org.jaxen
Class BaseXPath

java.lang.Object
  extended by org.jaxen.BaseXPath
All Implemented Interfaces:
Serializable, XPath
Direct Known Subclasses:
Dom4jXPath, DOMXPath, JavaBeanXPath, JDOMXPath, XOMXPath

public class BaseXPath
extends Object
implements XPath, Serializable

Base functionality for all concrete, implementation-specific XPaths.

This class provides generic functionality for further-defined implementation-specific XPaths.

If you want to adapt the Jaxen engine so that it can traverse your own object model, then this is a good base class to derive from. Typically you only really need to provide your own Navigator implementation.

Author:
bob mcwhirter, James Strachan
See Also:
XPath for dom4j, XPath for JDOM, XPath for W3C DOM, Serialized Form

Constructor Summary
protected BaseXPath(String xpathExpr)
          Construct given an XPath expression string.
  BaseXPath(String xpathExpr, Navigator navigator)
          Construct given an XPath expression string.
 
Method Summary
 void addNamespace(String prefix, String uri)
          Add a namespace prefix-to-URI mapping for this XPath expression.
 boolean booleanValueOf(Object node)
          Retrieve a boolean-value interpretation of this XPath expression when evaluated against a given context.
protected  FunctionContext createFunctionContext()
          Create a default FunctionContext.
protected  NamespaceContext createNamespaceContext()
          Create a default NamespaceContext.
protected  VariableContext createVariableContext()
          Create a default VariableContext.
 String debug()
          Returns a string representation of the parse tree.
 Object evaluate(Object context)
          Evaluate this XPath against a given context.
protected  Context getContext(Object node)
          Create a Context wrapper for the provided implementation-specific object.
protected  ContextSupport getContextSupport()
          Retrieve the ContextSupport aggregation of NamespaceContext, FunctionContext, VariableContext, and Navigator.
 FunctionContext getFunctionContext()
          Retrieve the FunctionContext used by this XPath expression.
 NamespaceContext getNamespaceContext()
          Retrieve the NamespaceContext used by this XPath expression.
 Navigator getNavigator()
          Retrieve the XML object-model-specific Navigator for us in evaluating this XPath expression.
 Expr getRootExpr()
          Retrieve the root expression of the internal compiled form of this XPath expression.
 VariableContext getVariableContext()
          Retrieve the VariableContext used by this XPath expression.
 Number numberValueOf(Object node)
          Retrieve a number-value interpretation of this XPath expression when evaluated against a given context.
 List selectNodes(Object node)
          Select all nodes that are selected by this XPath expression.
protected  List selectNodesForContext(Context context)
          Select all nodes that match this XPath expression on the given Context object.
 Object selectSingleNode(Object node)
          Select only the first node selected by this XPath expression.
protected  Object selectSingleNodeForContext(Context context)
          Return only the first node that is selected by this XPath expression.
 void setFunctionContext(FunctionContext functionContext)
          Set a FunctionContext for use with this XPath expression.
 void setNamespaceContext(NamespaceContext namespaceContext)
          Set a NamespaceContext for use with this XPath expression.
 void setVariableContext(VariableContext variableContext)
          Set a VariableContext for use with this XPath expression.
 String stringValueOf(Object node)
          Retrieves the string-value of the result of evaluating this XPath expression when evaluated against the specified context.
 String toString()
          Return the original expression text.
 String valueOf(Object node)
          Deprecated. replaced by stringValueOf(java.lang.Object)
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

BaseXPath

protected BaseXPath(String xpathExpr)
             throws JaxenException
Construct given an XPath expression string.

Parameters:
xpathExpr - the XPath expression
Throws:
JaxenException - if there is a syntax error while parsing the expression

BaseXPath

public BaseXPath(String xpathExpr,
                 Navigator navigator)
          throws JaxenException
Construct given an XPath expression string.

Parameters:
xpathExpr - the XPath expression
navigator - the XML navigator to use
Throws:
JaxenException - if there is a syntax error while parsing the expression
Method Detail

evaluate

public Object evaluate(Object context)
                throws JaxenException
Evaluate this XPath against a given context. The context of evaluation may be any object type the navigator recognizes as a node. The return value is either a String, Double, Boolean, or List of nodes.

When using this method, one must be careful to test the class of the returned object. If the returned object is a list, then the items in this list will be the actual Document, Element, Attribute, etc. objects as defined by the concrete XML object-model implementation, directly from the context document. This method does not return copies of anything, but merely returns references to objects within the source document.

