2.14. FastInfoset

The Fast Infoset specification (ITU-T Rec. X.891 | ISO/IEC 24824-1) describes an open, standards-based "binary XML" format that is based on the XML Information Set. Metro supports this optimized encoding JAX-WS implementation. For ease of deployment, JAX-WS also support a form of HTTP content negotiation that can be used to turn on Fast Infoset during message exchanges. By default, the Fast Infoset encoding is turned off. For more information on how to use this feature see the following section.

The XML Information Set specifies the result of parsing an XML document, referred to as an XML infoset (or simply an infoset), and a glossary of terms to identify infoset components, referred to as information items and properties. An XML infoset is an abstract model of the information stored in an XML document; it establishes a separation between data and information in a way that suits most common uses of XML. In fact, several of the concrete XML data models are defined by referring to XML infoset items and their properties. For example, SOAP Version 1.2 makes use of this abstraction to define the information in a SOAP message without ever referring to XML 1.X, and the SOAP HTTP binding specifically allows for alternative media types that "provide for at least the transfer of the SOAP XML Infoset".

The Fast Infoset specification is jointly standardized at the ITU-T and ISO. The specification is available to all ITU-T sector members and can also be obtained via the corresponding ISO national body in your location. These specifications recommend the use of the MIME type application/fastinfoset, which has been approved by the Internet Engineering Steering Group (IESG) for documents serialized using this format.

FI is an open-source project initiated by Sun Microsystems to provide access to a fast, fully-featured and robust implementation of the Fast Infoset specification. Metro employs the basic Fast Infoset parsers and serializers available from that project.

2.14.1. Using FastInfoset

Content negotiation is completely driven by the client and uses the standard HTTP headers Accept and Content-Type. The initial request is always encoded in XML, but the client has the option of including the MIME type application/fastinfoset as part of the HTTP Accept header list. If the request is received by a Fast Infoset-enabled service, the reply will be encoded in Fast Infoset. The remainder of the conversation between the client and the service will also be encoded in Fast Infoset as long as the client continues to use the same client object (e.g., the same stub instance) to converse with the server. We call this form of negotiation pessimistic, in contrast to the optimistic case in which a client directly initiates a message exchange using the more efficient encoding.

Content negotiation can be enabled in two different ways: (i) by setting a system property on the VM used to run the client, and (ii) by setting a property on the proxy object. In either case, both the property name and its value are identical. For JAX-WS, the name of the property is com.sun.xml.ws.client.ContentNegotiation. In either case, the accepted property values are none (the default) and pessimistic, optimisitc.

Enabling FastInfoset by configuring proxy

// Enabling FI in pessimistic mode
Map<String, Object> ctxt = ((BindingProvider)proxy).getRequestContext();
ctxt.put(JAXWSProperties.CONTENT_NEGOTIATION_PROPERTY, "pessimistic");

Enabling FastInfoset using system property
  java -Dcom.sun.xml.ws.client.ContentNegotiation=pessimistic ...

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