Web services

Web ServicesMichael Weiss

Carleton University

Web site for this tutorial:www.scs.carleton.ca/~weiss/talks/mcetech06

Michael Weiss • Montreal Conference on eTechnologies • May 17-19, 2006

About Me

• PhD (1993), U of Mannheim

• Member of Strategic Technology Group, Mitel (1994-1999)

• Assistant Professor, Carleton U (since 2000)

• Areas of work: service-oriented architecture, feature interaction, patterns, business models, open source

2


Topics Covered

• Service-Oriented Architecture

• Core standards (WSDL, SOAP, UDDI)

• Creating, deploying, and invoking web services with Apache Axis

• Data mapping and business objects

• Service composition

• A look at some advanced issues

3


Web Services

• What are web services? In essence, a technology for application integration based on open standards (HTTP, XML)

• In what sense are they related to the Web (capital “W” to refer to the WWW)?

• In fact, deploying web services over the web is more of an artefact than a necessity ...

• What we care about is the web of services (services assembled from other services)

4


Application Integration

5

Bus

Portal

Applications

User


Defining Web Service

• Loosely coupled, document-based

• Application functionality packaged as a single unit and exposed to the network

• Authentication service

• Flight departure monitoring service

• Mobile payment service

• The first generation of web services were “simple”, in the sense of non-composite, and closed (over existing, trusted relationships)

6


Second Generation Services• Complex, and aggregated from web services

provided by third parties (hence, open)

7

Rate Quotes

Transit Times Duty and

Taxation

Print Shipping

Labels

Shipping

<<uses>> Organizational

Boundaries

Service


Web of Services

• In second generation services, applications are assembled from services dynamically

• Roles of service user and provider blend into what others call servents (eg in P2P)

Service userService provider

Composite services

8

Servent


Vision

• Build your applications

• Dynamically discover and orchestrate the execution of services on the network

• Will be able to choose between alternative implementations of the same service

Application

Services

Implementation

Interface

9

Semant

ics

on demand


Service-Oriented Architecture

• Objectives

• Implementation transparency (common structure, neutral service description)

• Location transparency (no hard binding, web-service agnostic interfaces)

• Roles

• Service Provider

• Service User

• Service Registry

10


Service-Oriented Architecture

11

Service User

Service User

ServiceRegistryServiceRegistry

Service ProviderService Provider

Find

Bind + Invoke

Describe + Publish

UDDI

WSDLSOAP


Web Services Layers

12

Application Services(transaction - eg ticket purchase, information - eg tourist guide)

Application ServicesApplication Services((transactiontransaction - - eg eg ticket purchase, ticket purchase, informationinformation - - eg eg tourist guide)tourist guide)

SOAP, WSDL, UDDISOAP, WSDL, UDDISOAP, WSDL, UDDI

XML, HTTPXML, HTTPXML, HTTP

Collaboration Services(orchestration, matchmaking, translation)

Collaboration ServicesCollaboration Services(orchestration, matchmaking, translation)(orchestration, matchmaking, translation)

Utility Services(security, billing, QoS, metering, routing, transactions, messaging)

Utility ServicesUtility Services(security, billing, (security, billing, QoSQoS, metering, routing, transactions, messaging), metering, routing, transactions, messaging)


Topics Covered


• Core standards (SOAP, WSDL, UDDI)





13


SOAP

• Simple Object Access Protocol

• Cross-platform remote calls (de facto, while technically also document exchange)

• Remote calls (typically) using HTTP as the transport and XML as the encoding

• Designed to be as simple as possible, so to make it easily understood and adopted

• But also complete enough to allow complex data structures to be transmitted

14


SOAP Messages

• SOAP messages are XML documents usually sent over HTTP with a certain format

15


SOAP Messages

• Components of a SOAP message

16

Envelope

Header Body

Payload Fault

1+

optional

required (one)

required (one or more)


SOAP Containers

• Container accepts incoming requests and dispatches them to the service

• Translates between SOAP and the native language of the service (Java, C#, ...)

