Package org.apache.xpath

Class CachedXPathAPI

java.lang.Object
org.apache.xpath.CachedXPathAPI
public class CachedXPathAPI
extends Object
The methods in this class are convenience methods into the low-level XPath API. These functions tend to be a little slow, since a number of objects must be created for each evaluation. A faster way is to precompile the XPaths using the low-level API, and then just use the XPaths over and over. This is an alternative for the old XPathAPI class, which provided static methods for the purpose but had the drawback of instantiating a new XPathContext (and thus building a new DTMManager, and new DTMs) each time it was called. XPathAPIObject instead retains its context as long as the object persists, reusing the DTMs. This does have a downside: if you've changed your source document, you should obtain a new XPathAPIObject to continue searching it, since trying to use the old DTMs will probably yield bad results or malfunction outright... and the cached DTMs may consume memory until this object and its context are returned to the heap. Essentially, it's the caller's responsibility to decide when to discard the cache.
See Also:
XPath Specification

  • Field Details

    • xpathSupport

      protected XPathContext xpathSupport
      XPathContext, and thus the document model system (DTMs), persists through multiple calls to this object. This is set in the constructor.

  • Constructor Details

    • CachedXPathAPI

      public CachedXPathAPI()

      Default constructor. Establishes its own XPathContext, and hence its own DTMManager. Good choice for simple uses.

      Note that any particular instance of CachedXPathAPI must not be operated upon by multiple threads without synchronization; we do not currently support multithreaded access to a single DTM.

    • CachedXPathAPI

      public CachedXPathAPI​(CachedXPathAPI priorXPathAPI)

      This constructor shares its XPathContext with a pre-existing CachedXPathAPI. That allows sharing document models (DTM) and previously established location state.

      Note that the original CachedXPathAPI and the new one should not be operated upon concurrently; we do not support multithreaded access to a single DTM at this time. Similarly, any particular instance of CachedXPathAPI must not be operated upon by multiple threads without synchronization.

      %REVIEW% Should this instead do a clone-and-reset on the XPathSupport object?

  • Method Details

    • getXPathContext

      public XPathContext getXPathContext()
      Returns the XPathSupport object used in this CachedXPathAPI %REVIEW% I'm somewhat concerned about the loss of encapsulation this causes, but the xml-security folks say they need it.

    • selectSingleNode

      public Node selectSingleNode​(Node contextNode, String str) throws TransformerException
      Use an XPath string to select a single node. XPath namespace prefixes are resolved from the context node, which may not be what you want (see the next method).
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      Returns:
      The first node found that matches the XPath, or null.
      Throws:
      TransformerException

    • selectSingleNode

      public Node selectSingleNode​(Node contextNode, String str, Node namespaceNode) throws TransformerException
      Use an XPath string to select a single node. XPath namespace prefixes are resolved from the namespaceNode.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      namespaceNode - The node from which prefixes in the XPath will be resolved to namespaces.
      Returns:
      The first node found that matches the XPath, or null.
      Throws:
      TransformerException

    • selectNodeIterator

      public NodeIterator selectNodeIterator​(Node contextNode, String str) throws TransformerException
      Use an XPath string to select a nodelist. XPath namespace prefixes are resolved from the contextNode.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      Returns:
      A NodeIterator, should never be null.
      Throws:
      TransformerException

    • selectNodeIterator

      public NodeIterator selectNodeIterator​(Node contextNode, String str, Node namespaceNode) throws TransformerException
      Use an XPath string to select a nodelist. XPath namespace prefixes are resolved from the namespaceNode.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      namespaceNode - The node from which prefixes in the XPath will be resolved to namespaces.
      Returns:
      A NodeIterator, should never be null.
      Throws:
      TransformerException

    • selectNodeList

      public NodeList selectNodeList​(Node contextNode, String str) throws TransformerException
      Use an XPath string to select a nodelist. XPath namespace prefixes are resolved from the contextNode.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      Returns:
      A NodeIterator, should never be null.
      Throws:
      TransformerException

    • selectNodeList

      public NodeList selectNodeList​(Node contextNode, String str, Node namespaceNode) throws TransformerException
      Use an XPath string to select a nodelist. XPath namespace prefixes are resolved from the namespaceNode.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      namespaceNode - The node from which prefixes in the XPath will be resolved to namespaces.
      Returns:
      A NodeIterator, should never be null.
      Throws:
      TransformerException

    • eval

      public XObject eval​(Node contextNode, String str) throws TransformerException
      Evaluate XPath string to an XObject. Using this method, XPath namespace prefixes will be resolved from the namespaceNode.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      Returns:
      An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
      Throws:
      TransformerException
      See Also:
      XObject, XNull, XBoolean, XNumber, XString, XRTreeFrag

    • eval

      public XObject eval​(Node contextNode, String str, Node namespaceNode) throws TransformerException
      Evaluate XPath string to an XObject. XPath namespace prefixes are resolved from the namespaceNode. The implementation of this is a little slow, since it creates a number of objects each time it is called. This could be optimized to keep the same objects around, but then thread-safety issues would arise.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      namespaceNode - The node from which prefixes in the XPath will be resolved to namespaces.
      Returns:
      An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
      Throws:
      TransformerException
      See Also:
      XObject, XNull, XBoolean, XNumber, XString, XRTreeFrag

    • eval

      public XObject eval​(Node contextNode, String str, PrefixResolver prefixResolver) throws TransformerException
      Evaluate XPath string to an XObject. XPath namespace prefixes are resolved from the namespaceNode. The implementation of this is a little slow, since it creates a number of objects each time it is called. This could be optimized to keep the same objects around, but then thread-safety issues would arise.
      Parameters:
      contextNode - The node to start searching from.
      str - A valid XPath string.
      prefixResolver - Will be called if the parser encounters namespace prefixes, to resolve the prefixes to URLs.
      Returns:
      An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
      Throws:
      TransformerException
      See Also:
      XObject, XNull, XBoolean, XNumber, XString, XRTreeFrag