org.jdom2.xpath.util

Class AbstractXPathCompiled<T>

java.lang.Object

org.jdom2.xpath.util.AbstractXPathCompiled<T>

Type Parameters:

T - The generic type of the returned values.

All Implemented Interfaces:

java.lang.Cloneable, XPathExpression<T>

public abstract class AbstractXPathCompiled<T>
extends java.lang.Object
implements XPathExpression<T>

A mostly-implemented XPathExpression that only needs two methods to be implemented in order to satisfy the complete API. Subclasses of this MUST correctly override the clone() method which in turn should call super.clone();

Author:

Rolf Lear

Constructor Summary

Constructors

Constructor and Description
AbstractXPathCompiled(java.lang.String query, Filter<T> filter, java.util.Map<java.lang.String,java.lang.Object> variables, Namespace[] namespaces) Construct an XPathExpression.

Method Summary

Methods

Modifier and Type	Method and Description
XPathExpression<T>	clone() Subclasses of this AbstractXPathCompile class must call super.clone() in their clone methods!
XPathDiagnostic<T>	diagnose(java.lang.Object context, boolean firstonly) Evaluate the XPath query against the supplied context, but return additional data which may be useful for diagnosing problems with XPath queries.
java.util.List<T>	evaluate(java.lang.Object context) Process the compiled XPathExpression against the specified context.
T	evaluateFirst(java.lang.Object context) Return the first value in the XPath query result set type-cast to the return type of this XPathExpression.
protected abstract java.util.List<?>	evaluateRawAll(java.lang.Object context) This is the raw expression evaluator to be implemented by the back-end XPath library.
protected abstract java.lang.Object	evaluateRawFirst(java.lang.Object context) This is the raw expression evaluator to be implemented by the back-end XPath library.
java.lang.String	getExpression() Get the XPath expression
Filter<T>	getFilter() Get the Filter<T> used to coerce the raw XPath results in to the correct Generic type.
Namespace	getNamespace(java.lang.String prefix) Get the Namespace associated with a given prefix.
Namespace[]	getNamespaces() Get the Namespaces that were used to compile this XPathExpression.
java.lang.Object	getVariable(java.lang.String qname) Get the variable value associated to the given variable qname.
java.lang.Object	getVariable(java.lang.String name, Namespace uri) Get the variable value associated to the given variable name.
protected java.util.Map<java.lang.String,java.lang.Object>	getVariables() utility method that allows descendant classes to access the variables that were set on this expression, in a format that can be used in a constructor (qname/value).
java.lang.Object	setVariable(java.lang.String name, Namespace uri, java.lang.Object value) Change the defined value for a variable to some new value.
java.lang.Object	setVariable(java.lang.String qname, java.lang.Object value) Change the defined value for a variable to some new value.
java.lang.String	toString()

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

AbstractXPathCompiled

public AbstractXPathCompiled(java.lang.String query,
                     Filter<T> filter,
                     java.util.Map<java.lang.String,java.lang.Object> variables,
                     Namespace[] namespaces)

Construct an XPathExpression.

Parameters:

query - The XPath query

filter - The coercion filter.

variables - A map of variables.

namespaces - The namespaces referenced from the query.

See Also:

for conditions which throw {@link NullPointerException} or {@link IllegalArgumentException}.

Method Detail

clone

public XPathExpression<T> clone()

Subclasses of this AbstractXPathCompile class must call super.clone() in their clone methods!

This would be a sample clone method from a subclass:

                public XPathExpression<T> clone() {
                        @SuppressWarnings("unchecked")
                        final MyXPathCompiled<T> ret = (MyXPathCompiled<T>)super.clone();
                        // change any fields that need to be cloned.
                        ....
                        return ret;
                }
 

Here's the documentation from XPathExpression.clone()

Create a new instance of this XPathExpression that duplicates this instance.

The 'cloned' instance will have the same XPath query, namespace declarations, and variables. Changing a value associated with a variable on the cloned instance will not change this instance's values, and it is safe to run the evaluate methods on the cloned copy at the same time as this copy.

Specified by:

clone in interface XPathExpression<T>

Overrides:

clone in class java.lang.Object

Returns:

a new XPathExpression instance that shares the same core details as this.

getExpression

public final java.lang.String getExpression()

Description copied from interface: XPathExpression

Get the XPath expression

Specified by:

getExpression in interface XPathExpression<T>

Returns:

the string representation of the XPath expression

getNamespace

public final Namespace getNamespace(java.lang.String prefix)

Description copied from interface: XPathExpression

Get the Namespace associated with a given prefix.

Specified by:

getNamespace in interface XPathExpression<T>

Parameters:

prefix - The prefix to select the Namespace URI for.

Returns:

the URI of the specified Namespace prefix

getNamespaces

public Namespace[] getNamespaces()

Description copied from interface: XPathExpression

Get the Namespaces that were used to compile this XPathExpression.

Specified by:

getNamespaces in interface XPathExpression<T>

Returns:

a potentially empty array of Namespaces (never null).

getVariable

public final java.lang.Object getVariable(java.lang.String name,
                           Namespace uri)

Description copied from interface: XPathExpression

Get the variable value associated to the given variable name.

Specified by:

getVariable in interface XPathExpression<T>

Parameters:

name - the variable localname to retrieve the value for.

uri - the Namespace in which the variable name was declared.

