Class XPathFactory
- Direct Known Subclasses:
JaxenXPathFactory
JDOM does not extend the core Java XPath API (javax.xml.xpath.XPath). Instead it creates a new API that is more JDOM and Java friendly leading to neater and more understandable code (in a JDOM context).
A JDOM XPathFactory instance is able to create JDOM XPathExpression instances that can be used to evaluate XPath expressions against JDOM Content.
The XPathFactory allows either default or custom XPathFactory instances to be
created. If you use the newInstance(String)
method then an
XPathFactory of that specific type will be created. If you use the
instance()
method then a default XPathFactory instance will be
returned.
Instances of XPathFactory are specified to be thread-safe. You can reuse an XPathFactory in multiple threads. Instances of XPathExpression are NOT thread-safe.
- Since:
- JDOM2
- Author:
- Rolf Lear
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionCreate a XPathExpression<Object> instance from this factory.<T> XPathExpression<T>
Create a XPathExpression<T> instance from this factory.<T> XPathExpression<T>
compile
(String expression, Filter<T> filter, Map<String, Object> variables, Collection<Namespace> namespaces) Create a XPathExpression<> instance from this factory.abstract <T> XPathExpression<T>
Create a Compiled XPathExpression<> instance from this factory.static final XPathFactory
instance()
Obtain an instance of an XPathFactory using the default mechanisms to determine what XPathFactory implementation to use.static final XPathFactory
newInstance
(String factoryclass) Create a new instance of an explicit XPathFactory.
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Constructor Details
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XPathFactory
public XPathFactory()
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Method Details
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instance
Obtain an instance of an XPathFactory using the default mechanisms to determine what XPathFactory implementation to use.The exact same XPathFactory instance will be returned from each call.
The default mechanism will inspect the system property (only once)
JDOMConstants.JDOM2_PROPERTY_XPATH_FACTORY
to determine what class should be used for the XPathFactory. If that property is not set then JDOM will use theJaxenXPathFactory
.- Returns:
- the default XPathFactory instance
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newInstance
Create a new instance of an explicit XPathFactory. A new instance of the specified XPathFactory is created each time. The target XPathFactory needs to have a no-argument default constructor.This method is a convenience mechanism only, and JDOM users are free to create a custom XPathFactory instance and use a simple:
XPathFactory fac = new MyXPathFactory(arg1, arg2, ...)
- Parameters:
factoryclass
- The name of the XPathFactory class to create.- Returns:
- An XPathFactory of the specified class.
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compile
public abstract <T> XPathExpression<T> compile(String expression, Filter<T> filter, Map<String, Object> variables, Namespace... namespaces) Create a Compiled XPathExpression<> instance from this factory. This is the only abstract method on this class. All other compile and evaluate methods prepare the data in some way to call this compile method.XPathFactory implementations override this method to implement support for the JDOM/XPath API.
A Filter is used to coerce resulting XPath data in to a suitable JDOM generic type. Note that the
Filters
class has a number of predefined, useful filters.Namespace
XPath expressions are always namespace aware, and expect to be able to resolve prefixes to namespace URIs. In XPath expressions the prefix "" always resolves to the empty Namespace URI "". A prefix in an XPath query is expected to resolve to exactly one URI. Multiple different prefixes in the expression may resolve to the same URI.This compile method ensures that these XPath/Namespace rules are followed and thus this method will throw IllegalArgumentException if:
- a namespace has the empty-string prefix but has a non-empty URI.
- more than one Namespace has any one prefix.
Variables
Variables are referenced from XPath expressions using a
$varname
syntax. The variable name may be a Namespace qualified variable name of the form$pfx:localname
. Variables$pa:var
and$pb:var
are the identical variables if the namespace URI for prefix 'pa' is the same URI as for prefix 'pb'.This compile method expects all variable names to be expressed in a prefix-qualified format, where all prefixes have to be available in one of the specified Namespace instances.
e.g. if you specify a variable name "ns:var" with value "value", you also need to have some namespace provided with the prefix "ns" such as
Namespace.getNamespace("ns", "http://example.com/nsuri");
Some XPath libraries allow null variable values (Jaxen), some do not (native Java). This compile method will silently convert any null Variable value to an empty string
""
.Variables are provided in the form of a Map where the key is the variable name and the mapped value is the variable value. If the entire map is null then the compile Method assumes there are no variables.
In light of the above, this compile method will throw an IllegalArgumentException if:
- a variable name is not a valid XML QName.
- The prefix associated with a variable name is not available as a Namespace.
- Type Parameters:
T
- The generic type of the results that the XPathExpression will produce.- Parameters:
expression
- The XPath expression.filter
- The Filter that is used to coerce the XPath result data in to the generic-typed results. Note that theFilters
class has a number of predefined, useful filters.variables
- Any variable values that may be referenced from the query. A null value indicates that there are no variables.namespaces
- Any namespaces that may be referenced from the query- Returns:
- an XPathExpression<> instance.
- Throws:
NullPointerException
- if the query, filter, any namespace, any variable name or any variable value is null (although the entire variables value may be null).IllegalArgumentException
- if any two Namespace values share the same prefix, or if there is any other reason that the XPath query cannot be compiled.- See Also:
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compile
public <T> XPathExpression<T> compile(String expression, Filter<T> filter, Map<String, Object> variables, Collection<Namespace> namespaces) Create a XPathExpression<> instance from this factory.- Type Parameters:
T
- The generic type of the results that the XPathExpression will produce.- Parameters:
expression
- The XPath expression.filter
- The Filter that is used to coerce the xpath result data in to the generic-typed results. Note that theFilters
class has a number of predefined, useful filters.variables
- Any variable values that may be referenced from the query. A null value indicates that there are no variables.namespaces
- List of all namespaces that may be referenced from the query- Returns:
- an XPathExpression<T> instance.
- Throws:
NullPointerException
- if the query, filter, namespaces, any variable name or any variable value is null (although the entire variables value may be null).IllegalArgumentException
- if any two Namespace values share the same prefix, or if there is any other reason that the XPath query cannot be compiled.
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compile
Create a XPathExpression<T> instance from this factory.- Type Parameters:
T
- The generic type of the results that the XPathExpression will produce.- Parameters:
expression
- The XPath expression.filter
- The Filter that is used to coerce the xpath result data in to the generic-typed results. Note that theFilters
class has a number of predefined, useful filters.- Returns:
- an XPathExpression<T> instance.
- Throws:
NullPointerException
- if the query or filter is nullIllegalArgumentException
- if there is any reason that the XPath query cannot be compiled.
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compile
Create a XPathExpression<Object> instance from this factory.- Parameters:
expression
- The XPath expression.- Returns:
- an XPathExpression<Object> instance.
- Throws:
NullPointerException
- if the query or filter is nullIllegalArgumentException
- if there is any reason that the XPath query cannot be compiled.
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