1. 168493 XML and Web Services (II/2546)
Kanda Runapongsa
Dept. of Computer Engineering
Khon Kaen University
Dept. of Computer Engineering, Khon Kaen U.

2. 168493: XML and Web Services (II/2546)
Overview
Introduction to Web Services
Web Services Standards
Java Support for Web Services
Apache Axis
Installing Apache Axis
Invoking a service
Deploying a service
168493: XML and Web Services (II/2546)

3. 168493 XML and Web Services (II/2546)
Web Services -- Basics
Expose services to other processes
Internet or intranet
Black boxes
Component-like, reusable
Do not know how the service is implemented
Based on open standards
HTTP, XML, and SOAP
Today there is a strong desire for easy-to-use and easy-to-create Web applications, and those applications are required to be language and platform independent.
Web Services expose their functionality via standard Web protocols, like HTTP and XML, and enable you to interconnect Web applications. Broadly speaking, Web Services are URL-addressable resources that return requested information to a client or manipulate the data model behind the Web Service.
Black boxes
Like components, Web Services are black boxes and can be reused without knowledge about how the service is implemented.
Based on open standards
Web Services are based on open standards like HTTP, XML, and SOAP. So any application that supports these standards is able to support Web Services.
168493: XML and Web Services (II/2546)
Dept. of Computer Engineering, Khon Kaen U.

4. 168493 XML and Web Services (II/2546)
Web Services -- Basics
Interconnect
Applications
Different clients
Many devices
Distribution and integration of application logic
Web Services are loosely coupled
Enable the programmable Web
Not just purely interactive Web
Interconnect
With Web Services, you can easily connect applications – even via the Internet.
Different clients can make use of Web Services. For example, a browser can make use of the functionality the service offers. Also Web Services themselves can communicate with each other or just call methods that are provided by other Web Services.
And many different devices can consume Web Services. For example, a WAP device such as a mobile phone can invoke a Web Service.
Distribution and integration of application logic
A significant advantage of Web Services is that developers can program against a Web Service to import its functionality into their own Web Service to import its functionality into their own Web applications. We now have the technology to not only distribute application logic, but also to integrate functionality that is provided by a ‘service’ that resides ‘somewhere out there’
Web Services are loosely coupled
Because Web Services are loosely coupled, you can change the implementation of a service without affecting the connected partner. The basic principle to achieve this is a homogeneous infrastructure that meets two requirements:
First, we need underlying protocols that are common to all communicating entities. This is covered because Web Services are based on the aforementioned open standards. One important point to stress is that XML plays a major role here.
Second, we need to ensure that communication takes place asynchronously through messages.
Enable the “programmable Web”
Because of these characteristics, Web Services enable the programmable Web. We are no longer restricted to a purely interactive Web.
168493: XML and Web Services (II/2546)
Dept. of Computer Engineering, Khon Kaen U.

5. 168493: XML and Web Services (II/2546)
Web Services -- Basics
What is a ‘Web Service’?
‘Web’ accessible
Usually implies accessible via HTTP
Service architecture
Request/response
XML data transfer
Many serious Web services in use for years
Custom XML formats specific for each service
168493: XML and Web Services (II/2546)

6. Web Services -- Examples
XML and Web Services (II/2546)
Web Services -- Examples
A Stock quote service
The request asks for the current price of a specified stock
The response gives the stock price
A service that maps out an efficient route for the delivery of goods
A business sends a request containing the delivery destinations
The response returns the most cost-effective delivery route
Web services, in the general meaning of the term, are services offered via the Web. In a typical Web services scenario, a business application sends a request to a service at a given URL using the SOAP protocol over HTTP. The service receives the request, process it, and returns a response. An often-cited example of a Web service is that of a stock quote service, in which the request asks for the current price of a specified stock, and the response gives the stock price. This is one of the simplest forms of a Web service in that the request is filled almost immediately, with the request and response being parts of the same method call.
Another example could be a service that maps out an efficient route for the delivery of goods. In this case, a business sends a request containing the delivery destinations, which the service processes to determine the most cost-effective delivery route.
168493: XML and Web Services (II/2546)
Dept. of Computer Engineering, Khon Kaen U.

7. Web Services -- Examples
XML and Web Services (II/2546)
Web Services -- Examples
Web services and consumers of Web services are typically businesses, making Web services predominantly business-to-business (B2B) transactions
An enterprise can be the provider of Web services and also the consumer of other Web services
Web services and consumers of Web services are typically businesses, making Web services predominantly business-to-business (B2B) transactions. An enterprise can be the provider of Web services and also the consumer of other Web services. For example, a wholesale distributor of rices could be the consumer role when it uses a Web services to check on the availability of rices and in the provider role when it supplies prospective customers with different vendor’s prices for rices.
168493: XML and Web Services (II/2546)
Dept. of Computer Engineering, Khon Kaen U.