Specified by:
evaluate in interface XPath
Parameters:
context - the node, node-set or Context object for evaluation. This value can be null.
Returns:
the result of evaluating the XPath expression against the supplied context
Throws:
JaxenException - if an XPath error occurs during expression evaluation
ClassCastException - if the context is not a node

selectNodes

public List selectNodes(Object node)
                 throws JaxenException
Select all nodes that are selected by this XPath expression. If multiple nodes match, multiple nodes will be returned. Nodes will be returned in document-order, as defined by the XPath specification. If the expression selects a non-node-set (i.e. a number, boolean, or string) then a List containing just that one object is returned.

Specified by:
selectNodes in interface XPath
Parameters:
node - the node, node-set or Context object for evaluation. This value can be null.
Returns:
the node-set of all items selected by this XPath expression
Throws:
JaxenException - if an XPath error occurs during expression evaluation
See Also:
selectNodesForContext(org.jaxen.Context)

selectSingleNode

public Object selectSingleNode(Object node)
                        throws JaxenException
Select only the first node selected by this XPath expression. If multiple nodes match, only one node will be returned. The selected node will be the first selected node in document-order, as defined by the XPath specification.

Specified by:
selectSingleNode in interface XPath
Parameters:
node - the node, node-set or Context object for evaluation. This value can be null.
Returns:
the node-set of all items selected by this XPath expression
Throws:
JaxenException - if an XPath error occurs during expression evaluation
See Also:
selectNodes(java.lang.Object)

valueOf

public String valueOf(Object node)
               throws JaxenException
Deprecated. replaced by stringValueOf(java.lang.Object)

Returns the XPath string-value of the argument node.

Specified by:
valueOf in interface XPath
Parameters:
node - the node whose value to take
Returns:
the XPath string value of this node
Throws:
JaxenException - if an XPath error occurs during expression evaluation

stringValueOf

public String stringValueOf(Object node)
                     throws JaxenException
Retrieves the string-value of the result of evaluating this XPath expression when evaluated against the specified context.

The string-value of the expression is determined per the string(..) core function defined in the XPath specification. This means that an expression that selects zero nodes will return the empty string, while an expression that selects one-or-more nodes will return the string-value of the first node.

Specified by:
stringValueOf in interface XPath
Parameters:
node - the node, node-set or Context object for evaluation. This value can be null.
Returns:
the string-value of the result of evaluating this expression with the specified context node
Throws:
JaxenException - if an XPath error occurs during expression evaluation

booleanValueOf

public boolean booleanValueOf(Object node)
                       throws JaxenException
Retrieve a boolean-value interpretation of this XPath expression when evaluated against a given context.

The boolean-value of the expression is determined per the boolean(..) function defined in the XPath specification. This means that an expression that selects zero nodes will return false, while an expression that selects one or more nodes will return true.

Specified by:
booleanValueOf in interface XPath
Parameters:
node - the node, node-set or Context object for evaluation. This value can be null.
Returns:
the boolean-value of the result of evaluating this expression with the specified context node
Throws:
JaxenException - if an XPath error occurs during expression evaluation

numberValueOf

public Number numberValueOf(Object node)
                     throws JaxenException
Retrieve a number-value interpretation of this XPath expression when evaluated against a given context.

The number-value of the expression is determined per the number(..) core function as defined in the XPath specification. This means that if this expression selects multiple nodes, the number-value of the first node is returned.

Specified by:
numberValueOf in interface XPath
Parameters:
node - the node, node-set or Context object for evaluation. This value can be null.
Returns:
a Double indicating the numeric value of evaluating this expression against the specified context
Throws:
JaxenException - if an XPath error occurs during expression evaluation

addNamespace

public void addNamespace(String prefix,
                         String uri)
                  throws JaxenException
Add a namespace prefix-to-URI mapping for this XPath expression.

Namespace prefix-to-URI mappings in an XPath are independent of those used within any document. Only the mapping explicitly added to this XPath will be available for resolving the XPath expression.

This is a convenience method for adding mappings to the default NamespaceContext in place for this XPath. If you have installed a custom NamespaceContext that is not a SimpleNamespaceContext, then this method will throw a JaxenException.

Specified by:
addNamespace in interface XPath
Parameters:
prefix - the namespace prefix
uri - the namespace URI
Throws:
JaxenException - if the NamespaceContext used by this XPath is not a SimpleNamespaceContext

setNamespaceContext

public void setNamespaceContext(NamespaceContext namespaceContext)
Set a NamespaceContext for use with this XPath expression.

A NamespaceContext is responsible for translating namespace prefixes within the expression into namespace URIs.

Specified by:
setNamespaceContext in interface XPath
Parameters:
namespaceContext - the NamespaceContext to install for this expression
See Also:
NamespaceContext, NamespaceContext.translateNamespacePrefixToUri(java.lang.String)

setFunctionContext

public void setFunctionContext(FunctionContext functionContext)
Set a FunctionContext for use with this XPath expression.

