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<h2>Car Example</h2>

<p>This example assumes the following class is already on your CLASSPATH:</p>

<h4>Using Xalan</h4>

<p>Here is an example of using Apache <a href="http://xml.apache.org/xalan-j/">Xalan</a> with Groovy to read an existing XML file:</p>

messages = []

def processCar(car) {
    def make = XPathAPI.eval(car, '@make').str()
    def country = XPathAPI.eval(car, 'country/text()').str()
    def type = XPathAPI.eval(car, 'record/@type').str()
    messages &lt;&lt; make + ' of ' + country + ' has a ' + type + ' record'
}

def builder     = DocumentBuilderFactory.newInstance().newDocumentBuilder()
def inputStream = new ByteArrayInputStream(XmlExamples.CAR_RECORDS.bytes)
def records     = builder.parse(inputStream).documentElement

XPathAPI.selectNodeList(records, '//car').each{ processCar(it) }

assert messages == [
    'Holden of Australia has a speed record',
    'Peel of Isle of Man has a size record',
    'Bugatti of France has a price record'
]
</pre></td></tr></table>

<h4>Using Jaxen</h4>

<p>Here is an example of using <a href="http://jaxen.org/">Jaxen</a> with Groovy to read an existing XML file:</p>

messages = []

def processCar(car) {
    def make = new DOMXPath('@make').stringValueOf(car)
    def country = new DOMXPath('country/text()').stringValueOf(car)
    def type = new DOMXPath('record/@type').stringValueOf(car)
    messages &lt;&lt; make + ' of ' + country + ' has a ' + type + ' record'
}

new DOMXPath('//car').selectNodes(records).each{ processCar(it) }

assert messages == [
    'Holden of Australia has a speed record',
    'Peel of Isle of Man has a size record',
    'Bugatti of France has a price record'
]
</pre></td></tr></table>

<p>Note: many libraries (e.g. DOM4J, JDOM, XOM) bundle or provide optional support for Jaxen. You may not need to download any additional JARs to use it.</p>

<h4>Using Java's native XPath support</h4>

<p>If you are using Java 5 and above, you don't need to use the standalone Xalan jar but instead can use the now built-in XPath facilities: </p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
import javax.xml.xpath.*

def xpath = XPathFactory.newInstance().newXPath()

def nodes = xpath.evaluate( '//car', records, XPathConstants.NODESET )
nodes.each{ 
  def make = xpath.evaluate( '@make', it )
  def country = xpath.evaluate( 'country/text()', it )
  def type = xpath.evaluate( 'record/@type', it )
  messages &lt;&lt; "$make of $country has a $type record"
}
</pre></td></tr></table>

<h2>People in Groups Example</h2>

<p>Inspired by <a href="http://stage.vambenepe.com/archives/181">this example</a>, here is how to use XPath to determine which groups include all three of <em>alan</em>, <em>paul</em> and <em>ivan</em> for this graph representing group membership.</p>

<p><img class="confluence-embedded-image" src="/download/attachments/231082395/graph.png?version=1&amp;modificationDate=1371717529834" data-image-src="/download/attachments/231082395/graph.png?version=1&amp;modificationDate=1371717529834" data-linked-resource-id="231377337" data-linked-resource-type="attachment" data-linked-resource-default-alias="graph.png" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231082395" title="null > graph.png"><br />
<span style="color: grey;">Picture source: <a class="external-link" href="http://stage.vambenepe.com/pages/graph.png" rel="nofollow">http://stage.vambenepe.com/pages/graph.png</a></span></p>

<p>First, here is the XML data capturing the group membership information:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
def xml = '''
&lt;doc>
  &lt;person name="alan">&lt;g>1&lt;/g>&lt;g>2&lt;/g>&lt;g>4&lt;/g>&lt;/person>
  &lt;person name="marc">&lt;g>1&lt;/g>&lt;g>2&lt;/g>&lt;g>3&lt;/g>&lt;/person>
  &lt;person name="paul">&lt;g>2&lt;/g>&lt;g>3&lt;/g>&lt;g>4&lt;/g>&lt;/person>
  &lt;person name="ivan">&lt;g>2&lt;/g>&lt;g>4&lt;/g>&lt;/person>
  &lt;person name="eric">&lt;g>4&lt;/g>&lt;/person>
&lt;/doc>
'''
</pre></td></tr></table>

<h4>Using Java's native XPath support</h4>

<p>Here is how to check that groups 2 and 4 are the groups in question using the built-in XPath capabilities of Java 5 and above:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
import javax.xml.parsers.DocumentBuilderFactory
import javax.xml.xpath.*

xpath = '''
  /doc/person[@name="alan"]/g
  [.=/doc/person[@name="paul"]/g]
  [.=/doc/person[@name="ivan"]/g]
'''

builder = DocumentBuilderFactory.newInstance().newDocumentBuilder()
doc     = builder.parse(new ByteArrayInputStream(xml.bytes))
expr    = XPathFactory.newInstance().newXPath().compile(xpath)
nodes   = expr.evaluate(doc, XPathConstants.NODESET)
assert  nodes.collect { node -> node.textContent } == ['2', '4']
</pre></td></tr></table>

<p>And you can refactor your XPath Expression with something like:</p>

groupsOf = { name -> "/doc/person[@name='$name']/g" }
xpath    = "${groupsOf 'alan'}[.=${groupsOf 'paul'}][.=${groupsOf 'ivan'}]"
builder  = DocumentBuilderFactory.newInstance().newDocumentBuilder()
doc      = builder.parse(new ByteArrayInputStream(xml.bytes))
expr     = XPathFactory.newInstance().newXPath().compile(xpath)
nodes    = expr.evaluate(doc, XPathConstants.NODESET)
assert   nodes.collect { node -> node.textContent } == ['2', '4']
</pre></td></tr></table>

<h4>Using GPath</h4>

<p>Of course, you can also do this without XPath by using Groovy's GPath facilities as follows:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
def root = new XmlParser().parseText(xml)
Set groups = root.person.g.collect{ it.text() }
assert groups.findAll{ group ->
  root.person.g.findAll{
    it.text() == group
  }.'..'.'@name'.containsAll(['alan', 'paul', 'ivan'])
} == ['2', '4']
</pre></td></tr></table>