Web Services

Web Services Web Technology - 2ID60 26 November 2013

Katrien Verbert Natasha Stash George Fletcher

Plan for today

•  Recap: Web fundamentals •  APIs, Web Services •  Restful services •  SOAP-based services •  Comparison •  Tutorial

•  JAX-WS: Building SOAP-based services in Java •  JAX-RS: Building RESTful services in Java

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Recap: Web Fundamentals

Key Architectural Components •  Identification: URI •  Interaction: HTTP •  Standardized Document Formats: HTML, XML, JSON, etc.

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URIs / resources

•  URIs identify interesting things •  documents on the Web •  relevant aspects of a data set

•  HTTP URIs name and address resources in Web based systems •  a URI names and identifies one resource •  a resource can have more than one name −  http://foo.com/software/latest −  http://foo.com/software/v1.4

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Resource representation

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Plan for today

•  Recap: Web fundamentals •  APIs, Web Services •  RESTful services •  SOAP-based services •  Comparison •  Tutorial

•  JAX-WS: Building SOAP-based services in Java •  JAX-RS: Building RESTful services in Java

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APIs

What is an API?

and

Why do we need APIs?

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(Web) APIs

•  Application Programming Interface

•  Specifies how software components communicate with each other •  e.g., Java API, 3rd party library APIs •  usually come with documentation

•  Web API: specify how applications communicate with other over the Web (HTTP, URI, XML, etc.)

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Web Services, Web Applications and APIs (Application Programming Interface)

•  Web Applications == Web Services == Web APIs ?

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Web Services, Web Applications and APIs (Application Programming Interface)

•  Web Applications are designed to be accessed by end users through Web client software

•  Web Services are intended to be used by other software applications

•  Web APIs ≈ Web Services

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Web Services

•  “Web Services” � “Web APIs” •  Build on the design principles and architectural

components of the Web •  Provide certain operations

•  Exchange structured data in standard formats (JSON, XML, etc.)

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Web Services

Example operations:

•  Publish image on Flickr •  Order a book at Amazon •  Post a message on your friend’s Facebook wall

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What Are Web Services?

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Example client application

http://ariadne.cs.kuleuven.be/alocom/alocom_plugin/alocom_plugin.swf

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Disaggregation service

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What Are Web Services?

•  W3C definition: •  �A software system designed to support

interoperable machine-to-machine interaction over a network...�

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Web Services Use

•  Connect existing software •  Reusable application components

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Major classes of Web Services

•  Big Web Services (L. Richardson and S. Ruby) •  RESTful (REST-compliant) Web Services

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Overview

•  Introduction •  RESTful services •  SOAP-based services •  Comparison •  Tutorial

•  JAX-WS: Building SOAP-based services in Java •  JAX-RS: Building RESTful services in Java

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A RESTful Web service...

•  ... exposes its data and functionality through interlinked Web resources identified by URI.

•  ... is more data-centric, and less functionality-centric (as opposed to SOAP services).

•  ... embeds functionality of the service in the uniform HTTP interfaces for interaction: GET, PUT, DELETE, POST.

•  ... uses HTTP as the application protocol instead of SOAP

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Four basic design principles

•  Use HTTP methods explicitly. •  Be stateless. •  Expose directory structure-like URIs. •  Transfer XML, JavaScript Object Notation (JSON), or

both.

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Use HTTP methods explicitly

•  One-to-one mapping between •  create, read, update, and delete (CRUD) operations •  and HTTP methods.

•  According to this mapping: •  To create a resource on the server, use POST. •  To retrieve a resource, use GET. •  To change the state of a resource or to update it, use PUT. •  To remove or delete a resource, use DELETE.

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Example: HTTP GET request

GET /users/Robert HTTP/1.1 Host: myserver Accept: application/xml

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Example: HTTP PUT request

PUT /users/Robert HTTP/1.1 Host: myserver Content-Type: application/xml <?xml version="1.0"?>

<user> <name>Bob</name>

</user>

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Be stateless

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Stateful design

Stateless design

Expose directory structure-like URIs

http://www.myservice.org/discussion/topics/{topic} http://www.myservice.org/discussion/{year}/{day}/{month}/{topic} http://www.myservice.org/discussion/2008/12/10/{topic}

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Transfer XML, JSON, or both

<?xml version="1.0"?> <discussion date="{date}" topic="{topic}"> <comment>{comment}</comment> <replies>

<reply from="joe@mail.com" href="/discussion/topics/{topic}/joe"/> <reply from="bob@mail.com" href="/discussion/topics/{topic}/bob"/>

</replies> </discussion>

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Tools and frameworks

•  Ruby on Rails -- a framework for building RESTful Web applications – http://www.rubyonrails.org/

•  Restlet -- framework for mapping REST concepts to Java classes http://www.restlet.org

•  Django - framework for building RESTful Web applications in Python

•  JAX-RC specification (http://jsr311.java.net/) -provides a Java API for RESTful Web Services over the HTTP

•  RESTEasy (http://www.jboss.org/resteasy/) - Jboss project that provides various frameworks for building RESTful Web Services and RESTful Java applications.

