(ConfigurationNode node1,
ConfigurationNode node2)
Combines the given nodes to a new union node.
|
protected ConfigurationNode |
findCombineNode(ConfigurationNode node1,
ConfigurationNode node2,
ConfigurationNode child,
List<ConfigurationNode> children)
Tries to find a child node of the second source node, with which a child
of the first source node can be combined.
|
addListNode, createViewNode, getListNodes, isListNodepublic ConfigurationNode combine(ConfigurationNode node1, ConfigurationNode node2)
combine in class NodeCombinernode1 - the first source nodenode2 - the second source nodeprotected ConfigurationNode findCombineNode(ConfigurationNode node1, ConfigurationNode node2, ConfigurationNode child, List<ConfigurationNode> children)
Tries to find a child node of the second source node, with which a child of the first source node can be combined. During combining of the source nodes an iteration over the first source node's children is performed. For each child node it is checked whether a corresponding child node in the second source node exists. If this is the case, these corresponding child nodes are recursively combined and the result is added to the combined node. This method implements the checks whether such a recursive combination is possible. The actual implementation tests the following conditions:
addListNode() method.If all of these tests are successful, the matching child node of the second source node is returned. Otherwise the result is null.
node1 - the first source nodenode2 - the second source nodechild - the child node of the first source node to be checkedchildren - a list with all children of the second source nodeCopyright © 2001–2013 The Apache Software Foundation. All rights reserved.