Example Usage

Read below for examples that show how you would use the XMLBuilder utility to create and manipulate XML documents like the following:

<?xml version="1.0" encoding="UTF-8"?>
<Projects>
    <java-xmlbuilder language="Java" scm="SVN">
        <Location type="URL">http://code.google.com/p/java-xmlbuilder/</Location>
    </java-xmlbuilder>
    <JetS3t language="Java" scm="CVS">
        <Location type="URL">http://jets3t.s3.amazonaws.com/index.html</Location>
    </JetS3t>
</Projects>

Create a New XML Document

To begin, you create a new builder and XML document by specifying the name of the document's root element. See ExampleUsage#Parse_XML if you want to start with an existing XML document.

XMLBuilder builder = XMLBuilder.create("Projects");

The XMLBuilder object returned by the create method, and by all other XML manipulation methods, provides methods that you can use to add more nodes to the document. For example, to add the java-xmlbuilder and JetS3t nodes to the root element you could do the following.

XMLBuilder e1 = builder.element("java-xmlbuilder");
XMLBuilder e2 = builder.element("JetS3t");

And to add attributes or further sub-elements to the two new elements, you could call the appropriate methods on the variables assigned to each new node like so:

e1.attribute("language", "Java");
e1.attribute("scm", "SVN");

This is straight-forward enough, but it is far more verbose than necessary because the code does not take advantage of XMLBuilder's method-chaining feature.

Method Chaining

Every XMLBuilder method that adds something to the XML document will return an XMLBuilder object that represents either a newly-added element, or the element to which something has been added. This feature means that you can chain together many method calls without the need to assign intermediate objects to variables.

With this in mind, here is code that performs the same job as the code above without any unnecessary variables.

XMLBuilder builder = XMLBuilder.create("Projects")
    .element("java-xmlbuilder")
        .attribute("language", "Java")
        .attribute("scm", "SVN")
        .element("Location")
        .up()
    .up()
    .element("JetS3t");

There are two important things to notice in the code above:

• When you add a new element to the document with the element method, the XMLBuilder node returned will represent that new element. If you invoke methods on this node, attributes and elements will be added to the new node rather than to the document's root.
• Once you have finished adding items to a new element, you can call the up() method to retrieve the XMLBuilder node that represents the parent of the current node. If you balance every call to element() with a call to up(), you can write code that closely resembles the structure of the XML document you are creating.

Shorthand Methods

To make your XML building code even shorter and easier to type, there are shorthand synonyms for every XML manipulation method. Instead of calling element() you can use the elem() or e() methods, and instead of typing attribute() you can use attr() or a().

Here is the complete code to build our example XML document using shorthand methods.

XMLBuilder builder = XMLBuilder.create("Projects")
    .e("java-xmlbuilder")
        .a("language", "Java")
        .a("scm","SVN")                    
        .e("Location")
            .a("type", "URL")
            .t("http://code.google.com/p/java-xmlbuilder/")
        .up()
    .up()
    .e("JetS3t")
        .a("language", "Java")
        .a("scm","CVS")
        .e("Location")
            .a("type", "URL")
            .t("http://jets3t.s3.amazonaws.com/index.html");

The following methods are available for adding items to the XML document:

Output

XMLBuilder includes two convenient methods for outputting a document.

You can use the toWriter method to print the document to an output stream or file:

PrintWriter writer = new PrintWriter(new FileOutputStream("projects.xml"));
builder.toWriter(writer, outputProperties);

Or you can convert the document straight to a text string:

builder.asString(outputProperties);

Both of these output methods take an outputProperties parameter that you can use to control how the output is generated. Any output properties you provide are forwarded to the underlying Transformer object that is used to serialize the XML document. You might specify any non-standard properties like so:

Properties outputProperties = new Properties();

// Explicitly identify the output as an XML document
outputProperties.put(javax.xml.transform.OutputKeys.METHOD, "xml");

// Pretty-print the XML output (doesn't work in all cases)
outputProperties.put(javax.xml.transform.OutputKeys.INDENT, "yes");

// Get 2-space indenting when using the Apache transformer
outputProperties.put("{http://xml.apache.org/xslt}indent-amount", "2");

// Omit the XML declaration header
outputProperties.put(javax.xml.transform.OutputKeys.OMIT_XML_DECLARATION, "yes");

If you do not wish to change the default properties for your output, you can provide a null value for outputProperties.

Accessing the Underlying Document

Because XMLBuilder merely acts as a layer on top of the standard JAXP XML document building tools, you can easily access the underlying Element or Document objects if you need to manipulate them in ways that XMLBuilder does not allow.

To obtain the Element represented by any given XMLBuilder node:

org.w3c.dom.Element element = xmlBuilderNode.getElement();

To obtain the entire XML document:

org.w3c.dom.Document doc = builder.getDocument();

You can also use the root() method to quickly obtain the builder object that represents the document's root element, no matter deep an element hierarchy your code has built:

org.w3c.dom.Element rootElement = 
    XMLBuilder.create("This")
        .e("Element")
            .e("Hierarchy")
                .e("Is")
                    .e("Really")
                        .e("Very")
                            .e("Deep")
                                .e("Indeed")
    .root().getElement();

Parse XML

If you already have an XML document to which you need to add nodes or attributes, you can create a new XMLBuilder instance by parsing an InputSource:

XMLBuilder builder = XMLBuilder.parse(
   new InputSource(new StringReader(YOUR_XML_DOCUMENT)));

Parsing an existing document will produce an XMLBuilder object pointing at the document's root Element node. If you add elements or attributes to this builder object, they will be added to the document's root element.

If you need to add nodes elsewhere in the parsed document, you will need to find the correct location in the document using XPath statements.

Find Nodes with XPath

To add nodes at a specific point in an XML document, you can use XPath to obtain an XMLBuilder at the correct location. The XMLBuilder#xpathFind method takes an XPath query string and returns a builder object located at the first Element that matches the query.

XMLBuilder firstLocationBuilder = builder.xpathFind("//Location");

Note that the XPath query provided to this method must resolve to at least one Element node. If the query does not match any nodes, or if the first match is anything other than an Element, the method will throw an XPathExpressionException.

Like all other XMLBuilder methods, this method can be easily chained to others when adding nodes. Here is an example that adds a second element, Location2, inside the JetS3t element of our example document.

builder.xpathFind("//JetS3t").elem("Location2").attr("type", "Testing");

To produce:

<Projects>
  <java-xmlbuilder language="Java" scm="SVN">
    <Location type="URL">http://code.google.com/p/java-xmlbuilder/</Location>
  </java-xmlbuilder>
  <JetS3t language="Java" scm="CVS">
    <Location type="URL">http://jets3t.s3.amazonaws.com/index.html</Location>
    <Location2 type="Testing"/>
  </JetS3t>
</Projects>