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Overview

•  Introduction •  Restful services •  Big web services •  Comparison •  Tutorial

•  JAX-WS: Building SOAP-based services in Java •  JAX-RS: Building RESTful services in Java

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Big web services

•  SOAP (Simple Object Access Protocol) •  WSDL (Web Services Description Language) •  UDDI (Universal Description, Discovery, and

Integration)

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Roadmap

Service Requester

Service Broker (UDDI)

Service Provider

Find (SOAP)

Publish (WSDL)

Bind (SOAP)

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What is SOAP

•  SOAP used to stand for Simple Object Access Protocol •  SOAP is a communication protocol •  SOAP is designed to communicate via Internet •  SOAP is based on XML •  SOAP is simple and extensible •  SOAP is platform and language independent •  SOAP is a W3C standard

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SOAP Message Structure

SOAP Envelope

SOAP Header

SOAP Body

header block

<?xml version='1.0' ?><env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> <env:Header> ... </env:Header> <env:Body> ... <env:Fault> ... </env:Fault> </env:Body> </env:Envelope>

body block

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SOAP Example: RPC-Style Request Message <?xml version='1.0' ?> <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> <env:Body> <ts:getPrice xmlns:ts="http://travelagency.example.org/wsdl/trips" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding"> <ts:departing>Amsterdam (Schiphol)</ts:departing> <ts:arriving>Saint-Petersburg (Pulkovo)</ts:arriving> <ts:departureDate>01-05-2010</ts:departureDate> <ts:/getPrice> </env:Body> </env:Envelope>

Request

<?xml version='1.0' ?><env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope">

<env:Body> <ts:getPriceResponse xmlns:ts="http://travelagency.example.org/wsdl/trips" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding" > <ts:price>180.00</ts:price> </ts:getPriceResponse> </env:Body> </env:Envelope>

Response

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SOAP HTTP Binding: SOAP HTTP Post Usage

POST /pricesService/getPrice HTTP/1.1 Host: http://travelagency.example.org Content-Type: application/soap+xml; charset=utf-8 Content-Length: nnn <?xml version='1.0' ?> <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> <env:Body> <ts:getPrice xmlns:ts="http://travelagency.example.org/wsdl/trips"> <ts:departing>Amsterdam (Schiphol)</ts:departing> <ts:arriving>Saint-Petersburg (Pulkovo)</ts:arriving> <ts:departureDate>21-04-2010</ts:departureDate> <ts:/getPrice> </env:Body> </env:Envelope>

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SOAP HTTP Binding: SOAP Response

HTTP/1.1 200 OK Content-Type: application/soap+xml; charset=utf-8 Content-Length: nnn <?xml version='1.0' ?> <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> <env:Body> <ts:getPriceResponse xmlns:ts="http://travelagency.example.org/wsdl/trips"> <ts:price>180.00</ts:price> </ts:getPriceResponse> </env:Body> </env:Envelope>

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Roadmap

Service Requester

Service Broker (UDDI)

Service Provider

Find (SOAP)

Publish (WSDL)

Bind (SOAP)

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What is WSDL

•  WSDL stands for Web Services Description Language •  WSDL is used to describe and locate Web Services •  WSDL is based on XML •  WSDL is a W3C standard

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WSDL

•  Describes three fundamental properties •  What a service does

•  Operations (methods) provided by the service •  How a service is accessed

•  Data format and protocol details •  Where a service is located

•  Address (URL) details

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WSDL Document Structure

Main structure of WSDL document <definitions targerNamespace=�...�> <types>definition of types...</types> <message>definition of a message...</message> <portType>definition of a port</portType> <binding>definition of a binding...</binding> <service> <port>...</port> </service> </definitions>

WSDL Specification

abstract part

concrete part

types

messages

operations

port types

bindings

service

port

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WSDL Document Example: Abstract Part

<message name="itineraryMsg"> <part name="departing" type="xs:string"/> <part name="arriving" type="xs:string"/> <part name="departureDate" type="xs:date"/> </message> <message name="itineraryRespMsg"> <part name="price" type="xs:string"/> </message> <portType name="pricesPT"> <operation name="getPrice"> <input message="itineraryMsg"/> <output message="itineraryRespMsg"/> </operation> </portType> PAGE 46

Operation Types

Type Definition

One-way The operation can receive a message but will not return a response

Request-response

The operation can receive a request and will return a response

Solicit-response The operation can send a request and will wait for a response

Notification The operation can send a message but will not wait for a response

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Example: One-Way Operation

<message name="newPrices"> <part name="departing" type="xs:string"/> <part name="arriving" type="xs:string"/> <part name="departureDate" type="xs:date"/> <part name="price" type="xs:string"/> </message> <portType name="pricesPT"> ... <operation name="setPrice"> <input message="newPrices"/> </operation> </portType >

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WSDL Document Example: Concrete Part

<service name="pricesService"> <port name="getPriceRPCPort" binding="ts:b1"> <soap:address location="http://travelagency.example.org/pricesService"> </port> </service>

xmlns:ts='http://travelagency.example.org/wsdl/trips'