A FunctionContext is responsible for resolving all function calls used within the expression.

Specified by:
setFunctionContext in interface XPath
Parameters:
functionContext - the FunctionContext to install for this expression
See Also:
FunctionContext, FunctionContext.getFunction(java.lang.String, java.lang.String, java.lang.String)

setVariableContext

public void setVariableContext(VariableContext variableContext)
Set a VariableContext for use with this XPath expression.

A VariableContext is responsible for resolving all variables referenced within the expression.

Specified by:
setVariableContext in interface XPath
Parameters:
variableContext - The VariableContext to install for this expression
See Also:
VariableContext, VariableContext.getVariableValue(java.lang.String, java.lang.String, java.lang.String)

getNamespaceContext

public NamespaceContext getNamespaceContext()
Retrieve the NamespaceContext used by this XPath expression.

A NamespaceContext is responsible for mapping prefixes used within the expression to namespace URIs.

If this XPath expression has not previously had a NamespaceContext installed, a new default NamespaceContext will be created, installed and returned.

Specified by:
getNamespaceContext in interface XPath
Returns:
the NamespaceContext used by this expression
See Also:
NamespaceContext

getFunctionContext

public FunctionContext getFunctionContext()
Retrieve the FunctionContext used by this XPath expression.

A FunctionContext is responsible for resolving all function calls used within the expression.

If this XPath expression has not previously had a FunctionContext installed, a new default FunctionContext will be created, installed and returned.

Specified by:
getFunctionContext in interface XPath
Returns:
the FunctionContext used by this expression
See Also:
FunctionContext

getVariableContext

public VariableContext getVariableContext()
Retrieve the VariableContext used by this XPath expression.

A VariableContext is responsible for resolving all variables referenced within the expression.

If this XPath expression has not previously had a VariableContext installed, a new default VariableContext will be created, installed and returned.

Specified by:
getVariableContext in interface XPath
Returns:
the VariableContext used by this expression
See Also:
VariableContext

getRootExpr

public Expr getRootExpr()
Retrieve the root expression of the internal compiled form of this XPath expression.

Internally, Jaxen maintains a form of Abstract Syntax Tree (AST) to represent the structure of the XPath expression. This is normally not required during normal consumer-grade usage of Jaxen. This method is provided for hard-core users who wish to manipulate or inspect a tree-based version of the expression.

Returns:
the root of the AST of this expression

toString

public String toString()
Return the original expression text.

Overrides:
toString in class Object
Returns:
the normalized XPath expression string

debug

public String debug()
Returns a string representation of the parse tree.

Returns:
a string representation of the parse tree.

getContext

protected Context getContext(Object node)
Create a Context wrapper for the provided implementation-specific object.

Parameters:
node - the implementation-specific object to be used as the context
Returns:
a Context wrapper around the object

getContextSupport

protected ContextSupport getContextSupport()
Retrieve the ContextSupport aggregation of NamespaceContext, FunctionContext, VariableContext, and Navigator.

Returns:
aggregate ContextSupport for this XPath expression

getNavigator

public Navigator getNavigator()
Retrieve the XML object-model-specific Navigator for us in evaluating this XPath expression.

Specified by:
getNavigator in interface XPath
Returns:
the implementation-specific Navigator

createFunctionContext

protected FunctionContext createFunctionContext()
Create a default FunctionContext.

Returns:
a default FunctionContext

createNamespaceContext

protected NamespaceContext createNamespaceContext()
Create a default NamespaceContext.

Returns:
a default NamespaceContext instance

createVariableContext

protected VariableContext createVariableContext()
Create a default VariableContext.

Returns:
a default VariableContext instance

selectNodesForContext

protected List selectNodesForContext(Context context)
                              throws JaxenException
Select all nodes that match this XPath expression on the given Context object. If multiple nodes match, multiple nodes will be returned in document-order, as defined by the XPath specification. If the expression selects a non-node-set (i.e. a number, boolean, or string) then a List containing just that one object is returned.

Parameters:
context - the Context which gets evaluated
Returns:
the node-set of all items selected by this XPath expression
Throws:
JaxenException - if an XPath error occurs during expression evaluation

selectSingleNodeForContext

protected Object selectSingleNodeForContext(Context context)
                                     throws JaxenException
Return only the first node that is selected by this XPath expression. If multiple nodes match, only one node will be returned. The selected node will be the first selected node in document-order, as defined by the XPath specification. If the XPath expression selects a double, String, or boolean, then that object is returned.

Parameters:
context - the Context against which this expression is evaluated
Returns:
the first node in document order of all nodes selected by this XPath expression
Throws:
JaxenException - if an XPath error occurs during expression evaluation
See Also:
selectNodesForContext(org.jaxen.Context)


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