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XML parsing in Java

Posted on 2014-01-12
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Last Modified: 2014-01-14
How to parse XML below in Java using DOM Parser:
<employees>
  <employee id="111">
    <firstName>Rakesh</firstName>
    <lastName>Mishra</lastName>
    <location>Bangalore</location>
  </employee>
  <employee id="112">
    <firstName>John</firstName>
    <lastName>Davis</lastName>
    <location>Chennai</location>
  </employee>
  <employee id="113">
    <firstName>Rajesh</firstName>
    <lastName>Sharma</lastName>
    <location>Pune</location>
  </employee>
</employees>
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Question by:vakils
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6 Comments
 
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Expert Comment

by:mccarl
ID: 39775815
Where is this XML coming from? A file, a database, the web, or hardcoded in your Java program?  Assuming that this may be in a file, parsing is as simple as this...

DocumentBuilder documentBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();

Document doc = documentBuilder.parse(new FileInputStream("my_xml_file.xml"));

// Do something useful with "doc"

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Author Comment

by:vakils
ID: 39778527
XML comes from file. Reading nodes value, is what I want. XML elements have no attributes at this stage and some elements may not any have value. For example while traversing XML tree, if an element has no value, I get null pointer exception in element.getTextContent(). Is there a elegant way to know that element has no value, rather than checking if element is null?

XML:
<contracts>
            <contract>123</contract> // OK
             <contract_year></contract_year>        //exception
</contracts>
//Iterating through the nodes and extracting the data.
    NodeList nodeList = document.getDocumentElement().getChildNodes();

    for (int i = 0; i < nodeList.getLength(); i++) {

      //We have encountered an <employee> tag.
      Node node = nodeList.item(i);
      if (node instanceof Element) {
        Employee emp = new Employee();
        emp.id = node.getAttributes().
            getNamedItem("id").getNodeValue();

        NodeList childNodes = node.getChildNodes();
        for (int j = 0; j < childNodes.getLength(); j++) {
          Node cNode = childNodes.item(j);

          //Identifying the child tag of employee encountered.
          if (cNode instanceof Element) {
          String content = cNode.getLastChild().getTextContent().trim();  // null pointer exception if element has no value
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Author Comment

by:vakils
ID: 39778530
XML:
<employee>
            <Name>SAM</Name> // OK
             <Middle></Middle>        //exception
</employee>
//Iterating through the nodes and extracting the data.
    NodeList nodeList = document.getDocumentElement().getChildNodes();

    for (int i = 0; i < nodeList.getLength(); i++) {

      //We have encountered an <employee> tag.
      Node node = nodeList.item(i);
      if (node instanceof Element) {
        Employee emp = new Employee();
        emp.id = node.getAttributes().
            getNamedItem("id").getNodeValue();

        NodeList childNodes = node.getChildNodes();
        for (int j = 0; j < childNodes.getLength(); j++) {
          Node cNode = childNodes.item(j);

          //Identifying the child tag of employee encountered.
          if (cNode instanceof Element) {
         String content = cNode.getLastChild().getTextContent().trim();  // null pointer exception if element has no value
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Accepted Solution

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mccarl earned 500 total points
ID: 39780987
Just remove the    .getLastChild()    call from your bold line of code, ie.
String content = cNode.getTextContent().trim();

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It was the .getLastChild() method call that is returning a NULL for the empty element and so when you attempt to call  .getTextContent() on a NULL object you get the NullPointerException. Also, I'm pretty sure that .getTextContent() never returns a NULL (at least for Element nodes which are the only ones that you are processing) so calling .trim() on that should be safe.
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Author Comment

by:vakils
ID: 39781067
OK. Got it. Calling trim is OK. getLastChild is not needed.
Thanks!
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Expert Comment

by:mccarl
ID: 39781073
Not a problem, glad to help! :)
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