public class XPathExpressionEngine extends Object implements ExpressionEngine
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 powerful 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:
Some examples for valid keys that can be passed into the configuration's
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.
"/tables table/fields/field@type"
This is similar to the last example, but in this case a complex path ending with an attribute is defined.
Note: This extended syntax for adding properties only works
with the addProperty() method. setProperty() does not support
creating new nodes this way.
From version 1.7 on, it is possible to use regular keys in calls to
addProperty() (i.e. keys that do not have to contain a whitespace as
delimiter). In this case the key is evaluated, and the biggest part pointing
to an existing node is determined. The remaining part is then added as new
path. As an example consider the key
"tables/table[last()]/fields/field/name"
If the key does not point to an existing node, the engine will check the
paths "tables/table[last()]/fields/field",
"tables/table[last()]/fields", "tables/table[last()]", and so
on, until a key is found which points to a node. Let's assume that the last
key listed above can be resolved in this way. Then from this key the
following key is derived: "tables/table[last()] fields/field/name" by
appending the remaining part after a whitespace. This key can now be
processed using the original algorithm. Keys of this form can also be used
with the setProperty() method. However, it is still recommended to
use the old format because it makes explicit at which position new nodes
should be added. For keys without a whitespace delimiter there may be
ambiguities.
| Constructor and Description |
|---|
XPathExpressionEngine()
Creates a new instance of
XPathExpressionEngine with default
settings. |
| Modifier and Type | Method and Description |
|---|---|
String |
attributeKey(String parentKey,
String attributeName)
Returns the key of an attribute.
|
<T> String |
canonicalKey(T node,
String parentKey,
NodeHandler<T> handler)
Determines a "canonical" key for the specified node in the
expression language supported by this implementation.
|
<T> String |
nodeKey(T node,
String parentKey,
NodeHandler<T> handler)
Returns the key for the specified node in the expression language
supported by an implementation.
|
<T> NodeAddData<T> |
prepareAdd(T root,
String key,
NodeHandler<T> handler)
Returns information needed for an add operation.
|
<T> List<QueryResult<T>> |
query(T root,
String key,
NodeHandler<T> handler)
Finds the nodes and/or attributes that are matched by the specified key.
|
public XPathExpressionEngine()
XPathExpressionEngine with default
settings.public <T> List<QueryResult<T>> query(T root, String key, NodeHandler<T> handler)
NodeHandler can be used to gather the required information from
the node object. This implementation interprets the passed in key as an XPATH
expression.query in interface ExpressionEngineT - the type of the node to be processedroot - the root node of a hierarchy of nodeskey - the key to be evaluatedhandler - the NodeHandler for accessing the nodepublic <T> String nodeKey(T node, String parentKey, NodeHandler<T> handler)
getKeys() method. This implementation creates an XPATH expression that
selects the given node (under the assumption that the passed in parent
key is valid). As the nodeKey() implementation of
DefaultExpressionEngine this method does not return indices for nodes.
So all child nodes of a given parent with the same name have the same
key.nodeKey in interface ExpressionEngineT - the type of the node to be processednode - the node, for which the key must be constructedparentKey - the key of this node's parent (can be null for
the root node)handler - the NodeHandler for accessing the nodepublic String attributeKey(String parentKey, String attributeName)
ExpressionEngineparentKey must
reference the parent node of the attribute. A concrete implementation
must concatenate this parent key with the attribute name to a valid key
for this attribute.attributeKey in interface ExpressionEngineparentKey - the key to the node owning this attributeattributeName - the name of the attribute in questionpublic <T> String canonicalKey(T node, String parentKey, NodeHandler<T> handler)
nodeKey(), but
always adds an index expression to the resulting key.canonicalKey in interface ExpressionEngineT - the type of the node to be processednode - the node, for which the key must be constructedparentKey - the key of this node's parent (can be null for
the root node)handler - the NodeHandler for accessing the nodepublic <T> NodeAddData<T> prepareAdd(T root, String key, NodeHandler<T> handler)
prepareAdd in interface ExpressionEngineT - the type of the node to be processedroot - the root nodekey - the key for the new propertyhandler - the NodeHandler for accessing the nodeCopyright © 2001–2020 The Apache Software Foundation. All rights reserved.