org.apache.xpath

## Class CachedXPathAPI

- java.lang.Object
- - org.apache.xpath.CachedXPathAPI

-     public class CachedXPathAPI
      extends java.lang.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

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `CachedXPathAPI()` Default constructor.
    `CachedXPathAPI(CachedXPathAPI priorXPathAPI)` This constructor shares its `XPathContext` with a pre-existing `CachedXPathAPI`.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `XObject` | `eval(Node contextNode, java.lang.String str)` Evaluate XPath string to an XObject.
    `XObject` | `eval(Node contextNode, java.lang.String str, Node namespaceNode)` Evaluate XPath string to an XObject.
    `XObject` | `eval(Node contextNode, java.lang.String str, PrefixResolver prefixResolver)` Evaluate XPath string to an XObject.
    `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.
    `NodeIterator` | `selectNodeIterator(Node contextNode, java.lang.String str)` Use an XPath string to select a nodelist.
    `NodeIterator` | `selectNodeIterator(Node contextNode, java.lang.String str, Node namespaceNode)` Use an XPath string to select a nodelist.
    `NodeList` | `selectNodeList(Node contextNode, java.lang.String str)` Use an XPath string to select a nodelist.
    `NodeList` | `selectNodeList(Node contextNode, java.lang.String str, Node namespaceNode)` Use an XPath string to select a nodelist.
    `Node` | `selectSingleNode(Node contextNode, java.lang.String str)` Use an XPath string to select a single node.
    `Node` | `selectSingleNode(Node contextNode, java.lang.String str, Node namespaceNode)` Use an XPath string to select a single node.

    - ### Methods inherited from class java.lang.Object

      `equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### 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 Detail

    - #### 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,
                              java.lang.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,
                              java.lang.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,
                                        java.lang.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,
                                        java.lang.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,
                                java.lang.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,
                                java.lang.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,
                     java.lang.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,
                     java.lang.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,
                     java.lang.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`

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