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## weblogic.xml.xpath
Interface XPathStreamObserver

    public interface XPathStreamObserver

Defines objects which wish to be notified when events encountered in an `XMLInputStream` match a particular xpath. When the stream's client asks for the `next()` event, it is evaluated against an xpath; if it matches, the observer is notified of the event via the `observeMatch()` just before it is returned to the client.

Instances of this class are installed in an ``XPathStreamFactory`` where they are paired with a ``StreamXPath`` for which they wish to receive match notifications.

Since `XPathSreamObservers` will receive notifications on all of the streams created by the `XPathStreamFactory` in which they are installed, it is usually necessary for them to be stateless unless it can be guaranteed that the observer will never be accessed by multiple threads or for matching against different streams.

An example of such a case may occur if a client wishes to alter the stream based on xpath matches. Although this interface does not provide facilities for altering the stream, match-based mutations of the stream can easily be performed by creating a new class which does the following:

- Extends `XMLInputStream`
- Implements `XPathStreamObserver`
- Installs itself as an observer for a given XPath on a private instance of `XPathStreamFactory`.
- Set's its parent stream to be an `XMLInputStream` created by that factory.
- Has an implementation of `observeMatch` that produces some state that is consumed by its implementation of `XMLInputStream.next()`. Typically, this might mean that `observeMatch()` writes replacement events to an intermediate event buffer which is drained by the implementation of `next()`, which will always try to return the next element from the buffer, and returns `super.next()` only if the buffer is empty.

Method Summary
`void` | `observe(XMLEvent event)` Handles notification when an XMLEvent is encountered on the stream which represents a matching node that is not an attribute or namespace node.
`void` | `observeAttribute(StartElement event, Attribute attribute)` Handles notification when an XMLEvent is encountered on the stream which contains an attribute meets the criteria with which the observer was installed in the XPathStreamFactory.
`void` | `observeNamespace(StartElement event, Attribute attribute)`

Method Detail

### observe

    void observe(XMLEvent event)

  Handles notification when an XMLEvent is encountered on the stream which represents a matching node that is not an attribute or namespace node. The latter two cases are handled by observeAttribute() and observeNamespace() as described below.

  Parameters:
    `event` - The XMLEvent which matched the XPath.

### observeAttribute

    void observeAttribute(StartElement event,
                          Attribute attribute)

  Handles notification when an XMLEvent is encountered on the stream which contains an attribute meets the criteria with which the observer was installed in the XPathStreamFactory. Note that a given XMLEvent may have more than one matching attribute - a call to this method will result from each match.

  Parameters:
    `event` - The XMLEvent which contains the attribute which matched
    `attribute` - The Attribute which matched

### observeNamespace

    void observeNamespace(StartElement event,
                          Attribute attribute)

  Parameters:
    `event` - The XMLEvent which contains the attribute which matched
    `attribute` - The Attribute which contains the matched namespace declaration which matched

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