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CS 483 Enterprise and Web Application Programming

Week 7Web Services

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What are Web Services? W3C (establishes standards for Web

services) defines Web services as: “A Web service is a software system

identified by a URL whose public interfaces and bindings are defined and described using XML. Its definition can be discovered by other software systems. These systems may then interact with the Web service in a manner prescribed by its definition, using XML-based messages conveyed by Internet protocols.”

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What are Web Services? Web services are a result of the natural

evolution of the Web Initially – the Web consisted of sites that

were plain HTML pages Later – Web pages became dynamically

generated Now – Web services provide a

standardized way for applications to expose their functionality over the Web or communicate with other applications over a network – regardless of the app’s implementation, programming language, or computer platform

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Why Implement a Web Service?

Web services can provide a means for an enterprise to: Expand its business offerings Increase the efficiency of it business

processing Improve its customer experience Automate business processing by

streamlining interactions with outside services (e.g., credit card and shipping services)

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Why Implement a Web Service?

Most important reason: Promote interoperability across

different platforms, systems and languages

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Service-Oriented Architecture (SOA)

A Web service enables a service-oriented architecture

SOA is an architectural style that promotes software reusability by creating reusable services

Strategy where applications make use of services available in a network (such as WWW)

SOA addresses complex enterprise environments due to the user of a variety of software and hardware platforms, Internet-based communication, and enterprise application integration (EAI)

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Service-Oriented Architecture (SOA)

Considered the wave of the future. Gartner reports that “By 2008, SOA will be a prevailing

software engineering practice, ending the 40-year domination of monolithic software architecture”

“Through 2008, SOA and Web services will be implemented together in more than 75% of new SOA Web service projects”

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Service A service provides a specific function (usually

business) Service can provide a single discrete function

such as converting one type of currency to another

Service can perform a set of related business functions such as airline reservation system called “course-grained”

SOA is a way of sharing functions in a widespread and flexible way

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Service-Oriented Architecture

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Service-Oriented Architecture

In SOA, you have the following: Service that implements the business logic

and exposes this business logic through well-defined interfaces.

Registry where the service publishes its interfaces to enable clients to discover the service

Clients who discover the service using registries and access the service directly through the exposed interfaces

Loose coupling – means that the client of the service is essentially independent of the service

Client does not have to know much about the service to use it (i.e., implementation language, platform) it just needs to know the interface

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SOA• SOA uses the find-bind-execute paradigm.• In this paradigm, service providers register their service in a public registry. • This registry is used by consumers to find services that match certain criteria. • If the registry has such a service, it provides the consumer with a contract and an endpoint address for that service.

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Benefits of Web Services Interoperability in a heterogeneous

environment Allows distributed services to run on a variety

of software platforms and architectures, and use different languages

Business services through the Web Example – supply chain management

Integration with existing systems Provide developers with standard ways to

access middle-tier and back-end services or legacy systems and integrate them with other applications

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Benefits of Web Services Freedom of choice

Large number of choices for tools, products and technologies to enhance developer productivity

Support multiple clients Java, Microsoft, wireless, etc

Programming productivity Web services create a common

programming environment for faster development

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Web Services Infrastructure and Components

Security

Service descriptions (in WSDL)

Applications

Directory service

Web Services

XML

Choreography

SOAP

URIs (URLs or URNs) HTTP, SMTP or other transport

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Challenges of Web Services Development

Key challenge today is that Web services are still in their infancy Evolving technologies and products

Security More important than ever! Exchange and distribute data requires

top security Key issues:

reliability, availability, and scalability

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Web Services Protocols and Technologies

Web services approach is based on a maturing set of standards that are widely accepted and used

This enables clients and services to communicate and understand each other across a wide variety of platforms and across language boundaries

These are: XML SOAP WSDL Emerging standards

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XML eXtensible Markup Language (XML) has become the

de facto standard for describing data to be exchanged on the Web

An XML tag identifies the information in a document and the structure of a document

For example:<bookshelf> <book> <title>My Life and Times</title> <author>Felix Harrison</author> <price>39.95</price> </book?</bookshelf>

XML document typically associated with a schema that specifies what tags are allowed, their structure, and their meaning

Adopted as the language of Web services

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Simple Object Access Protocol (SOAP)

Though agreeing on the meaning and structure of XML tags makes the use of XML an effective way to exchange data, it's not sufficient for data interchange over the Web. For instance, you still need some agreed-upon

protocol for formatting an XML document so that the receiver understands what the main, "payload," part of the message is, and what part contains additional instructions or supplemental content.

That's where Simple Object Access Protocol (SOAP) comes in.

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Simple Object Access Protocol (SOAP)

SOAP is an XML-based protocol for exchanging information in a distributed environment.

SOAP provides a common message format for exchanging data between clients and services.

