Import an XML File into a Document Object Model

You can import an XML file into a Document Object Model (DOM) document node by using a matlab.io.xml.dom.Parser object or the xmlread function.

The matlab.io.xml.dom.Parser class belongs to the MATLAB® API for XML Processing (MAXP). When you use a MAXP Parser object to read an XML file, the resulting DOM document node is represented as a matlab.io.xml.dom.Document object. For a list of the classes that you can use to work with a Document object, see matlab.io.xml.dom. You do not need Java® software to use MAXP classes.

To work with a DOM document node object created by xmlread, you must use the Java API for XML Processing (JAXP). For a list of the JAXP methods and properties, see the org.w3c.dom package description at https://docs.oracle.com/javase/7/docs/api.

The XML Document Object Model

In a Document Object Model, every item in an XML file corresponds to a node. The properties and methods that you use to create and access nodes, follow standards set by the World Wide Web consortium.

For example, consider this sample XML file:

<productinfo>

<!-- This is a sample info.xml file. -->

<list>

<listitem>
<label color="blue">Import Wizard</label>
<callback>uiimport</callback>
<icon>ApplicationIcon.GENERIC_GUI</icon>
</listitem>

<listitem>
<label color="red">Profiler</label>
<callback>profile viewer</callback>
<icon>ApplicationIcon.PROFILER</icon>
</listitem>

</list>
</productinfo>

The information in the file maps to the following types of DOM nodes:

  • Element nodes — Correspond to tag names. In the info.xml file, these tags correspond to element nodes:

    • productinfo

    • list

    • listitem

    • label

    • callback

    • icon

    In this case, the list element is the parent of listitem element child nodes. The productinfo element is the root element node.

  • Text nodes — Contain values associated with element nodes. Every text node is the child of an element node. For example, the Import Wizard text node is the child of the first label element node.

  • Attribute nodes — Contain name and value pairs associated with an element node. For example, in the first label element node, color is the name of an attribute and blue is its value. Attribute nodes are not parents or children of any nodes.

  • Comment nodes — Include additional text in the file, in the form <!--Sample comment-->.

  • Document nodes — Correspond to the entire file. Use methods on the document node to create new element, text, attribute, or comment nodes.

Read an XML File Using the MAXP Parser

This example uses a matlab.io.xml.dom.Parser object to read an info.xml file into a matlab.io.xml.dom.Document node. The file contains several listitem elements. Each listitem element contains a label and callback element. The example uses MAXP methods to find the text content of the callback element that corresponds to the label that has text content Plot Tools.

Read the file into a Document object.

infoFile = fullfile(matlabroot,'toolbox/matlab/general/info.xml');
infoLabel = 'Plot Tools';
infoCbk = '';
itemFound = false;

import matlab.io.xml.dom.*
xDoc = parseFile(Parser,infoFile);

Find all the listitem elements by calling the getElementsByTagName method, which returns a matlab.io.xml.dom.NodeList object.

allListItems = getElementsByTagName(xDoc,'listitem');

For each listitem element, compare the text of the label element to Plot Tools. When you locate the correct label, get the callback text. To access an element in the NodeList object, use the node method, which uses one-based indexing. Alternatively, you can use the item method, which uses zero-based indexing.

length = allListItems.Length;
for i=1:length

    thisListItem = node(allListItems,i);
    childNode = getFirstChild(thisListItem);

    while ~isempty(childNode)
        %Filter out text, comments, and processing instructions.

        if isa(childNode,'matlab.io.xml.dom.Element')
            %Assume that each element has a single Text child
            
            childText = getData(getFirstChild(childNode));

            switch getTagName(childNode)
                case 'label'
                    itemFound = strcmp(childText,infoLabel);
                case 'callback'
                    infoCbk = childText;
            end
        end
        childNode = getNextSibling(childNode);
    end
    if itemFound
        break
    else
        infoCbk = '';
    end
end

Display the result.

fprintf('Item "%s" has a callback of "%s".\n', infoLabel,infoCbk);
Item "Plot Tools" has a callback of "figure; plottools".

Read an XML File Using xmlread

This example uses xmlread to read the info.xml file into a DOM document node and Java API for XML Processing methods to find the text content of the callback element that corresponds to the label that has text content Plot Tools.

infoFile = fullfile(matlabroot,'toolbox/matlab/general/info.xml');
infoLabel = 'Plot Tools';
infoCbk = '';
itemFound = false;

xDoc = xmlread(infoFile);

allListItems = getElementsByTagName(xDoc,'listitem');

%The item list index is zero-based.
length = allListItems.getLength-1;
for i=0:length

    thisListItem = item(allListItems,i);
    childNode = getFirstChild(thisListItem);

    while ~isempty(childNode)
        %Filter out text, comments, and processing instructions.

        if childNode.getNodeType == childNode.ELEMENT_NODE
            %Assume that each element has a single org.w3c.dom.Text child

            childText = char(childNode.getFirstChild.getData);

            switch char(childNode.getTagName)
                case 'label'
                    itemFound = strcmp(childText,infoLabel);
                case 'callback'
                    infoCbk = childText;
            end
        end
        childNode = getNextSibling(childNode);
    end
    if itemFound
        break
    else
        infoCbk = '';
    end
end
fprintf('Item "%s" has a callback of "%s".\n', infoLabel,infoCbk);
Item "Plot Tools" has a callback of "figure; plottools".

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