如果XML文档中存在特定的XML元素，如何检查java

Question

I have the following question:

I would like to check, whether a XML document contains a specific XML element. Is it possible to check, for example with a java method of a specific API, which returns a boolean value, wheter a specific XML element are available in a XML document?

This is my XML document as example:

<Test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <ServiceRequest>      
     <RequestPayload>
        <LocationInformationRequest>
            <InitialInput>
                <GeoRestriction>
                    <Area>
                        <PolylinePoint>
                            <Longitude>11.0</Longitude>
                            <Latitude>12.0</Latitude>
                            <Altitude>13.0</Altitude>
                        </PolylinePoint>                            
                    </Area>
                </GeoRestriction>
            </InitialInput>
        </LocationInformationRequest>
     </RequestPayload>
  </ServiceRequest>
</Test>

I need the information as a boolean value, wheter the XML element Area are existing or not existing. The XML Document is used in my own java classes as a type of string.

Thanks for help !

Answer 1

public boolean isElementExists(String content) {
    DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
    Document inputDoc = documentBuilderFactory.newDocumentBuilder().parse(new StringReader(content));
    NodeList nodeList = inputDoc.getElementsByTagName(tagName);
    return nodeList.getlength() == 0 ? true : false;
}

Answer 2

Since the document is a string and assuming you don't need to parse it for other reasons, I would use the StAX API :

  public static boolean hasElement(String document, String localName)
      throws XMLStreamException {
    Reader reader = new StringReader(document);
    XMLStreamReader xml = XMLInputFactory.newFactory()
                                         .createXMLStreamReader(reader);
    try {
      while (xml.hasNext()) {
        if (xml.next() == XMLStreamConstants.START_ELEMENT
            && localName.equals(xml.getLocalName())) {
          return true;
        }
      }
    } finally {
      xml.close();
    }
    return false;
  }

The advantage of this API over the SAX parse is that because it is a pull parser it is possible to stop processing the document before completion without using an artificial mechanism like throwing an exception.

Answer 3

You can execute XPath queries with Javax XPath (there are other XPath API's too):

http://docs.oracle.com/javase/6/docs/api/javax/xml/xpath/package-summary.html

Answer 4

If this is all u need, u could write ur own function:

If (xmlobjectstring.contains("<Area>") and xmlobjectstring.contains("</Area>") { }

Than u just need to parse out the different objects from the xmlfile.

You could also try out the SAX-XML Reader:

http://blog.mynotiz.de/programmieren/java-sax-parser-tutorial-773/

If it gets more complicated you will need to use xpath:

http://www.ibm.com/developerworks/library/x-javaxpathapi/index.html

Answer 5

Two ways, you could try the Java Scanner class to look for a specific string (eg Longitude) assuming the existence of this word in the document implies the element exists.

Or you could define a SAXParser that uses a custom handler to go through every element in the XML file but that may be too complicated for what you want to do.