• Clients only need to know the address of the service, and messages it understands, but not what language, platform, or location

17


SOAP Containers

18


Binding to a Service

• Clients get address and messages from a WSDL description of the service

19


Client Proxy

• The binding process (dynamically) returns a proxy to the remote web service

20


WSDL

• Web Service Description Language

• Neutral format for services to advertise themselves on the network

• In future, we can choose between competing providers of same service (price, ...)

• Components of a WSDL description

• Service > Ports > Operations > Messages

• Generating a WSDL description

21


WSDL Decription

• Components of a web service description

22

Description

Type

1+

Message

1+

Port Type

1+

Operation

1+

Binding

Style

1+

Service

Protocol Port

1+

Binding EndpointRequest Response

1+

optional

required (one)

required (one or more)


Interface

• Consider the interface for a Caching service that allows users to cache content

23

public String findInCache(String key); public void cache(String key, String content)

Caching

findInCache

cache


Messages

24

<wsdl:message name="findInCacheRequest"> <wsdl:part name="key" type="soapenc:string"/> </wsdl:message> <wsdl:message name="findInCacheResponse"> <wsdl:part name="result" type="soapenc:string"/> </wsdl:message>

<wsdl:message name="cacheRequest"> <wsdl:part name="key" type="soapenc:string"/> <wsdl:part name="content" type="soapenc:string"/> </wsdl:message> <wsdl:message name="cacheResponse"/>


Port Type

• Port Type

25

<wsdl:portType name="Caching"> <wsdl:operation name="cache" parameterOrder="key content"> <wsdl:input name="cacheRequest" message="impl:cacheRequest"/> <wsdl:output name="cacheResponse" message="impl:cacheResponse"/> </wsdl:operation>

<wsdl:operation name="findInCache" parameterOrder="key"> <wsdl:input name="findInCacheRequest" message="impl:findInCacheRequest"/> <wsdl:output name="findInCacheResponse" message="impl:findInCacheResponse"/> </wsdl:operation></wsdl:portType>


Service Binding

• Port Type

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<wsdl:binding name="CachingSoapBinding" type="impl:Caching"> <wsdlsoap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/> <wsdl:operation name="cache"> <wsdlsoap:operation soapAction=""/> <wsdl:input name="cacheRequest"> <wsdlsoap:body use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:Cache"/> </wsdl:input> <wsdl:output name="cacheResponse"> <wsdlsoap:body use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:Cache"/> </wsdl:output> </wsdl:operation>

</wsdl:binding>


Service

• Service ties it all together: it defines one or more ports, with binding and endpoint

27

<wsdl:service name="CachingService"> <wsdl:port name="Caching" binding="impl:CachingSoapBinding"> <wsdlsoap:address location= "http://localhost:9090/axis/services/Caching"/> </wsdl:port></wsdl:service>


UDDI

• Universal Discovery and Directory Interface

• Service discovery protocol

• Kind of yellow pages which allows applications to obtain information about businesses and their web services

• Helps potential business partners to find each others’ business services

• A system will have some kind of directory, but not always need all UDDI features

28


Service Directory

• A service directory allows publishers to publish information about their services, and users to locate them (and receive updates)

29

User

Provider

Directory

publish

delete

update

locate: ServiceInformation

subscribe

Service

Information

Service

Implementation


UDDI Structure

• UDDI stores service information in the form of business entities, business services, binding templates and technical models

30

Business

Entity0,,*

Business

Service

Binding

Template

0,,*

0,,*

Technical

Model

0,,*0,,*


Topics Covered







31


Apache Axis

• Open source web service framework

• Client programming model of Axis provides components for client to invoke a service endpoint and receive the response message

• Server programming model based on a listener for each transport protocol, a set of message handlers, and service handlers

• A detailed discussion of its architecture can be found at http://ws.apache.org/axis

32


Apache Axis Architecture

33

Tomcat Servlet Container

Apache

Axis

Servlet

Web

Service 1

Web

Service 2

Web

Service 3

Client


Architecture Adapter

• Frameworks such as Apache Axis allow you to be fully web service-agnostic: to access web services from Java use method calls via architecture adapters (eg Java2WS)

34

Java B

eg .Net


Step by Step Guide to Axis

1. Provide a Java interface or class that describes the service interface

2. Create WSDL using Java2WSDL tool3. Create bindings through WSDL2Java tool4. Implement the service interface5. Deploy the service6. Implement clients using generated stubs

