An Introduction to Web Services - Drexel CCI Introduction to Web Services. 2 © Drexel University Software Engineering Research Group (SERG) Web Services Architecture Web Service

1© Drexel University Software Engineering Research Group (SERG)http://serg.cs.drexel.edu

An Introduction to Web Services


Web Services Architecture

Web ServiceContainer

Protocol-SpecificServer

Client

Web Service


Web Services Architecture

SOAP

ClientProtocol-SpecificServer

Web ServiceContainer

Web Service

SOAP overHTTP/S

Native Call


Web Services Architecture (.Net Scenario)

SOAPWeb ServiceContainer

.Net Framework

ClientWeb Service

orApplication

Client

Protocol-SpecificServer

IISWeb Server

Web Service.asmx

Component

SOAP overHTTP/S

Native Call


Web Services Architecture (Java Scenario)

SOAPWeb ServiceContainer

Apache Axis/SOAP

ClientWeb Service

orApplication

Client

Protocol-SpecificServerApacheTomcat

JSP/ServletContainer Web Service

JavaComponent

SOAP overHTTP/S

Native Call


WSDL – The Contract for Invoking a Service

ClientWeb

ServiceInfrastructure

Web ServiceCall

Web ServiceWSDL

Service Spec.

1. Parse Call2. Validate Call Against WSDL3. Validate Pass?

1. YES: Web Service Implementation2. NO: Generate and Return Fault


WSDL – The Web Service Contract

WSDLMessages

Service InterfaceAbstract Definition

Operations

Interface

BindingService Implementation

Concrete Definition Service

Endpoint


Abstract and Concrete Elements of WSDL

<definitions>

</definitions>

<interface name = “myIFace”>

<message name = “myMsg”>

<types>

</types >. . .

</message >. . .

</interface >. . .

<service><binding name = “Binding1”>

</binding >. . .

</service >

Service Definition WSDL Document

AbstractInterface Definition

ConcreteImplementation

Definition


WSDL Structure

ServiceName = <Service_Name>Ports: Collection of Ports

BindingName = <Binding_Name>Type = <PortType_Interface_Name>Operations: Operation Collection

PortType/InterfaceName = <PortType_Interface_Name>Operations: Operation Collection

MessageName = <Nessage_Name>Parts: Collection of Parts

TypeName = <Message_Type>Simple Built In Type ORComplexType: XSD Definition of Type

1..*

1..*

1..*

1..*

Conc

rete

Ab

stra

ct

MessageType

MessageName

Port/Interface Name

BindingName

PartName = <Part_Name>Type = <Message_Type>

OperationName = <Port_type_op_Namee>Input message= <Message_Name>Output message= <Message_Name>

PortBinding = <Binding_Name>Address: Physical Endpoint

Operation Name

OperationName = <Port_type_op_Name>Input name=Logical_In_Op_NameOutput name=Logical_Out_Op_Name


What is WSDL?Web Service Description LanguageSpecifies

Types: types defined for usage in the messagesMessages: the messages being exchanged between a client and a servicePort types / Interfaces: An abstract set of operations supported by one or more endpoints (commonly known as an interface); operations are defined by an exchange of messagesBindings: concrete protocol and data formats for a specific port typeService: a collection of bound ports and addresses

WSDL allows for the automatic generation of service proxies

Conc

rete

Ab

stra

ct


WSDL TypesThe web services standards define a collection of common types, user-defined types can be specified using XML schema

Example: Array of Strings (“ArrayOf_xsd_string”)<wsdl:types>

<schema targetNamespace="urn:DirectoryService" xmlns=“…"><import namespace="http://schemas.xmlsoap.org/soap/encoding/"/><complexType name="ArrayOf_xsd_string"><complexContent><restriction base="soapenc:Array"><attribute ref="soapenc:arrayType" wsdl:arrayType="xsd:string[]"/></restriction>

</complexContent></complexType></schema>

</wsdl:types>


WSDL MessageEach message to and from a web service is modeled via a <message> tagA given message may have 1 or more partsEach message part has a name and a type

<wsdl:message name="getFilesInDirRequest"><wsdl:part name="in0" type="xsd:string"/>

</wsdl:message>

<wsdl:message name="getFilesInDirResponse"><wsdl:part name="getFilesInDirReturn" type="impl:ArrayOf_xsd_string"/>

</wsdl:message>


WSDL PortType / InterfacePortType elements have been renamed to Interface elementsThese elements associate messages with the operations that they will be used forDefines input, output and fault operations

<wsdl:portType name="DirList2"><wsdl:operation name="getFilesInDir" parameterOrder="in0">

<wsdl:input message="impl:getFilesInDirRequest" name="getFilesInDirRequest"/>

<wsdl:output message="impl:getFilesInDirResponse" name="getFilesInDirResponse"/>

</wsdl:operation></wsdl:portType>


WSDL BindingsBindings provide the concrete syntax that must be used to access operations for different protocols

<wsdl:binding name="DirectoryServiceSoapBinding" type="impl:DirList2"><wsdlsoap:binding style="rpc“ transport="http://..."/><wsdl:operation name="getFilesInDir">

<wsdlsoap:operation soapAction=""/><wsdl:input name="getFilesInDirRequest">

<wsdlsoap:body encodingStyle="http://.../" namespace="urn:DirectoryService" use="encoded"/>

</wsdl:input><wsdl:output name="getFilesInDirResponse">

<wsdlsoap:body encodingStyle=“http://.../" namespace="urn:DirectoryService" use="encoded"/>

</wsdl:output></wsdl:operation>

</wsdl:binding>


WSDL ServicesService elements encapsulate one or more physical ports defining an endpoint for the service

Port definition includes the binding reference

<wsdl:service name="DirList2Service"><wsdl:port binding="impl:DirectoryServiceSoapBinding"

name="DirectoryService"><wsdlsoap:address location=

"http://localhost:8080/axis/services/DirectoryService"/></wsdl:port>

</wsdl:service>


WSDL defines a service contract

ProxyComponent

Stub

i.e., WSDL2JavaWSDL

i.e., Java2WSDLComponentImplementation WSDL

WSDL can be generated from an implementation or be usedto generate a proxy class


WSDL is your Service Contract

Approaches:Contract-FirstContract-LastMeet-in-the-Middle


Contract First

ComponentStubWSDL

ComponentProxy

Advantages: Optimized Interface, Portable InterfaceDisadvantages: Hard to develop


Contract Last

ComponentImplementation WSDL

ProxyComponent

Stub

Advantages: No need to know WSDL, EasyDisadvantages: Non-optimized stubs, portability problems are possible


Meet-In-The Middle

ComponentInterface WSDL

ComponentStub

ComponentProxy

Hand-OptimizedWSDL

Blends the advantages of the contract-first and contract-last approaches


SOAP

SOAP is the web service standard for encoding requests and responses to and from web services


SOAP Structure

SOAP

HeaderLanguage, Security, Schema,etc.

Envelope BodyInput/Output Message

Fault Information

ExtensionsAttachments not governed by SOAP schema

Extensions


The Body Section…

Document-Centric or RPC-CentricDoc-Centric is the .Net default, the body contains an xml representation of the request/responseRPC-Centric is the Java default, the body contains name/value pairs of the arguments in the request/response


SOAP Request - .Net


SOAP Response - .Net


SOAP Request – Axis/Java (RPC-Centric)


SOAP Response – Axis/Java (RPC-Centric)

Documents

An Introduction to Web Services - Drexel CCI Introduction to Web Services. 2 © Drexel University Software Engineering Research Group (SERG) Web Services Architecture Web Service