Faculty of Information Technology 31284 Web Service Development Week 10 – Web services Intro.

Faculty of Information Technology

31284 Web Service Development

Week 10 – Web services Intro

Web Applications

• Presentation-oriented: – PAGE based– App generates Markup pages (HTML, XHTML etc)– “Human oriented”:

• user interacts with page: Request/Response – B2C & B2C

• Service-oriented: “web services”– Service based– Application provides “Remote Procedure Calls/Remote

Methods” – “Machine oriented”:– Application interacts with Application:

• Request/Response (RPC) • Message oriented

Web Services – problems solved

• Before Web: – Traditional approach:

“Remote Procedure Calls” or “Remote Method Invocation”

– Tied to the underlying architecture– Binary message formats– Compatibility issues– Proprietary technologies and implementations– Expensive, Inflexible, Complex– Not firewall friendly

Web services – problems solved

• After Web:– Different vendors attempted HTTP based solutions– Web based RPC:

• Just send and receive plain text via a URL

– XML based RPC:• Send/receive requests as XML

XML-RPC “standard” (http://en.wikipedia.org/wiki/Xml-

rpc)– Language & technology neutral, but not a

standard Influenced standards formalised as SOAP.

Web services - definition

• “Web services are self-contained, self-describing, modular applications that can be published, located, and invoked across the web.”

• “Web service applications are encapsulated, loosely coupled web ‘components’ that can bind dynamically to each other.”

• Web Services a distributed computing platform

W3C web services standard

W3C standard for web services:

• An application (Consumer) connects to another application (Provider) via SOAP

• The Consumer knows how to connect to the Provider because the interface is described with WSDL.

• The Consumer can find the Provider because the provider’s details are published in a UDDI registry.

• Both communicate using the web protocol, HTTP.

• The data exchange is via XML and XML Schema

Web Services Introduction

• “Simple Object Access Protocol”

• SOAP message contains:– Envelope:

describes the message and how to process it

– Header: contains the features of the SOAP message

– Body: contains the primary information for the message receiver

• SOAP works by transmitting XML between the Consumer and Provider.

• Akin to “Snail Mail” – Envelope is like the mail address, Body is like the content of the letter

SOAP is a XML Message format

Calls and responses are sent as SOAP Envelopes.

The message in a SOAP Envelope has a header (optional) and a body.

The Body is for application level data.Parameters, method calls etc.

The Header is for infrastructure level data.Authentication, coordination etc.Header attributes:

actor (none, next, ultimateReceiver)mustUnderstand (1 or 0)

SOAP Request Example

<?xml version="1.0"?><soap:Envelope

xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Body xmlns:m="http://www.example.org/stock">

<m:GetStockPrice>

<m:StockName>IBM</m:StockName>

</m:GetStockPrice>

</soap:Body>

</soap:Envelope>

getStockPrice(“IBM”)

SOAP Request Example

<?xml version="1.0"?>

<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"><soap:Body xmlns:m="http://www.example.org/stock">

<m:GetStockPriceResponse>

<m:Price>34.5</m:Price>

</m:GetStockPriceResponse>

</soap:Body></soap:Envelope>

getStockPrice(“IBM”) 34.5

SOAP Summary

• SOAP is a simple protocol intended for transferring data from one application to another.

• SOAP provides a mechanism for encapsulating RPC calls into SOAP messages (in envelopes).

• SOAP uses existing, recognised standards to solve problems ofdata representation and transport.

Some SOAP downfalls:• No mechanisms for reliability, transactions, security…

• SOAP is, in itself, not adequate for all needs in industrial applications

• Extra standards to add missing functionality include – WS-reliable messaging,– WS-Security– WS-Coordination, WS-Transactions

• How do you know how to invoke a web service?– SOAP only specifies the format for message exchange, it

doesn’t say what the message itself should contain!

– What is the address of the web service?– What are the required parameters?– What protocols are used?

• Web Services Description Language (WSDL) specifies the answers to these questions

WSDL Structure

Service:– collection of endpoints– endpoint = port + binding

Binding: – maps operations to protocols

(e.g. SOAP via HTTP)

Port type: – a set of operations supported

by endpoints (like a function library)

Operation: – abstract description of an

action supported by a service

Message: – typed definition of data

communication (input and output)

WSDL Elements

• <service>– Groups related ports together– eg. If a portType is bound to two protocols, they

are grouped together

• <port>– Specifies the location of the web service

WSDL Elements

</service>

WSDL Elements

• <binding>– Specifies protocols used to invoke web service

• Eg. Is this a SOAP web service? Over HTTP?

– The abstract interface defined in <portType> can be bound to different messaging and transport protocols

• Eg. SOAP over HTTP, SOAP over SMTP, …

WSDL Elements

<soap:binding transport="http://schemas.xmlsoap.org/soap/http" style="document"/>

<soap:body use="literal"/></input><output>

<soap:body use="literal"/></output>

</operation></binding>

• <portType>– Defines the interface (similar to Java interface

definition)

• <operations>– Defines the actions (similar to Java methods)

</operation></portType>

WSDL Elements

• <message>– Defines a set of parameters– Defined messages are referred to in the

<portType> element

</message><message name="addResponse">

</message>

WSDL Elements

• <types>– Defines the data types used– Referred to by <message> elements – Usually uses XML schema to define types

WSDL Elements

<xs:element name="add" type="tns:add"/><xs:complexType name="add"> <xs:sequence>

<xs:element name="arg0" type="xs:int"/><xs:element name="arg1" type="xs:int"/>

</xs:sequence></xs:complexType><xs:element name="addResponse“

type="tns:addResponse"/>…. & so on….

Agenda

• Introduction to Web Services

• Enabling technologies: SOAP and WSDL, UDDI

• JAX-WS

JAX-RPC

• JAX-RPC was the older standard for interfacing web services with Java

• This had several flaws – not so easy to use, mainly dealt with RPC style transactions, not built into Java

• JAX-RPC 2.0 was a refresh & got renamed to JAX-WS

JAX-WS

• Now built into Java 6

• Concept: you write POJO (Plain Old Java Objects) and annotate your code with @WebService and @WebMethod

• (next slides are from Sun Java user group, tech days 2008 (Carol McDonald))

Developing with JAX-WS

Writing service

JAX-WS mapping

Customising

Client side

Client

• We will develop both a server and client using JAX-WS in the labs

Questions?

Faculty of Information Technology 31284 Web Service Development Week 10 – Web services Intro.

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Transcript of Faculty of Information Technology 31284 Web Service Development Week 10 – Web services Intro.

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