35


Axis Artefacts and Flow

36

Service

Interface

WSDL

Java2WSDL

Service

Interface

Service

Locator

Service

Stub

WSDL2Java

Client-side files Server-side files

WSDD

Deploy

Service

Binding

Service

SkeletonService

WSDD

Undeploy

WSDL2Java

(optional)

Generated User-

defined


Provide a Java Interface

• Define the functionality you want to expose as a web service using an interfacepackage cache;

public interface Caching { public String findInCache(String key); public void cache(String key, String content)}

37

Caching

findInCache

cache

1


Interface Segregation

• Achieve greater coherence by limiting your interfaces to related methods

• Implement multiple ports in one service

38

ContentProviderRetrieval

Billing

Billing

processBilling

Retrieval

retrieveArticle


Create WSDL from Java

• Create the WSDL (Caching.wsdl) from the Java interface defined earlier• -o name of output file

• -l location of web service

• -n target namespace of the WSDL document

• -p mapping of namespace to packages

java org.apache.axis.wsdl.Java2WSDL -o "cache/Caching.wsdl" -l "http://localhost:8080/axis/services/Caching" -n "urn:Cache" -p"cache" "urn:Cache" cache.Caching

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2

step2.sh


Create WSDL from Java

• Conversion to WSDL will also generate XML types (using XML Schema) for all non-primitive types references in the interface

• Supports bean classes, enumeration classes, arrays, and holder classes (inout)

• No types in this simple example, but a more complex one will be presented later

40


Create Bindings from WSDL

• While we can create our SOAP messages to invoke a service at runtime (more later), ...

• ... it is generally better to use WSDL2Java to convert a WSDL file into Java stubs

41

3


Create Bindings from WSDL

• Create a (static) client-side architecture adapter using the WSDL2Java tool• -o name of output file

• -N mapping of namespace to target package

• Adapter classes created• public interface CachingService

• public class CachingServiceLocator

java org.apache.axis.wsdl.WSDL2Java -o . \ -Nurn:Cache cache.stubs cache/Caching.wsdl

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step3.sh


Implement Service Interface

• Implement the service by implementing the Caching interface

43

4

public class Cache implements Caching { protected LinkedHashMap cache = LinkedHashMap(100); public String findInCache(String key) { return (String) cache.get(key); }

public void cache(String key, String content) { cache.put(key, content); }}


• Separating interface from implementation is a core element of loose coupling

Cache

findInCache

cache

Caching

findInCache

cache

Client

Interface-Implementation Separation

44

Dependency InversionPrinciple


Deploy the Service

• In a Web Service Deployment Descriptor (WSDD) tell Axis how to route requests to the correct target (service) class

45

5

<deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:java="http://xml.apache.org/axis/wsdd/providers/java"> <service name="Caching" provider="java:RPC"> <parameter name="className" value="cache.Cache"/> <parameter name="scope" value="Application"/> <parameter name="allowedMethods" value="findInCache cache"/> </service> </deployment>


Start the Axis Server

• If the Axis engine is not running start it:

• as a servlet from within a servlet engine (eg Tomcat): code in webapps/axis

• or as a standalone server (here ... and for testing and simple applications)

• Invoking the standalone SimpleAxisServer

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java org.apache.axis.transport.http.SimpleAxisServer \ -p 9090 axis.sh


AdminClient

• Make the service available to clients by deploying it using the AdminClient

• If deploying to the standalone Axis server, also supply the port number

• Now we are ready to invoke the service

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> java org.apache.axis.client.AdminClient \ -p 9090 deploy.wsddProcessing file cache/deploy.wsdd<Admin>Done processing</Admin>

admin.sh


Create the Client

• There are two ways to invoke a service

• Dynamic client: create a Call object for each method at runtime

• Static client: generate a static proxy from the WSDL description

48

5


Dynamic Client

49

public class DirectCachingClient { public static void main(String[] args) { try { String endpoint = "http://localhost:9090/axis/services/Caching"; Service service = new Service(); Call call = (Call) service.createCall(); call.setTargetEndpointAddress(new java.net.URL(endpoint)); call.setOperation("findCache"); call.setReturnType(XMLType.XSD_STRING); String ret = (String) call.invoke( new String[] {"theAnswer"}); System.out.println("Received: " + ret); } catch (Exception e) { System.err.println("Exception: " + e); } }}