8. Web Services Interaction Diagram
UDDI
Registry 1
Request WSDL location 2
Download WSDL
WSDL
Send SOAP messages
With XML documents
Web
Services 3
168493: XML and Web Services (II/2546)

9. Web Services Infrastructure
Language and platform independent infrastructure for
loosely-coupled, inter-operable
App2app communication over the Internet
168493: XML and Web Services (II/2546)

10. Web Services Infrastructure
Language and platform independent
Separation of specification and implementation
Loosely coupled
Message based, synchronous and asynchronous interactions
168493: XML and Web Services (II/2546)

11. Web Services Infrastructure
Over the Internet
No centralized control, use of established protocols, security considerations
Inter-operable
Standards based
168493: XML and Web Services (II/2546)

12. Early (Internet) Technologies
SMTP/MINE: Protocols of
FTP, NNTP
HTTP/HTTPs, HTML
The protocols behind the Internet’s popularity
Most of these facilitated application to human interaction over the Internet/intranet
168493: XML and Web Services (II/2546)

13. Early (Intranet) Technologies
XML and Web Services (II/2546)
Early (Intranet) Technologies
Distributed object model
Components: packaging and interoperability
Remoting: remote method invocation
COM/DCOM from Microsoft, CORBA,
Java RMI and EJBs
If we are talked about distributed computing, we are talking about the client/server model. Today this term implicitly means three-tier architecture, where we have:
First tier: user interface
Second tier: business logic
Third tier: database
Normally each of these tiers resides on a dedicated machine. The first tier is on a client, which could be a browser. The second tier is on a server, in this case the Web server. The last tier could be, for example, a Microsoft SQL Server database.
Distributed computing requires distributed object model or remoting architecture. With this you can develop distributed applications as you did with a local programming model, and even call services on remote systems. This is called remoted method invocation.
Besides this we need the ability to interchange services – or components. Components are black boxes offering services or functionalities, and they provide for packaging and interoperability.
The most import object models today are:
COM: Component Object Model
CORBA: Common Object Request Broker Architecture
Java RMI and EJB: Java Remote Method Invocation and Enterprise JavaBeans.
168493: XML and Web Services (II/2546)
Dept. of Computer Engineering, Khon Kaen U.

14. 168493 XML and Web Services (II/2546)
What’s Wrong with That?
Limited COM support on non-Windows platforms
COBRA: Server object implementation not portable
Most of these facilitated app2app within a trusted intranet and without much consideration to interoperability across different implementations
Object models like COM, COBRA, and RMI tightly couple a service and the consumer of this service. This is a reason for the need of a homogeneous infrastructure. But there’s no guarantee that the service and the consumer use the same operating system, programming language, or object model. Another problem arises with versioning: if the implementation changes on one side, the other side will fail.
Limited COM support on non-Windows platforms
While COM is widely supported on the Windows platform, the support on non-Windows platforms like UNIX is limited. The usage of COM within Java requires the Microsoft Java Virtual Machines. This is really an issue, because Microsoft JVM is not supported on non-Windows platforms.
From the beginning COBRA was designed to target the problem of inter-machine communication, providing for cross-language and cross-platform interoperability. However, since COBRA is a specification – not a product – implementation of COBRA are vendor specific. So, if you make use of vendor-specific features or services, your applications may not be portable.
With Enterprise JavaBeans, you are tied to one language: Java
168493: XML and Web Services (II/2546)
Dept. of Computer Engineering, Khon Kaen U.

15. App2App Interaction – the Web Services Way
Transport protocol
HTTP/HTTPS
Data encoding
SOAP (Simple Object Access Protocol)
XML Schema
Interface Description
WSDL (Web Services Description Language)
168493: XML and Web Services (II/2546)

16. The Web Services Way (Cont)
Service Description and Discovery
UDDI (Universal Description, Discovery and Integration)
Security
WS-Security, XML-Signature, XML-Encryption
168493: XML and Web Services (II/2546)

17. 168493: XML and Web Services (II/2546)
What is SOAP?
Simple Object Access Protocol
It defines a standard packaging format for transmitting XML data between applications on a network
Usually request-response structure
Transport normally HTTP, but can be anything (SMTP, etc.)
168493: XML and Web Services (II/2546)

18. 168493: XML and Web Services (II/2546)
A SOAP Message
A SOAP message is just an XML document
The message might be sent from one application to another to synchronize contact information on two different systems
SOAP takes advantages of XML namespaces and XML schemas
168493: XML and Web Services (II/2546)

19. SOAP Message Structure
Envelope is wrapper for content, but no useful information
Optional header can contain control information
Body contains actual data in XML encoding
Attachments can hold other types of data (binary, etc.)
SOAP Envelope:
Top-level wrapper
SOAP Header
(Optional):
Extension information
SOAP Body:
Application data
168493: XML and Web Services (II/2546)

