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java.lang.Object org.apache.commons.configuration.tree.xpath.XPathExpressionEngine
public class XPathExpressionEngine
A specialized implementation of the ExpressionEngine
interface
that is able to evaluate XPATH expressions.
This class makes use of Commons JXPath for handling XPath expressions and mapping them to the nodes of a hierarchical configuration. This makes the rich and powerfull XPATH syntax available for accessing properties from a configuration object.
For selecting properties arbitrary XPATH expressions can be used, which
select single or multiple configuration nodes. The associated
Configuration
instance will directly pass the specified
property keys into this engine. If a key is not syntactically correct, an
exception will be thrown.
For adding new properties, this expression engine uses a specific syntax: the "key" of a new property must consist of two parts that are separated by whitespace:
addProperty()
method follow:
"/tables/table[1] type"
This will add a new type
node as a child of the first
table
element.
"/tables/table[1] @type"
Similar to the example above, but this time a new attribute named
type
will be added to the first table
element.
"/tables table/fields/field/name"
This example shows how a complex path can be added. Parent node is the
tables
element. Here a new branch consisting of the nodes
table
, fields
, field
, and
name
will be added.
Field Summary | |
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(package private) static String |
ATTR_DELIMITER
Constant for the attribute delimiter. |
(package private) static String |
PATH_DELIMITER
Constant for the path delimiter. |
Constructor Summary | |
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XPathExpressionEngine()
|
Method Summary | |
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protected org.apache.commons.jxpath.JXPathContext |
createContext(ConfigurationNode root,
String key)
Creates the JXPathContext used for executing a query. |
protected void |
initNodeAddData(NodeAddData data,
String path)
Initializes most properties of a NodeAddData object. |
String |
nodeKey(ConfigurationNode node,
String parentKey)
Returns a (canonic) key for the given node based on the parent's key. |
NodeAddData |
prepareAdd(ConfigurationNode root,
String key)
Prepares an add operation for a configuration property. |
List |
query(ConfigurationNode root,
String key)
Executes a query. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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static final String PATH_DELIMITER
static final String ATTR_DELIMITER
Constructor Detail |
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public XPathExpressionEngine()
Method Detail |
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public List query(ConfigurationNode root, String key)
query
in interface ExpressionEngine
root
- the configuration root nodekey
- the query to be executed
public String nodeKey(ConfigurationNode node, String parentKey)
nodeKey()
implementation of
DefaultExpressionEngine
this method will not return indices for nodes. So all child nodes of a
given parent whith the same name will have the same key.
nodeKey
in interface ExpressionEngine
node
- the node for which a key is to be constructedparentKey
- the key of the parent node
public NodeAddData prepareAdd(ConfigurationNode root, String key)
prepareAdd
in interface ExpressionEngine
root
- the configuration's root nodekey
- the key describing the target of the add operation and the
path of the new node
protected org.apache.commons.jxpath.JXPathContext createContext(ConfigurationNode root, String key)
JXPathContext
used for executing a query. This
method will create a new context and ensure that it is correctly
initialized.
root
- the configuration root nodekey
- the key to be queried
protected void initNodeAddData(NodeAddData data, String path)
NodeAddData
object. This
method is called by prepareAdd()
after the parent node has
been found. Its task is to interprete the passed in path of the new node.
data
- the data object to initializepath
- the path of the new node
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