Static Client

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public class CachingClient { public static void main(String[] args) { try { CachingService service = new CachingServiceLocator(); Caching port = service.getCaching(); // to access the service at a different endpoint: // Caching port = service.getCaching(url); String answer = port.findInCache("theAnswer"); if (answer == null) { port.cache("theAnswer", "42"); } answer = port.findInCache("theAnswer"); System.out.println(answer); } catch (Exception e) { System.err.println("Exception: " + e); } }}


Setting up Axis

• Download Apache Axis from website

• http://ws.apache.org/axis

• Latest stable release is axis-bin-1_4.zip

• Install in a directory and put the .jar files in the axis/lib directory into your class path

• In my Unix shell, I would say

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set AXIS_HOME="$home/axis"set CLASSPATH="${CLASSPATH}:$AXIS_HOME/lib/axis-ant.jar"set CLASSPATH="${CLASSPATH}:$AXIS_HOME/lib/axis.jar"...


Axis User Guide

http://ws.apache.org/axis/java/user-guide.html

52

for more information


Case Study: Bookstore

• As a larger example, consider an application for ordering books from multiple stores

• This application needs to provide a portal through which users can place orders

• It invokes the (different?) order processing services provided by the bookstores

• First, the big picture ...

53


WSDL Repository/

UDDI Registry

Bookstore

1

Bookstore

2

Bookstore

3

Axis Engine

OrderProcessing

Stub 1OrderProcessing

Stub 1WSDL

Client

StubsPortal

OrderProcessing

Stub(s)

Deploy

Invoke

Actual

calls

1

1

2

3

4

5

Actors and Interactions

54


Interface

• The bookstore exposes an OrderProcessing interface through which to place orders

• Orders can also be canceled given their OID

55

public interface OrderProcessing { public String processOrder(String customer, String[] isbns, int[] quantities); public void cancel(String oid);}

Bookstore

processOrder

cancel

OrderProcessing


WSDL and Stubs

• Generate the WSDL from the interface

• Generate client stubs from the WSDL

56

step2.sh bookstore_v1 OrderProcessing Bookstore \ bookstore_v1

OrderProcessing.wsdl

step3.sh bookstore_v1 OrderProcessing Bookstore \ bookstore_v1.stubs

OrderProcessingServiceLocatorOrderProcessingServiceOrderProcessingOrderProcessingStub


Service (1)

• Much of the following code is stubbed out, as it is not related to web services

57

public class Bookstore implements OrderProcessing { // ... public String processOrder(String customer, String[] isbns, int quantities[]) { String oid = generateOid(); Order order = new Order(customer, isbns, quantities); orders.put(oid, order); // do whatever else to initiate payment processing // and shipping (not shown ...) return oid; }


Service (2)

• And to finish off ...

58

// ...

public void cancel(String oid) { Order o = (Order) orders.get(oid); if (o != null) { orders.remove(oid); // do whatever is needed to cancel the order } } private String generateOid() { return "o" + nextOid++; }}


Deploy the Service

• Deployment descriptor for the bookstore is similar to that for the Caching service

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<deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:java="http://xml.apache.org/axis/wsdd/providers/java"> <service name="OrderProcessing" provider="java:RPC"> <parameter name="className" value="bookstore_v1.Bookstore"/> <parameter name="scope" value="Application"/> <parameter name="allowedMethods" value="processOrder cancel"/> </service> </deployment>


Client

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public class BookstoreClient { public static void main(String[] args) { try { OrderProcessingService service = new OrderProcessingServiceLocator(); OrderProcessing port = service.getOrderProcessing(); String oid = port.processOrder("[email protected]", new String[] {"123456", "732541"}, new int[] {2, 1}); System.out.println("order " + oid + " placed"); port.cancel(oid); System.out.println("order " + oid + " canceled"); } catch (Exception e) { System.err.println("Exception: " + e); } }}


Topics Covered







61


Business Objects

• Represent highly cohesive business concepts such as order, line item, or address

• Also known as data objects or beans, ie they only contain data access operations

• Business objects often collected in groups

• But rich object structures are in conflict with the flat nature of web services

• Focus of web services on loose coupling, so unlike CORBA or RMI no OO focus

62


Taking Orders now!

