The transport is the layer that carries SOAP messages. In this section we shall look at HTTP, Message and SMTP transport for carrying SOAP messages.

HTTP is the most common form of binding for SOAP messages. The request message is sent over http from the client to server. The response message from the server also travels over http to the client. For HTTP transport the binding is set to http://schemas.xmlsoap.org/soap/http in the WSDL.

The following shows sample SOAP request and response messages with HTTP headers

<?xml version="1.0" encoding="UTF-8"?>

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<soapenv:Body>

<Test>

<Ones>1</Ones>

<Two>three</Two>

</Test>

</soapenv:Body>

</soapenv:Envelope>

<?xml version="1.0" encoding="UTF-8"?>

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<soapenv:Body>

<Test>

<Ones>1</Ones>

<Two>three</Two>

</Test>

</soapenv:Body>

</soapenv:Envelope>

JMS/MQ provides MOM based channel for carrying messages. MOM products offer asynchronous delivery, guaranteed delivery, once only delivery, persistent messages that can be used for Web Services. The following shows Web Service implementation using JMS server.

In the above framework the Web Service gives the price for the part requested and the SOAP message is transported using a JMS server like Weblogic or SonicMQ.

The SOAP Client constructs the message that contains the part ID for which the price is required. It invokes the AXIS Client that checks the transport. Since the transport is for JMS the JMSSender gets the message and puts it in the request Queue. The JMSListener receives the message and creates an instance of AXIS Server that invokes the corresponding web service. The web service gives the response that is got by the AXIS Server. This is placed in the response Queue and the JMS Sender gets the response that is passed to the SOAP client.

SMTP is very widely used like HTTP and can also be used for carrying SOAP messages. Some of the advantages are its widespread use, asynchronous, store and forward. Hence one way messaging and two way using correlation of the request and response are possible using SMTP for SOAP. For SMTP the binding is set to http://schemas.pocketsoap.com/soap/smtp in the WSDL.

<?xml version=3D"1.0" encoding=3D"UTF-8"?>

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle=3D"http://schemas.xmlsoap.org/soap/encoding/"

xmlns:SOAP-ENC=3D"http://schemas.xmlsoap.org/soap/encoding/"

xmlns:SOAP-ENV=3D"http://schemas.xmlsoap.org/soap/envelope/"

xmlns:xsd=3D"http://www.w3.org/2001/XMLSchema"

xmlns:xsi=3D"http://www.w3.org/2001/XMLSchema-instance">

<SOAP-ENV:Body>

<m:echoString xmlns:m=3D"http://soapinterop.org/">

<inputString>get your SOAP over SMTP here !</inputString>

</m:echoString>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

<?xml version=3D"1.0" encoding=3D"UTF-8"?>

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle=3D"http://schemas.xmlsoap.org/soap/encoding/"

xmlns:SOAP-ENC=3D"http://schemas.xmlsoap.org/soap/encoding/"

xmlns:SOAP-ENV=3D"http://schemas.xmlsoap.org/soap/envelope/"

xmlns:xsd=3D"http://www.w3.org/2001/XMLSchema"

xmlns:xsi=3D"http://www.w3.org/2001/XMLSchema-instance">

<SOAP-ENV:Body>

<m:echoStringResponse xmlns:m=3D"http://soapinterop.org/">

<return>get your SOAP over SMTP here !</return>

</m:echoStringResponse>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

This is similar to JMS Transport except that there is a SMTP Handler for sending mails and a SMTP listener to get the mails at the server end. The following diagram shows framework for using SMTP transport for SOAP messages.

For POP the receiver polls the server to get all the incoming mails and processes the requests by calling the Web Service.

SOAP http://www.w3.org/TR/SOAP/

WSDL http://www.w3.org/TR/wsdl

UDDI http://www.uddi.org/

AXIS http://ws.apache.org/axis/index.html

WS-Conversation http://dev2dev.bea.com/technologies/webservices/SOAPConversation.jsp

SMTP Binding for SOAP http://www.pocketsoap.com/specs/smtpbinding/

SMTP/SOAP http://www7b.boulder.ibm.com/wsdd/library/techarticles/0212_hygh/hygh.html

JMS/SOAP http://www-106.ibm.com/developerworks/webservices/library/ws-jms/index.html?dwzone=webservices

Abbreviations

SOAP Simple Object Access Protocol

UDDI Universal Description Discovery and Integration

WSDL Web Services Description Language

RPC Remote Procedure Call

JMS Java Messaging Service

MQ IBM MQSeries

HTTP Hyper Text Transmission Protocol

SMTP Simple Mail Transfer Protocol

POP Post Office Protocol

Axis Web Services

Axis has four styles of Web Services that can be deployed. These are

• RPC
• Document
• Wrapped
• Message

Document/Wrapped: The Document/Wrapped services are similar and both used XML Schema rather than SOAP encoding for the data. Axis uses Java binding for the XML data.

The following sample contains a SOAP message with a purchase order

<soap:Envelope xmlns="http://xml.apache.org/axis/wsdd/"

xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">

<soap:Body>

<myNS:PurchaseOrder xmlns:myNS="http://commerce.com/PO">

<item>SK001</item>

<quantity>1</quantity>

<description>Sushi Knife</description>

</myNS:PurchaseOrder>

</soap:Body>

</soap:Envelope>

The schema for this purchase order

<schema targetNamespace="http://commerce.com/PO">

<complexType name="POType">

<sequence>

<element name="item" type="xsd:string"/>

<element name="quantity" type="xsd:int"/>

<element name="description" type="xsd:string"/>

</sequence>

</complexType>

<element name="PurchaseOrder" type="POType"/>

</deployment>

For a document style web service the PurchaseOrder is sent as an object from the client.

This would be <method>(PurchaseOrder po).

For a wrapped style service the <PurchaseOrder> Element is just a wrapper for the item,quantity and description. The method would be <method>(String item,int quantity,String description)

Krishnakumar B : Consultant Mindtree Consulting – Bangalore INDIA

Email : b_krishnakumar@mindtree.com

I am a Consultant with Mindtree Consulting based in Bangalore India. I work on Web Services and J2EE related technologies and am currently involved with trying to build applications using Web Services.