1. Distributed System using Web Services
B. Ramamurthy
4/6/2019

2. Web Services
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 messaging.
Web services enable program integration across application and organizational boundaries.
Deployable unit.
A Web service uses protocol to describe an operation and the data exchange with another web service. Ex: SOAP
Platform independent, say, through WSDL.
Publishable, discoverable, searchable, queryable
Scalability issues: A group of web services collaborating accomplish the tasks of a large-scale application. The architecture of such an application is called Service-Oriented Architecture (SOA).
4/6/2019

3. Web Services (Colouris)
A web service provides a service interface enabling clients to interact with servers in a more general way than web browsers do.
Clients access operations in the interface usually by XML messages over http.
However other architectural models such as REST and CORBA could access WS.
WSDL provides additional details than for standard operation: for encoding, security, communication and location.
4/6/2019

4. Services, ports and bindings
Service endpoint interface (SEI) 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.
4/6/2019

5. Endpoint, Port and binding
Web service
endpoint
Port port port3
Web services Client
SOAP1.1
Over http
SOAP 1.1 over
https
Other. Ex:
ebXML over
SMTP
https 1.1 transport
soap1.1 messages
4/6/2019

6. WS Lifecycle Build: Deploy: 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.
4/6/2019

7. WS 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.
4/6/2019

8. Creation and consumption of WS
Based on Sun’s WS discussion.
The starting point for developing a JAX-WS web service is a Java class annotated with the javax.jws.WebService annotation. The WebService annotation defines the class as a web service endpoint. A WS method can also be created using annotation.
4/6/2019

9. Coding WS Hello Server package helloservice.endpoint;
import javax.jws.WebService;
@WebService() public class Hello {   
private String message = new String("Hello, ");   
public void Hello() {}   
@WebMethod()   
public String sayHello(String name) {     
return message + name + ".";   } }
4/6/2019

10. Coding the Hello WS client
Uses the javax.xml.ws.WebServiceRef annotation to declare a reference to a web service. WebServiceRef uses the wsdlLocation element to specify the URI of the deployed service's WSDL file.
@WebServiceRef(wsdlLocation=" static HelloService service;
Retrieves a proxy to the service, also known as a port, by invoking getHelloPort on the service.
Hello port = service.getHelloPort();
The port implements the SEI defined by the service.
Invokes the port's sayHello method, passing to the service a name.
String response = port.sayHello(name);
4/6/2019

11. Development using an IDE
An IDE supports tools for compilation, deployment, automatic generation of proxies, auto completion, auto import of packages, build tool etc.
4/6/2019

12. Application Architecture
Weather Client
JAX-WS Stub
JAX-WS
Runtime (APIs)
Transport
Weather Service
Endpoint impl
JAX-WS Ties
JAX-WS
Runtime (APIs)
Transport
SOAP/HTTP
4/6/2019

13. WS Interoperability Infrastructure
Service Description
WSDL
XML Messaging
SOAP
Network
HTTP
4/6/2019

14. WS Stack Service Flow WSFL Service Discovery UDDI Quality of Service
Security
Management
Quality of Service
Service Discovery
UDDI
Service Publication
UDDI
Service Description
WSDL
XML-based Messaging
SOAP
HTTP, FTP, MQ
, IIOP
Network
4/6/2019

15. WSDL
Web Services Definition Language for definition of WS in a standard format and for publication to allow discovery by computational agents.
Lets understand WSDL
Lets look at the components of WSDL and look at Amazon.com ECS as example
4/6/2019

16. Anatomy of a WSDL document
4/6/2019

17. Sample WSDL http://www.w3.org/2001/04/wsws-proceedings/uche/wsdl.html
4/6/2019

18. Demo: Develop, deploy and consume a sample WS
We will use Netbeans IDE (any version above 5.5 should be fine).
4/6/2019