Introduction to Web Services Bina Ramamurthy This work is partially supported by
Introduction to Web Services
Bina Ramamurthy bina@cse.buffalo.edu
This work is partially supported by
NSF-DUE-CCLI-A&I Grant 0311473
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Topics for Discussion
Webservices and Service Oriented
Architectures (SOA)
XML (eXtensible Markup Language)
SOAP (Simple Object Access Protocol)
WS (Web Services)
Summary
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Web Services and SOA
Web Services is a technology that allows for applications to communicate with each other in a standard format.
A Web Service exposes an interface that can be accessed through XML messaging.
A Web service uses XML based protocol to describe an operation or the data exchange with another web service. Ex: SOAP
A group of web services collaborating accomplish the tasks of an application. The architecture of such an application is called Service-Oriented Architecture
(SOA).
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SOA in Real World: Report in
InfoWorld, May 2, 2005 Issue 18
http://www.infoworld.com/article/05/05/02/18FEsoabt_1.html?WEB%20SERVICES
State of Massachusetts uses SOA to deliver healthcare services. With
HTML web application it had no control of look and feel and handling many hospitals. With SOAP based messaging they can easily handle different systems, billing systems, medical records systems etc. Use
Microsoft-based systems.
Countrywide financial simplifies lending: IBM Websphere based SOA is used to deliver services.
Guardian Life Insurance uses SOA: IBM websphere based services. Uses
EJB for business logic.
British Telecom uses combination of BEA systems and Microsoft’s
Connected Services Framework. Billing backend and operational support for the organization are web services. Legacy systems are enabled as web services.
Amazon.com provides WS API for developers to implement applications leveraging their architecture and data.
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XML
XML is a markup language, developed by
W3C (World Wide Web Consortium), mainly to overcome the limitations of HTML.
But it took a life of its own and has become a very popular part of distributed systems.
We will examine its definition, associated specifications (DTD, XSLT etc.), Java APIs available to process XML, protocols and services based on XML, and the role XML plays in a distributed computing environment.
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First Look at XML
It has no predefined tags.
Such as in HTML
Domains may specify their own set of standard tags
It is stricter.
Most html document have errors and the browser have to built to take care of these.
On the other hand XML has a strict syntax.
There is a notion of validity and
A notion of well-formed.
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An Example: Memo
See the two documents enclosed: one in html and the other in XML formats.
Observe the meaningful tags in XML.
Compare it to a class definition: it looks like a class with data definitions and accessors (tags).
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Memo.html vs memo.xml
<!DOCTYPE html PUBLIC "-//W3C//DTD
HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
<title>memo.html</title>
</head>
<body>
<h3>Hello World</h3>
Bina<br>
CS 220 Advanced Java Programming Students
<br>
Wake up everyone<br>
BR<br>
<br>
</body>
</html>
<?xml version="1.0" ?>
<!DOCTYPE memo (View Source for full doctype...) >
<memo>
<header>Hello World</header>
<from>bina</from>
<to>CS220 Advanced Java
Programming Students</to>
<body>Wake up everyone</body>
<sign>br</sign>
</memo>
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Memo Class
Memo
Header
Body
Para[]
Link
From
To
Signature
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XML document Content
XML documents are composed of markup and contents
Some of markup tags:
Element
Attributes
Entity References
Comments
Processing instructions
CDATA sections
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Elements
Elements are the most common form of markup.
Delimited by angle brackets, most elements identify the nature of the content they surround.
Example: <allen><quote>Goodnight,
Gracie.</quote></allen>
Some elements may be empty, as seen above, in which case they have no content. If an element is not empty,it begins with a start-tag, <element>, and ends with an end-tag, </element>.
Example:<applause/>
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Attributes
Attributes are name-value pairs that occur inside start-tags after the element name. For example,
<div class="preface"> is a div element with the attribute class having the value preface.
In XML, all attribute values must be quoted.
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Entities
In XML, entities are used to represent these special characters.
Entities are also used to refer to often repeated or varying text and to include the content of external files.
Example: & to represent &
&US to represent United States
XML also has a set of predefined entities:
", &
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Comments
Comments begin with <!-- and end with
-->. Comments can contain any data except the literal string --. You can place comments between markup anywhere in your document.
Example:
<!– loosely inspired by the vcard3.0 -->
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Processing Instructions (PI)
Processing instructions (PIs) are an escape hatch to provide information to an application. Like comments, they are not textually part of the XML document, but the
XML processor is required to pass them to an application.
Processing instructions have the form:
<?name pidata?>
Example:
<?xml-stylesheet href=“simple-ie5.xsl” type=“text/xsl”?>
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CDATA
In a document, a CDATA section instructs the parser to ignore most markup characters.
<?xml version=“1.0”?>
<example>
<[CDATA[
<?xml verion=“1.0”?>
<entry> ….
</entry>]]>
</example>
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XML Processing Models
XML Input Processing
Business Logic Handling
XML Output Processing
XML input
EXTRACT
Business
Logic
XML output
WEB
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XML input Processing
1.
Processing and validating the source document
2.
Recognizing/searching for relevant information based on its location or its tagging in the source document
3.
Extracting relevant information once it has been located
4.
Mapping/binding retrieved information to business objects
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XML Processing Technologies
SAX, Simple API for XML
DOM, Document Object Model API from
W3C
XSLT, XML Style Sheets Language
Transformations from W3C
XPath, the XML Path Language from
W3C
Other third party APIs.
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Apache Ant Tool
Ant tool is an XML based build tool.
Ant requires its config files to be specified in XML format.
Config file build.xml has general commands for ant tool.
Ant tool is used for build, deploy, and run java applications.