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Roadmap

Service Requester

Service Broker (UDDI)

Service Provider

Find (SOAP)

Publish (WSDL)

Bind (SOAP)

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What is UDDI

•  UDDI stands for Universal Description, Discovery and Integration •  UDDI a standard for publishing and discovering Web services •  UDDI is a specification for a distributed registry of Web services •  UDDI is built upon standards such as HTTP, XML, XML Schema,

SOAP, WSDL •  UDDI can communicate via SOAP, CORBA, Java RMI Protocol •  UDDI uses WSDL to describe interfaces to Web Services

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Ways to Use UDDI Registry

•  White pages –  name, address, contact person, Web site •  Yellow pages –  types of business, locations, products, services,

categorizations •  Green pages –  technical information about business services, pointers

to WSDL descriptions of the services

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UDDI Data Model: UDDI Core Data Types

Example: http://www.tutorialspoint.com/uddi/uddi_data_model.htm PAGE 53

UDDI Data Model: tModel example

<?xml version="1.0"?> <tModel tModelKey="”>

<name>http://www.getquote.com/StockQuoteService-interface</name> <description xml:lang="en">…</description> <overviewDoc>

<description xml:lang="en”>WSDL Service Interface Document </description> <overviewURL> http://www.getquote.com/services/SQSinterface.wsdl#SingleSymbolBinding </overviewURL> </overviewDoc> <categoryBag> <keyedReference tModelKey="UUID:C1ACF26D-9672-4404-9D70-39B756E62AB4” keyName="uddi-org:types" keyValue="wsdlSpec"/> <keyedReference tModelKey="UUID:DB77450D-9FA8-45D4-A7BC-04411D14E384” keyName="Stock market trading services” keyValue="84121801"/>

</categoryBag> </tModel>

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UDDI: Programmatic Interfaces

•  UDDI Inquiry Interface: –  find_business, find_service, find_tModel, find_binding,

find_relatedBusiness –  get_businessDetail, get_serviceDetail, get_bindingDetail,

get_tModelDetail •  UDDI Publisher Interface: –  save_business, save_service, save_binding,

save_tModel –  delete_business, delete_service, delete_binding,

delete_tModel –  ...!

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Big Web Services Examples

•  http://www.xmethods.com •  http://www.programmableweb.com/

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Web services enable

1.  data exchange between various applications and different platforms 2.  to resolve interoperability issues 3.  applications to function between two different operating systems server 4.  all of the above

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Which of the following is used to locate and describe web services?

1.  SOAP 2.  Web page 3.  WSDL 4.  UDDI

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Overview

•  Introduction •  Restful services •  SOAP-based services •  Comparison •  Tutorial

•  JAX-WS: Building SOAP-based services in Java •  JAX-RS: Building RESTful services in Java

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Big Web Service Operations vs RESTful Web Service URIs

Big WS operations

RESTful WS URIs

getAllUsers() http://example.com/users/ "

getUserById(String id) http://example.com/users/id/{user-id}

getUserByName(…), addUser(…) removeUser(…), updateUser(…)

http://example.com/users/name/{user-name}

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Big Web Services versus REST

•  A SOAP service has a single endpoint •  that handles all the operations •  therefore it has to have an application-specific

interface.

•  A RESTful service has a number of resources •  so the operations can be distributed onto the resources •  and mapped to a small uniform set of operations.

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Comparison: Big Web Services vs RESTful Web Services

•  Big Web Services pros: –  protocol transparency and independence –  existence of tools to hide the complexity –  security

•  Big Web Services cons: –  rudimentary processing protocol –  complexity –  heavyweight architecture –  do not get the benefits of resource-oriented services –  opaqueness

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Comparison: Big Web Services vs RESTful Web Services

•  RESTful Web Services pros: –  simplicity –  lightweight infrastructure –  addressability –  uniform interface –  scalability of stateless RESTful Web Service –  improved performance using JSON

•  RESTful Web Services cons: –  bound to one protocol: HTTP –  only POST and GET can be used in XHTML form –  dealing with large input data - �malformed� URI –  security issues

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Sources

•  Cesare Pautasso,Olaf Zimmermann,Frank Leymann (2008) RESTful Web Services vs. Big Web Services: Making the Right Architectural Decision. Proc. of the 17th International World Wide Web Conference (WWW2008), Bejing, China, April 2008.

•  Alex Rodriguez. (2008). RESTful Web services: The basics. Available at: http://www.ibm.com/developerworks/webservices/library/ws-restful/

•  Cesare Pautasso and Erik Wilde. Design Principles, Patterns and Emerging Technologies for RESTful Web Services. http://dret.net/netdret/docs/rest-icwe2010/

•  Bernhard Hasl. RESTful web service APIshttp://courses2.cit.cornell.edu/info4302_2012fa/lectures/week7/INFO_CS4302_Lecture12.pdf

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k.verbert@tue.nl n.v.stash@tue.nl g.h.l.fletcher@tue.nl

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