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G52IWS: XML Messaging (briefly)

Chris Greenhalgh2007-11-30

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Contents

• Introduction to message-based communication

• SOAP with Attachment API for Java• Provider-less messaging• Messaging with a JAXM provider

See “Developing Java Web Services”, Chapter 9

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Message-based communication

• Send an XML document, not parameters• No necessary response

– But a later message may be a response :-)

“Developing Java Web Services”, figure 3.4

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SOAP with Attachment API for Java

• Defined by Java Community Process JSR-67• Allows explicit construction and unpacking of

SOAP messages using Java• See example client in src/sample/client/SaajClient.java

• Can be used – to implement SOAP clients and servers directly over

HTTP (as in example)– With JAXM to support indirect and asynchronous

communication (see later)

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Recap: SOAP Message structure

“Developing Java Web Services”, figure 4.1

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SOAP: main classes & interfaces

• javax.xml.soap.SOAPMessageFactory – Source of new SOAPMessages

• javax.xml.soap.SOAPMessage – An entire SOAP message, including attachments (not

XML)• javax.xml.soap.SOAPPart,

javax.xml.soap.AttachmentPart.  – SOAP and Attachment Part(s) of a SOAPMessage– SOAP Part has SOAPEnvelope & MIMEHeaders

• javax.xml.soap.SOAPEnvelope – Contains SOAPHeader &SOAPBody

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• javax.xml.soap.SOAPHeader & javax.xml.soap.SOAPHeaderElement

• javax.xml.soap.SOAPBody & javax.xml.soap.SOAPBodyElement – The body and body elements

• javax.xml.soap.SOAPElement – (Interface) Any SOAP-related XML element in a

SOAP message• javax.xml.soap.Node

– Any XML element in a SOAP message (compare XML Document Object Model)

• javax.xml.soap.SOAPFault – Representation of a SOAP Fault

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Using SAAJ with HTTP: client

• javax.xml.soap.SOAPConnection.    – obtained from SOAPConnectionFactory – Supports request/response over HTTP– E.g. from sample client:SOAPMessage rp = conn.call(msg, urlval);

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Using SAAJ/JAXM with no JAXM Provider: server

• Extend javax.xml.messaging.JAXMServlet and implement javax.xml.messaging.ReqRespListener – E.g.

public class ReqRespServlet extends JAXMServlet implements ReqRespListener { public SOAPMessage onMessage(SOAPMessage msg) { //Implement your business logic here return respMsg; }}

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• Servlet runs in container which handles HTTP

• JAXMServlet handles – converting the POSTed SOAP message

(MIME-encoded) into a javax.xml.soap.SOAPMessage

– calling onMessage()– Converting the returned SOAPMessage into

the HTTP response

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Main JAXM classes & interfaces• javax.xml.messaging.OneWayListener

– Interface for receiving a SOAPMessagepublic void onMessage(SOAPMessage msg);

• javax.xml.messaging.ReqRespListener – Interface for receiving a SOAPMessage and replying

public SOAPMessage onMessage(SOAPMessage msg); • javax.xml.messaging.JAXMServlet

– Utility servlet for doing JAXM HTTP-based message receivers• javax.xml.messaging.ProviderConnection

– Interface for communicating with JAXM “Provider” (see later)• javax.xml.messaging.Endpoint

– Endpoint (client or service) identifier; URI

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Recap: Message-Oriented Middleware (MOM)

Application A

Persistence

Adapter API Application BMOMinfrastructureAdapter API

After “Developing Java Web Services” figure 1.6

Messages sent & received

(& transactions contexts)

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JAXM-based application architecture

“Developing Java Web Services”, figure 9.1

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JAXM-based application architecture details

ProviderConntection: allows message sendingand registering of receivers

Logical distributedJAXM provider

OneWayListener orReqRespListener interfaceto receive message(s).Identified by an Endpoint (URI)

Message bean orJAXMServlet

Local API/client

for provider

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Simple JAXM provider realisation

Local API/client

for provider

ProviderInfrastructure

Including persistence

ProviderConnectionw. Endpoint

Messagesbetweenclient andprovider

Messagesto/from

external services

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JAXM Provider• C.f. MOM infrastructure• Handles message transmission and routing

– Including message reliability (through retransmission)• Uses “Profiles” to specify the underlying

messaging protocol– E.g. SOAP-RP (SOAP Routing Protocol) or ebXML

• Handles synchronous vs asynchronous interactions– E.g. mapping asynchronous client request to

synchronous server handling

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Conclusion

• SAAJ allows direct construction/consumption of SOAP messages– No mapping to programming language types

or paradigms (such as RPC)• JAXM supports messaging-style use of

SOAP, in particular asynchronous interactions– E.g. extended business processes