• Business objects can contain primitive and complex data as in the Order example

63

Order

customer: String

lineItems: LineItem[]

setCustomer

getCustomer: String

setLineItems

getLineItems: LineItem[]

LineItem

isbn: String

quantity: int

setIsbn

getIsbn: String

setQuantity

getQuantity: int

*


Data Mapping to XML

• Basic mapping defined by JAX-RPC spec

• Mapping of primitive types

• Complex types that follow the JavaBeans convention (BeanSerializer)

• Arrays and some Collection types

• Exceptions

• Key consideration is the interoperability between SOAP implementations !

64


Mapping of Primitive Types

• Primitive typesdefined instandard SOAPencoding

65


Complex Types

• Axis can serialize and deserialize any classes that follow the JavaBeans convention ...

• ... without requiring you to write any code !

• Simple properties• setAddress and getAddress

• Indexed properties (arrays of values)• Customer[]• setCustomers and getCustomers

66


Bean Mapping

• Need to define a bean mapping in WSDD by adding a <beanMapping> tag

• Maps a Java bean to an XML qualified name (qname) associated with a namespace

<beanMapping qname="ns:Order" xmlns:ns="urn:Bookstore" languageSpecificType="java:bookstore_v2.Order"/>

67


Orders in XML

• XML schema for the Order type

68

<complexType name="Order"> <sequence> <element name="customer" type="soapenc:string" .../> <element name="lineItems" type="impl:ArrayOfLineItem" .../> </sequence></complexType>

<complexType name="LineItem"> <sequence> <element name="isbn" type="soapenc:string" .../> <element name="quantity" type="xsd:int" .../> </sequence></complexType>


Order (simple)

• The Java Beans convention distinguishes simple and indexed properties

public class Order { protected String customer; public String getCustomer() { return customer; }

public void setCustomer(String customer) { this.customer = customer; } // ...

69


Order (indexed)

• In the Order class, line items are indexed

// ...

private LineItem[] lineItems; public LineItem[] getLineItems() { return lineItems; } public void setLineItems(LineItem[] lineItems) { this.lineItems = lineItems; }}

70


Arrays and Collections

• Some Java collections (Vector, Hashtable, ...) have serializers, but interoperability between SOAP implementations in not guaranteed

• Most reliable way, thus, is to use arrays

<complexType name="ArrayOfLineItem"> <complexContent> <restriction base="soapenc:Array"> <attribute ref="soapenc:arrayType" wsdl:arrayType="impl:LineItem[]"/> </restriction> </complexContent></complexType>

71


Bookstore

• New interface to our bookstore that uses business objects (ie Order)

72

public class Bookstore implements OrderProcessing { // ...

public String processOrder(Order order) { String oid = generateOid(); orders.put(oid, order); // do whatever else to initiate payment processing // and shipping (not shown ...) return oid; }

// ...}


Bookstore Clientpublic class BookstoreClient { public static void main(String[] args) { try { OrderProcessingService service = new OrderProcessingServiceLocator(); OrderProcessing port = service.getOrderProcessing(); Order order = new Order("[email protected]", new LineItem[] { new LineItem("123456", 2), new LineItem("732541", 1) }); String oid = port.processOrder(order); System.out.println("order " + oid + " placed"); port.cancel(oid); System.out.println("order " + oid + " canceled"); } catch (Exception e) { System.err.println("Exception: " + e); } }}

73


WSDD for Bookstore

• Define complex types on which the service implementation relies in the WSDD

• namespace (urn:Bookstore)

• serializers (beanMapping to ns:Order)<deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:java="http://xml.apache.org/axis/wsdd/providers/java"> <service name="OrderProcessing" provider="java:RPC"> <parameter name="className" value="bookstore_v2.Bookstore"/> <parameter name="allowedMethods" value="processOrder cancel"/> <beanMapping qname="ns:Order" xmlns:ns="urn:Bookstore" languageSpecificType="java:bookstore_v2.Order"/> <beanMapping qname="ns:LineItem" xmlns:ns="urn:Bookstore" languageSpecificType="java:bookstore_v2.LineItem"/> </service></deployment>

74


Topics Covered







75


Business Processes

• Means by which one or more activities are accomplished in an operating business

• Business process models include

• Roles of users

• Definition of activities

• Can be represented diagrammatically as as activity diagrams, use case maps, ...