See these tutorial for more information on ant:
Tutorial1: http://www.ii.uni.wroc.pl/~nthx/java/ant.html
Tutorial2: http://www.iseran.com/Java/ant/tutorial/ant_tutorial.html
Ant Book Chapter: http://www.oreilly.com/catalog/anttdg/chapter/ch01.pdf
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XML to SOAP
Simple xml can facilitate sending message to receive information.
The message could be operations to be performed on objects.
Simple Object Access Protocol (SOAP)
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SOAP Request
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<getProductDetails xmlns="http://warehouse.example.com/ws">
<productId>827635</productId>
</getProductDetails>
</soap:Body>
</soap:Envelope>
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SOAP Reply
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<getProductDetailsResponse xmlns="http://warehouse.example.com/ws">
<getProductDetailsResult>
<productName>Toptimate 3-Piece Set</productName>
<productId>827635</productId>
<description>3-Piece luggage set. Black Polyester.</description>
<price>96.50</price>
<inStock>true</inStock>
</getProductDetailsResult>
</getProductDetailsResponse>
</soap:Body>
</soap:Envelope>
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SOAP
Web Services (WS)
Literature surveyed:
1. IBM’s alphaworks site: http://www-106.ibm.com/developerworks/webservices/
2. http://www-3.ibm.com/software/solutions/webservices/pdf/WSCA.pdf
3. O’Reilly book on Web Services: Kim Topley’s Webservices in a
Nutshell: http://www.oreilly.com/catalog/javawsian/index.html
This link has a sample chapter (SAAJ) and zip of all examples in the book.
4. http://www.w3.org/DesignIssues/WebServices.html
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Web Services Suite of
Protocols
A suite of protocols define the Web Services
Technology.
These are used to describe, publish, discover, deliver and interact with services.
The information about the protocols is from
IBM’s developerworks .
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WS Suite of Protocols
Messaging protocol Simple Object Access Protocol
(SOAP) encodes messages so that they can be delivered over the transport protocols HTTP, SMTP or
IIOP.
Web Services Definition Language (WSDL) is used to specify the service details such as name, methods and their parameters, and the location of the service.
This facilitates the registering and discovery of the service.
For services to locate each other, the Universal
Description, Discovery and Integration (UDDI) protocol defines a registry and associated protocols for locating and accessing services.
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WS Suite of Protocols (contd.)
The WS-Transaction and WS-Coordination protocols work together to handle distributed transactions.
The Business Process Execution Language for Web
Services (BPEL4WS) defines workflow operations.
WS-Security is a family of protocols that cover authentication, authorization, federated security, secure communications, and delivery.
WS-Policy is another group of protocols that define the policy rules behind how and when Web services can interact with each other.
WS-Trust defines how trust models work between different services.
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WS Stack
WSFL Service Flow
UDDI Service Discovery
UDDI Service Publication
WSDL
Service Description
SOAP
HTTP, FTP, MQ
XML-based Messaging
Network
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WS Interoperability Infrastructure
WSDL Service Description
XML Messaging SOAP
HTTP Network
Do you see any platform or language dependencies here?
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JAX-RPC
JAX-RPC: Java API for XML-based Remote Procedure
Call (RPC).
An API for building Web Services and Web Services clients.
Some important concepts in JAX-RPC are:
Type-mapping system (WSDL to Java)
Service endpoint
Exception handling
Service endpoint context
Message handlers
Service clients and service context
SOAP with attachments
Runtime services
JAX-RPC client invocation models
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JAX-RPC (contd.)
JAX-RPC is designed to provide a simple way for developers to create Web services server and Web services client.
Based on remote procedure calls; so the programming model is familiar to Java developers who have used RMI or CORBA.
Major difference between RMI and JAX-RPC is that messages exchanged are encoded in XML based protocol and can be carried over a variety of transport protocols such as HTTP, SMTP etc.
You can use JAX-RPC without having to be an expert in XML, SOAP, or HTTP.
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The JAX-RPC Programming
Model
Services, ports and bindings
JAX-RPC web service servers and clients
JAX-RPC service creation
JAX-RPC client and server programming environments
Stubs and ties
Client invocation modes
Static and dynamic stubs and invocation
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Services, ports and bindings
Service endpoint interface or service endpoint that defines one or more operations that the web service offers.
Access to an endpoint is provided by binding it to a protocol stack through a port .
A port has an address that the client can use to communicate with the service and invoke its operations.
An endpoint can be bound to different ports each offering a different suite of protocols for interaction.
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Endpoint, Port and binding
Web service endpoint
Port1 port2 port3
SOAP1.1
Over http
SOAP 1.1 over https
Other. Ex: ebXML over
SMTP
Web services Client https 1.1 transport soap1.1 messages
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WS Development Lifecycle
Build:
Definition of service interface
Definition of service implementation
New services
Existing application into WS
Composing a WS out of other WS and applications
Source compiled and Stubs and Ties are generated.
Deploy:
Publication of the service interface and service implementation to service registry or service requestor.
Deployment of executables in an execution environment.
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WS Development Lifecycle
(contd.)
Run: A WS is available for invocation.
Requestor can perform find and bind operation.
Manage: on going management and administration for security, availability, performance, QoS, and business processes.
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Service Oriented Architectures
Lets look at some success stories.
Amazon.com has is data collection available web services developers.
See these URLs:
Amazon.com E-Commerce Service ( ECS )
Conceptual Model
ECS Usage/Query Scenarios
Types of data available through ECS (and not available)
Sample applications (some of them are cool )
Programming and API for making (SOAP) requests
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Summary
We looked at foundational concepts supporting web services: XML, SOAP,
WSDL and Web Services standards.
We also illustrated the concepts using sample programs.
Best way to get started is try out WS tutorials by yourself.
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