Chapter 10. Using XML Documents

Abstract

The pure XML payload format provides an alternative to the SOAP binding by allowing services to exchange data using straight XML documents without the overhead of a SOAP envelope.

XML binding namespace

The extensions used to describe XML format bindings are defined in the namespace http://cxf.apache.org/bindings/xformat. Apache CXF tools use the prefix xformat to represent the XML binding extensions. Add the following line to your contracts:
xmlns:xformat ="http://cxf.apache.org/bindings/xformat"

Hand editing

To map an interface to a pure XML payload format do the following:
  1. Add the namespace declaration to include the extensions defining the XML binding. See the section called “XML binding namespace”.
  2. Add a standard WSDL binding element to your contract to hold the XML binding, give the binding a unique name, and specify the name of the WSDL portType element that represents the interface being bound.
  3. Add an xformat:binding child element to the binding element to identify that the messages are being handled as pure XML documents without SOAP envelopes.
  4. Optionally, set the xformat:binding element's rootNode attribute to a valid QName. For more information on the effect of the rootNode attribute see the section called “XML messages on the wire”.
  5. For each operation defined in the bound interface, add a standard WSDL operation element to hold the binding information for the operation's messages.
  6. For each operation added to the binding, add the input, output, and fault children elements to represent the messages used by the operation.
    These elements correspond to the messages defined in the interface definition of the logical operation.
  7. Optionally add an xformat:body element with a valid rootNode attribute to the added input, output, and fault elements to override the value of rootNode set at the binding level.
Note
If any of your messages have no parts, for example the output message for an operation that returns void, you must set the rootNode attribute for the message to ensure that the message written on the wire is a valid, but empty, XML document.

XML messages on the wire

When you specify that an interface’s messages are to be passed as XML documents, without a SOAP envelope, you must take care to ensure that your messages form valid XML documents when they are written on the wire. You also need to ensure that non-Apache CXF participants that receive the XML documents understand the messages generated by Apache CXF.
A simple way to solve both problems is to use the optional rootNode attribute on either the global xformat:binding element or on the individual message’s xformat:body elements. The rootNode attribute specifies the QName for the element that serves as the root node for the XML document generated by Apache CXF. When the rootNode attribute is not set, Apache CXF uses the root element of the message part as the root element when using doc style messages, or an element using the message part name as the root element when using rpc style messages.
For example, if the rootNode attribute is not set the message defined in Example 10.1, “Valid XML Binding Message” would generate an XML document with the root element lineNumber.

Example 10.1. Valid XML Binding Message

<type ... >
  ...
  <element name="operatorID" type="xsd:int"/>
  ...
</types>
<message name="operator">
  <part name="lineNumber" element="ns1:operatorID"/>
</message>
For messages with one part, Apache CXF will always generate a valid XML document even if the rootNode attribute is not set. However, the message in Example 10.2, “Invalid XML Binding Message” would generate an invalid XML document.

Example 10.2. Invalid XML Binding Message

<types>
  ...
  <element name="pairName" type="xsd:string"/>
  <element name="entryNum" type="xsd:int"/>
  ...
</types>

<message name="matildas">
  <part name="dancing" element="ns1:pairName"/>
  <part name="number" element="ns1:entryNum"/>
</message>
Without the rootNode attribute specified in the XML binding, Apache CXF will generate an XML document similar to Example 10.3, “Invalid XML Document” for the message defined in Example 10.2, “Invalid XML Binding Message”. The generated XML document is invalid because it has two root elements: pairName and entryNum.

Example 10.3. Invalid XML Document

<pairName>
  Fred&Linda
</pairName>
<entryNum>
  123
</entryNum>
If you set the rootNode attribute, as shown in Example 10.4, “XML Binding with rootNode set” Apache CXF will wrap the elements in the specified root element. In this example, the rootNode attribute is defined for the entire binding and specifies that the root element will be named entrants.

Example 10.4. XML Binding with rootNode set

<portType name="danceParty">
  <operation name="register">
    <input message="tns:matildas" name="contestant"/>
  </operation>
</portType>

<binding name="matildaXMLBinding" type="tns:dancingMatildas">
  <xmlformat:binding rootNode="entrants"/>
  <operation name="register">
    <input name="contestant"/>
    <output name="entered"/>
</binding>
An XML document generated from the input message would be similar to Example 10.5, “XML Document generated using the rootNode attribute”. Notice that the XML document now only has one root element.

Example 10.5. XML Document generated using the rootNode attribute

<entrants>
  <pairName>
    Fred&Linda
  <entryNum>
    123
  </entryNum>
</entrants>

Overriding the binding's rootNode attribute setting

You can also set the rootNode attribute for each individual message, or override the global setting for a particular message, by using the xformat:body element inside of the message binding. For example, if you wanted the output message defined in Example 10.4, “XML Binding with rootNode set” to have a different root element from the input message, you could override the binding's root element as shown in Example 10.6, “Using xformat:body.

Example 10.6. Using xformat:body

<binding name="matildaXMLBinding" type="tns:dancingMatildas">
  <xmlformat:binding rootNode="entrants"/>
  <operation name="register">
    <input name="contestant"/>
    <output name="entered">
      <xformat:body rootNode="entryStatus" />
    </output>
  </operation>
</binding>