Returns:

the value associated to a Variable name.

getVariable

public java.lang.Object getVariable(java.lang.String qname)

Description copied from interface: XPathExpression

Get the variable value associated to the given variable qname.

qname must consist of an optional namespace prefix and colon, followed by a mandatory variable localname. If the prefix is not specified, then the Namespace is assumed to be the Namespace.NO_NAMESPACE. If the prefix is specified, it must match with one of the declared Namespaces for this XPathExpression

Specified by:

getVariable in interface XPathExpression<T>

Parameters:

qname - the variable qname to retrieve the value for.

Returns:

the value associated to a Variable name.

setVariable

public java.lang.Object setVariable(java.lang.String name,
                           Namespace uri,
                           java.lang.Object value)

Description copied from interface: XPathExpression

Change the defined value for a variable to some new value. You may not use this method to add new variables to the compiled XPath, you can only change existing variable values.

The value of the variable may be null. Some XPath libraries support a null value, and if the library that this expression is for does not support a null value it should be translated to something meaningful for that library, typically the empty string.

Specified by:

setVariable in interface XPathExpression<T>

Parameters:

name - The variable localname to change.

uri - the Namespace in which the variable name is declared.

value - The new value to set.

Returns:

The value of the variable prior to this change.

setVariable

public java.lang.Object setVariable(java.lang.String qname,
                           java.lang.Object value)

Description copied from interface: XPathExpression

Change the defined value for a variable to some new value. You may not use this method to add new variables to the compiled XPath, you can only change existing variable values.

The value of the variable may be null. Some XPath libraries support a null value, and if the library that this expression is for does not support a null value it should be translated to something meaningful for that library, typically the empty string.

qname must consist of an optional namespace prefix and colon, followed by a mandatory variable localname. If the prefix is not specified, then the Namespace is assumed to be the Namespace.NO_NAMESPACE. If the prefix is specified, it must match with one of the declared Namespaces for this XPathExpression

Specified by:

setVariable in interface XPathExpression<T>

Parameters:

qname - The variable qname to change.

value - The new value to set.

Returns:

The value of the variable prior to this change.

getVariables

protected java.util.Map<java.lang.String,java.lang.Object> getVariables()

utility method that allows descendant classes to access the variables that were set on this expression, in a format that can be used in a constructor (qname/value).

Returns:

the variables set on this instance.

getFilter

public final Filter<T> getFilter()

Description copied from interface: XPathExpression

Get the Filter<T> used to coerce the raw XPath results in to the correct Generic type.

Specified by:

getFilter in interface XPathExpression<T>

Returns:

the Filter<T> used to coerce the raw XPath results in to the correct Generic type.

evaluate

public java.util.List<T> evaluate(java.lang.Object context)

Description copied from interface: XPathExpression

Process the compiled XPathExpression against the specified context.

In the JDOM2 XPath API the results of the raw XPath query are processed by the attached Filter<T> instance to coerce the results in to the correct generic type for this XPathExpression. The Filter process may cause some XPath results to be removed from the final results. You may instead want to call the XPathExpression.diagnose(Object, boolean) method to have access to both the raw XPath results as well as the filtered and generically typed results.

Specified by:

evaluate in interface XPathExpression<T>

Parameters:

context - The context against which to process the query.

Returns:

a list of the XPath results.

evaluateFirst

public T evaluateFirst(java.lang.Object context)

Description copied from interface: XPathExpression

Return the first value in the XPath query result set type-cast to the return type of this XPathExpression.

The concept of the 'first' result is applied before any JDOM Filter is applied. Thus, if the underlying XPath query has some results, the first result is sent through the filter. If it matches it is returned, if it does not match, then null is returned (even if some subsequent result underlying XPath result would pass the filter).

This allows the XPath implementation to optimise the evaluateFirst method by potentially using 'short-circuit' conditions in the evaluation.

Specified by:

evaluateFirst in interface XPathExpression<T>

Parameters:

context - The context against which to evaluate the expression. This will typically be a Document, Element, or some other JDOM object.

Returns:

The first XPath result (if there is any) coerced to the generic type of this XPathExpression, or null if it cannot be coerced.

diagnose

public XPathDiagnostic<T> diagnose(java.lang.Object context,
                          boolean firstonly)

Description copied from interface: XPathExpression

Evaluate the XPath query against the supplied context, but return additional data which may be useful for diagnosing problems with XPath queries.

Specified by:

diagnose in interface XPathExpression<T>

Parameters:

context - The context against which to run the query.

firstonly - Indicate whether the XPath expression can be terminated after the first successful result value.

Returns:

an XPathDiagnostic instance.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

evaluateRawAll

protected abstract java.util.List<?> evaluateRawAll(java.lang.Object context)

This is the raw expression evaluator to be implemented by the back-end XPath library.

Parameters:

context - The context against which to evaluate the query

Returns:

A list of XPath results.

evaluateRawFirst

protected abstract java.lang.Object evaluateRawFirst(java.lang.Object context)

This is the raw expression evaluator to be implemented by the back-end XPath library. When this method is processed the implementing library is free to stop processing when the result that would be the first result is retrieved.

Only the first value in the result will be processed (if any).

Parameters:

context - The context against which to evaluate the query

Returns:

The first item in the XPath results, or null if there are no results.