The basic item of transmission in SOAP is a SOAP message, which consists of a mandatory SOAP envelope, an optional SOAP header, and a mandatory SOAP body.

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SOAP Message Soap Envelope

specifies XML namespace

names that can be used in message

encoding style – data types recognized

in message Header

usually used to convey security-related information to be processed

Body Main part of message

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SOAP Message Example – Retrieve the Price of a Book

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SOAP Messages A related standard called SOAP

Messages with Attachments (SAAJ) specifies the format of a SOAP message that includes attachments For example – images

SOAP messages are transported using protocols such as HTTP or SMTP

SOAP messages are platform and operating system independent

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Web Service Description Language (WSDL)

WSDL is an XML document that is a description of the Web service’s interface

WSDL defines an XML schema for defining a Web service

Describes the format client uses in making a request for a service

Defines the request itself To uncover the description of a Web service, a

client needs to find the service’s WSDL document

Most common way is for the client to find a pointer to the WSDL document in the Web service’s registration

This is done in an UDDI registry or ebXML registry

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Web Service Description Language (WSDL)

Typical scenario Business registers its service in a UDDI

(Universal Description, Discovery, and Integration) registry or ebXML registry

Registry entry includes a pointer to the WSDL file that contains the WSDL document for the service

Client searches the registry and finds the service

Programmer uses the interface information in the WSDL document to construct the appropriate calls to the service

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UDDI UDDI defines how to publish and discover

information about services in a UDDI-conforming registry Identifies the types of XML data structures

that comprise an entry in the registry for a service

Think of it as a “yellow pages” for Web services

Provides name of service Brief description of what it does Address where it can be accessed Description of the interface for accessing the

service

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UDDI Example - BooksToGo

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Emerging Standards WS-Security

Standard released in March 2004 Describes security-related enhancements to

SOAP messaging that provide for message integrity and confidentiality

Integrity means that the SOAP message is not tampered with as it travels from a client to its final destination

Confidentiality means that a SOAP message is only seen by intended recipients

Quite flexible and can be used with security models and encryption technologies

Public-key infrastructure (PKI) Secure Sockets Layer (SSL)

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Emerging Standards SAML

Security Markup Assertion Language XML-based framework for exchanging

security information Through SAML, multiple services can

exchange security information Can do things like single sign-on for

accessing multiple, related services

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Emerging Standards WS-BPEL

Web Services Business Process Execution Language

XML-based language for coordinating Web services

Example – processing a purchase order – involves multiple steps performed in a specific sequence that need to act like a unit

WS-BPEL uses WSDL to describe Web services that participate in a process and how the services interact

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Realizing SOA with Web Services with Sun

Sun's Java Web Services Developer Pack 1.5 (Java WSDP 1.5) and Java 2 Platform, Enterprise Edition (J2EE) 1.4 can be used to develop state-of-the-art web services to implement SOA.

The J2EE 1.4 platform enables you to build and deploy web services in your IT infrastructure on the application server platform.

It provides the tools you need to quickly build, test, and deploy web services and clients that interoperate with other web services and clients running on Java-based or non-Java-based platforms.

It enables businesses to expose their existing J2EE applications as web services.

Servlets and Enterprise JavaBeans components (EJBs) can be exposed as web services that can be accessed by Java-based or non-Java-based web service clients.

J2EE applications can act as web service clients themselves, and they can communicate with other web services, regardless of how they are implemented.

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Sun Web Service APIs

Java API for XML Processing (JAXP)

This API lets you process XML documents by invoking a SAX or DOM parser in your application. JAXP 1.2 supports W3C XML Schema.

Java API for XML-based RPC (JAX-RPC)

This is an API for building and deploying SOAP+WSDL web services clients and endpoints.

Java APIs for XML Registries (JAXR)

This is a Java API for accessing different kinds of XML registries. It provides you with a single set of APIs to access a variety of XML registries, including UDDI and the ebXML Registry. You don't need to worry about the nitty-gritty details of each registry's information model.

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Sun Web Service APIsSOAP with Attachments API for Java (SAAJ)

This API lets you produce and consume messages conforming to the SOAP 1.1 specification and SOAP with Attachments note.

JSR 109: Web services for J2EE

JSR 109 defines deployment requirements for web services clients and endpoints by leveraging the JAX-RPC programming model. In addition, it defines standard deployment descriptors using the XML Schema, thereby providing a uniform method of deploying web services onto application servers through a wide range of tools.

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Sun Web Service APIs With these APIs, you can focus on high-

level programming tasks, rather than low-level issues of XML and web services.

You can start developing and using Java WSDP 1.5 and J2EE 1.4 web services without knowing much about XML and web services standards.

You only need to deal with Java semantics, such as method invocation and data types.

The dirty work is done behind the scenes, as discussed further in the next section.

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Web Services Publish-Discover-Invoke Model

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Java Client Calling a J2EE Web Service

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J2EE 1.4 Platform Architecture