grid computing, b. wilkinson, 20043b.1 web services part ii

Grid Computing, B. Wilkinson, 2004 3b.1

Web ServicesPart II


Web Services

From http://www.globus.org


Address of a Web Service

• URIs

Example (URL)

http://www.cs.wcu.edu/webservices/math1

This does not exist, and if did, would only be meaningful to software.


Client-Service Implementation

• Suppose we have found the service and have its WSDL description, i.e. got past step 4.

• In the implementation, it is convenient to use stubs - java classes suitable for web services defined with WSDL.


Client Stub

• Between the client code and the network is a client stub, sometimes called client proxy.

• The client stub is responsible for taking a request from the client and converting the request into a SOAP request on the network - marshalling.

• Also responsible for receiving SOAP responses

on network and converting to a suitable form for client.


Server Stub

• Between the service and the network is a server stub, sometimes called a skeleton.

• Responsible for receiving a SOAP request from the client stub and converting it into a suitable form for the service -unmarshalling.

• Also converts the response from the service into a SOAP message for the client stub.


Web Service Application


Steps

• Client calls client stub.

• SOAP request sent across network

• Server stub receives request and sends request to service

• Service send result to serve stub

• Server stub sends result across network to client stub.

• Client stub sends result to client.


Web Service Application

Call client stubSOAP

requestRequest service

Result returnedSOAP

responseClient receives result


Web Service Description

• Need a way of formally describing a service, what is does, how it is accessed, etc.

• An Interface Description language (IDL)


Web Service Definition Language (WSDL)

A W3C standard XML document that describes three fundamental properties of a service:

• What it is - operations (methods) it provides.• How it is accessed - data format, protocols.• Where it is located - protocol specific network

address.


Elements of a WSDL document


Parts of a WSDL Document

Parts of an WSDL document::• Root definitions - namespaces

• portType definitions - abstract definition of service

• Message definitions - parameters in method signature

• Type definitions - data types

• Binding definitions - to protocols I.e. SOAP over HTTP

• Service definitions - where service is, ports


portType

Describes “What” - an abstract definition of service operation. Uses the elements:

• message definitions - a set of parameters referred to by method signature, decomposed into parts

• type definitions - defines all data types used


Binding

Describes “how” the elements in abstract interface (portType) are converted in actual data representations and protocols e.g. SOAP over HTTP.


port and service

• Describes “where” service is.

• port - describes how a binding is deployed at the endpoint of a network

• service - a named collection of ports

Root definitions

<?xml version=“1.0”?>

<definitions name=“PriceCheck”

targetNamespace=“http://www.skatestown.com/services/PriceCheck”

xmlns:pc=“http://www.skatestown.com/services/PriceCheck”

xmlns:avail=“http://www.skatestown.com/ns/availability”

xmlns:xsd=“http://www.w3.org/2001/XMLSchema”

xmlns:soap=“http://schemas.xmlsoap.org/wsdl/”>

.



.

</definitions>

portType definitions



<portType name=“PriceCheckPortType”>

<operation name=“checkPrice”>

<input message=“PriceCheckRequest”/>

<output message=“PriceCheckResponse”/>

</operation>

</portType>

Message definitions



<message name=“PriceCheckRequest”>

<part name=“sku” type=“xsd:string”/>

</message>

<message name=“PriceCheckResponse”>

<part name=“result” type=“avail:availabilityType”/>

</message>

Type definitions



<types>

<xsd:schema targetNamespace=“http://www.skatestown.com/ns/availability”

xmlns:xsd=“http://www.w3.org/23001/XMLSchema”>

<xmlns:complexType name=“availabilityType”>

<xsd:sequence>

<xsd:element name=”sku” type=“xsd:string”/>

<xsd:element name=“price” type=“xsd:double”/>

<xsd:element name=“quantityAvailable” type=“xsd:integer”/>

</xsd:sequence>

</xmlns:complexType>

</xsd:schema>

</types>

Binding definitions



<binding name=“PriceCheckSOAPBinding” type=“pc:PriceCheckPortType”>

<soap:binding style=“rpc”

transport=“http://schemas.xmlsoap.org/soap/http”/>

<operation name=“checkPrice”>

<soap:operation soapAction=“”/>

<input>

<soap:body use=“encoded”

namespace=“http://www.skatestown.com/services/PriceCheck”

encodingStype=“http://schemas/xmlas.xmlsoap.org/soap/encoding?”/>

</input>

<output>

<soap:body use=“encoded”

namespace=“http://www.skatestpwn.com/services/PriceCheck”

encodingStype=“http://schemas/xmlas.xmlsoap.org/soap/encoding?”/>

</output>

</operation>

Service definitions



<service name=“PriceCheckService”>

<port name=“PriceCheck” binding=“pc:PriceCheckSOAPBinding”>

<soap:address

location=

“http://localhost:8-8-/axis/services/PriceCheck”/>

</port>

</service>

</definitions>


Building a ServicePreliminary to Assignment 1

To build (deploy) a service one has to create:

• a WSDL document for the service• the client stub• the server stub

and test with a client.


Java Web Service (JWS)(The easy way to deploy a service)

• With JWS facility, service code with jws extension in the Axis-enabled web application is interpreted a web service.

• .jws file automatically compiled if necessary when service called.

• Simple and used in assignment 1 but has limitations.


• Could actually use the web service after deployment with JWS without using a WSDL file nor stubs!

• Just use the service URL which would have a .jws extension - need some code in client and service to make SOAP calls.


WSDL from Code

• One can write the service code (as a class or interface) and then use tools to generate the WSDL document.

– Axis Java2WSDL program generates WSDL file (and its scheme).


WSDL from Running Service

• Another Axis tool can generate the WSDL document.directly from a running deployed service.

• add ?wsdl onto service URL.

• Example of this in assignment 1


Stubs from WSDL

• If we have the WSDL document for the service, can use tools to generate client and server stubs:

– Axis WSDL2Java program generates stubs for use on client and server

– Example of this in assignment 1.

grid computing, b. wilkinson, 20043b.1 web services part ii

Documents

service code

client code

client stubbetween

service unmarshalling

client proxy

soap request

networkserver stub

stubserver stub