Read Inner XML of a XML Element

Question

I was looking thru StackOverflow but i can't find best answer. I need to read XML file in JAVA. My XML file looks like below: `

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<server>
    <server01>
       <department>A1</department>
       <department>A2</department> 
    </server01>
    <server02>
       <department>A1</department>
       <department>A2</department> 
    </server02>
</server>

Is there a possiblity to read in Java elements between <server01> and <server02> , excluding rest of file? Or I need to use different tags? I found method how to read parentnodes:

NodeList serversNames = xmlD.getDocumentElement().getChildNodes();

for (int i = 0; i < serversNames.getLength(); i++) {
    Node node = serversNames.item(i);
    if (node instanceof Element) {
        Element childElement = (Element) node;
        System.out.println("tag name: " + childElement.getTagName());
    }
}

I am able to read all departments tags and save them to array:

NodeList serverName = xmlD.getElementsByTagName("department");

serversList = new String[serverName.getLength()];

System.out.println("zasieg: " + serverName.getLength());

for (int temp = 0; temp < serverName.getLength(); temp++) {
    Element shareName = null;

    shareName = (Element) serverName.item(temp);

    serversList[temp] = shareName.getTextContent();
    System.out.println(temp + " - " + serversList[temp]);
}

So, again, is there a possibility to read elements of parent node only? Elements of SERVER01 only?

Answer 1

XPath is what you want. For all intents and purposes, you can think of xpath as you would sql, only it is for xml documents instead of databases. Here is a simple example using Java (keep in mind xpath is a standard and not specific to java, so you can find many ways of doing this in pretty much any popular language):

    // Load document
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse( new FileInputStream( "/tmp/xml" ) );

    // Create XPath expression
    XPathFactory xPathfactory = XPathFactory.newInstance();
    XPath xpath = xPathfactory.newXPath();
    XPathExpression expr = xpath.compile( "//server01" );

    // Find node 'server01'
    Node node = (Node) expr.evaluate( doc, XPathConstants.NODE );
    if( node == null ) {
        System.out.println( "Node not found" );
        System.exit( 0 );
    }

    // Extract departments
    Element server01 = (Element) node;
    for( int k = 0 ; k < server01.getChildNodes().getLength() ; k++ ) {
        Node childNode = server01.getChildNodes().item( k );
        // Check if current node is a department node
        if( "department".equals( childNode.getNodeName() ) ) {
            System.out.println( childNode.getNodeName() + ": " + childNode.getTextContent().trim() );
        }
    }

Is there is a possibility to avoid this?

Yes just change XPath expression an receive only nodes you need.

// Load document
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse( new FileInputStream( "/tmp/xml" ) );

// Create XPath expression
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile( "//server01/department" );

// Find nodes 'department' under node 'server01'
NodeList node = (NodeList) expr.evaluate( doc, XPathConstants.NODESET );

// Extract departments
for( int k = 0 ; k < node.getLength() ; k++ ) {
    Node childNode = node.item( k );
    // Check if current node is a department node
    if( "department".equals( childNode.getNodeName() ) ) {
        System.out.println( "[" + k + "] " + childNode.getNodeName() + ": " + childNode.getTextContent().trim() );
    }
}

You must receive the next output:

[0] department: A1
[1] department: A2