WebLogic: The Definitive Guide

WebLogic’s XPath API

WebLogic XPath API lets you match XPath expressions against an XML document, represented either as a DOM tree or an XMLInputStream. The API is contained in the weblogic.xml.xpath.* package. Though the XPath syntax and semantics follow the W3C standard, there is still no standard Java API for manipulating XPath expressions, so this is a welcome API.

Using the API with a DOM

To use the API, construct DOMXPath instances representing your XPath. Here are a few examples:

DOMXPath threeDebt = new DOMXPath("sum(//co[@type='3']/debt)");
DOMXPath haveFirst = new DOMXPath("count(//co[@type='1']) > 0");
DOMXPath biggestDebt = new DOMXPath("//co[debt > 1000]/debt");

We will use the following XML as test input:

<world>
  <co type='1'><debt>100</debt></co> 
  <co type='3'><debt>1000</debt></co> 
  <co type='3'><debt>2000</debt></co>
</world>

You can match the XPath expressions against either a DOM node or the entire document itself. Use a node if you intend to just search a portion of the document. To evaluate the XPath expression, you must invoke one of the following evaluate methods on the DOMXPath instance:

public boolean evaluateAsBoolean(Document|Node);
public java.util.Set evaluateAsNodeset(Document|Node);
public double evaluateAsNumber(Document|Node);
public String evaluateAsString(Document|Node);

The actual evaluate method you invoke will depend on the type of the expected result(s) of your XPath expression. For example, we would invoke the earlier XPath expressions as follows: ...