• Concerned with structure and interfaces

76


Business Process Components

• Business processes model business operation, vs business objects which model (data) entities within a business

• Purely look at a business from the aspect of the activities the business conducts

• Activities can be composed into larger business processes, and may be business processes themselves, or web services

• We are concerned with composition

77


Ordering Process

78

Select Products

to Order

Enter Customer

Information

Submit Product

OrderCreate Order

Remove from

Warehouse

Ship ProductsReceive

Products

Customer Store


Business Processes in Practice

• Business process concepts overlap with existing architectures and styles

• The tended to be part of the custom logic outside the business object model

• Business process implementations differ largely between organizations

• Large business processes often span multiple companies (need to integrate processes)

• Motivates need to support fluidity

79


Business Process Modeling

• Several standards for modeling and representing business processes

• Business Process Execution Language (BPEL)

• IBM, Microsoft, BEA

• Business Process Modeling Language (BPML)

• XML-based explicit representation of business process flow model

80


Marginalized Objects

• We have discussed this before ...

• Applied to business processes this means that business processes require a flat component model with interface definition and implementation

• Each interface is implemented as the composition of web services

• Also applied to flow logic by moving it out from the programming language (BPEL !)

81


Process Logic in BPEL

Client Web Service

businessProcess()

BPEL Container

invoke()

receive()

reply()

wait()

terminate()

sequence()

pick()

flow()

BPEL Flows

82


Business Process Pattern

<<interface>>BusinessActivity

run()

BusinessActivityImpl

run()

<<interface>>BusinessProcess

run()

ActivitySequence

next()

get()

Data

get()

set()

BusinessProcessImpl

run()

83


Participants

• BusinessProcess

• Interface to the business process

• BusinessProcessImpl

• Logic of the business process, which can be a simple ActivitySequence

• ActivitySequence

• Sequence of business activities that must occur before process is complete

84


More Participants

• Data

• Captures side effects of business activities (in this pattern: a shared data pool)

• BusinessActivity

• Unit of work in the business process, which may itself be a process, a service, or just a single method on an object

85


Ordering Process

• Customer submits an order

• Business process puts order into data pool

• ... determines if products exist (success) in warehouse, and reserves them

• ... checks state of data pool and launches create order business activity

• ... notifies warehouse staff to ship

• ... returns an order identifier to the user

86


Product Order Process<<interface>>

BusinessActivity

setData()

run()

isComplete()

getReturnValue()

isSuccessful()

CreateOrder

run()RemoveProduct

Quantity

run()

ActivitySequence

next()

get()

ProductOrderImpl

createProductOrder()

run()

ShipProducts

run()

BusinessProcess

run()

ProductOrderWebService

createProductOrder()

Hashtable

87


Topics Covered







88


Advanced Issues

89

Workflows

Mobile Services

QoS/Policy

Security

Coordination

Semantics

WebServices


Client-Server

Desktops

N-Tier

Spaces

Embedded Networks

Agents

Web services

Grids

P2P

Distributed Objects

}

Social Computing

Utility

Semantic Web

Coordination Media

} Semantic Grid

} MirrorWorld

1990's

2000's

20??'sUbiquitous Computing

Convergence

90


Summary• Concepts

• Service-oriented architecture, core standards, data mapping, and business processes

• Principles

• Interface/implementation separation, top-down/bottom-up design, interface segregation, ...

• Patterns

• SOA, Architecture Adapter, Service Directory, Business Object, Service Composition

• Tools

• Apache Axis

91


Further Reading

• Taylor, From P2P to Web Services and Grids: Peers in a Client/Server World, Springer

• Monday, Web Service Patterns, APress

• Pashtan, Mobile Web Services, Cambridge

• Sotomayor, Globus Toolkit 4: Programming Java Services, Morgan Kaufmann

• Papazoglou, Web Services and Cross Enterprise Computing, Addison-Wesley

92