20. 168493: XML and Web Services (II/2546)
A SOAP Message Example
<?xml version=“1.0” encoding=“UTF-8”?>
<soap:Envelope
xmlns:soap=“
xmlns:addr=“
168493: XML and Web Services (II/2546)

21. 168493: XML and Web Services (II/2546)
A Soap Message Example
<soap:Body>
<addr:address> <addr:name>Amazon.com</addr:name>
<addr:zip>90952</addr:zip>
</addr:address>
</soap:Body>
</soap:Envelope>
168493: XML and Web Services (II/2546)

22. 168493: XML and Web Services (II/2546)
WSDL
Web Services Description Language
A standard for describing the structure of the XML data exchanged between two systems using SOAP
When you create a new Web service, you can also create a WSDL document that describes about the type of data we are exchanging
168493: XML and Web Services (II/2546)

23. WSDL 1.1 Document Structure
A WSDL document describes
What the service can do
Where it resides
How to invoke it
WSDL descriptions can be made available from an UDDI registry
Types
Messages
Port Types
Bindings
Services
168493: XML and Web Services (II/2546)

24. 168493: XML and Web Services (II/2546)
Why Do We Need UDDI?
Universal Description, Discovery, and Integration
We still need a guidance to find the WSDL documents
UDDI can help others find our Web services easily and use them to communicate with our Web services
168493: XML and Web Services (II/2546)

25. 168493: XML and Web Services (II/2546)
What is UDDI?
UDDI defines a standard set of Web service operations that are used to store and look up information about other Web service applications
UDDI defines a standard SOAP-based interface for a Web services registry
A UDDI is often referred to as a “Yellow Pages” for Web services
168493: XML and Web Services (II/2546)

26. 168493: XML and Web Services (II/2546)
Java APIs for XML
Java API for XML Processing (JAXP) – Process XML documents using various parsers
Java API for XML-based RPC (JAX-RPC) – sends SOAP method calls
Java API for XML Registries (JAXR) – provides a standard way to access
168493: XML and Web Services (II/2546)

27. 168493: XML and Web Services (II/2546)
Apache Axis
Apache Axis is a toolkit to create and consume Web Services for the Java platform which can be downloaded from
Axis 1.1 supports numerous Java technologies
SAAJ (SOAP with Attachments API for XML)
JAX-RPC (Java API for XML based Remote Procedure Call)
168493: XML and Web Services (II/2546)

28. 168493: XML and Web Services (II/2546)
Apache Axis
A simple stand-alone server
A server which plugs into servlet engines such as Tomcat
Extensive support for the Web Service Description Language (WSDL)
Emitter tooling that generates Java classes from WSDL
A tool for monitoring TCP/IP packets
168493: XML and Web Services (II/2546)

29. Apache Axis – Web Service
Create an object that has methods and publish it on the Internet
You can access your Web service just like if it was a local object through a protocol called SOAP
All the operations of a Web service are expressed through a WSDL
The WSDL file is used to access and call operations on Web services
168493: XML and Web Services (II/2546)

30. 168493: XML and Web Services (II/2546)
Concepts: SOAP & AXIS
Apache Axis is an Open Source SOAP server and client
SOAP is a mechanism for inter-application communication between systems written in arbitrary languages, across the Internet
168493: XML and Web Services (II/2546)

31. 168493: XML and Web Services (II/2546)
Concepts: SOAP & AXIS
SOAP usually exchanges messages over HTTP
The client POSTs a SOAP request
The client then receives either
An HTTP success code and a SOAP response
Or an HTTP error code
Open Source means that you get the source, but there is no formal support
168493: XML and Web Services (II/2546)

32. 168493: XML and Web Services (II/2546)
Concepts: SOAP & AXIS
SOAP messages are XML messages
These messages exchange structured information between SOAP systems
Messages consist of one or more SOAP elements inside an envelope, Headers, and the SOAP Body
168493: XML and Web Services (II/2546)

33. 168493: XML and Web Services (II/2546)
Concepts: SOAP & AXIS
Axis handles the magic of converting Java objects to SOAP data when it sends it over the wire or receive results
SOAP Faults are sent by the server when something goes wrong; Axis converts these to Java exceptions
168493: XML and Web Services (II/2546)

34. 168493: XML and Web Services (II/2546)
Concepts: SOAP & AXIS
Axis implements the JAX-RPC API, one of the standard ways to program Java services
Axis is compiled in the JAR file axis.jar; it implements the JAX-RPC API declared in the JAR files jaxrpc.jar and saaj.jar
168493: XML and Web Services (II/2546)

35. 168493: XML and Web Services (II/2546)
References
Web Services with JAX-RPC and Axis
168493: XML and Web Services (II/2546)