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

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 a 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). 6/1/2019

Web services (contd.) Is platform, language and operating system independent It works on a two-way Secure socket layer (SSL) It operates on the well-established HTTP protocol Open Grid Services Infrastructure (OGSI) is also web services based Is the basis for Software as a Service (Saas), Infrastructure as a Service (IaaS), and Platform as a Service (PaaS)– simply put the “Cloud computing” 6/1/2019

Web Services (WS): Technically Characteristics (Ch.19) A WS interface consists of a collection of operations that can be used by the client over the internet. A web service has a URI (Uniform Resource Identifier) Web services are accessed by URIs by clients using messages formatted in XML. SOAP is used to express Request and Reply messages in XML and to transport them over HTTP. ( We will discuss REST later) A web service consists of a single remote object – it is not possible to instantiate additional remote objects during the running of a web service and remote object references are not used. -- DGC and remote references are irrelevant. XML security mechanisms can be used. How the task is accomplished is up to the server once the message arrives from the client: total transparency WSDL provides additional details than for standard operation: for encoding, security, communication and location. 6/1/2019

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. 6/1/2019

Endpoint, Port and binding Web service endpoint Port1 port2 port3 Web services Client REST over http SOAP1.1 Over http SOAP 1.1 over https Other. Ex: ebXML over SMTP https 1.1 transport messages 6/1/2019

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. 6/1/2019

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. 6/1/2019

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. 6/1/2019

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 + ".";   } } 6/1/2019

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="http://localhost:8080/helloservice/hello?wsdl") 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); 6/1/2019

Development using an IDE An IDE supports tools for compilation, deployment, automatic generation of proxies, auto completion, auto import of packages, build tool etc. 6/1/2019

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 6/1/2019

WS Interoperability Infrastructure Service Description WSDL XML Messaging SOAP Network HTTP 6/1/2019

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 Email, IIOP Network 6/1/2019

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 http://www.w3.org/TR/wsdl#_wsdl http://www.w3schools.com/wsdl/wsdl_documents.asp http://webservices.amazon.com/AWSECommerceService/AWSECommerceService.wsdl? Lets look at the components of WSDL and look at Amazon.com ECS as example 6/1/2019

Anatomy of a WSDL document 6/1/2019

Sample WSDL http://www.w3.org/2001/04/wsws-proceedings/uche/wsdl.html http://webservices.amazon.com/AWSECommerceService/AWSECommerceService.wsdl? 6/1/2019

Demo: Develop, deploy and consume a sample WS We will use Netbeans IDE to understand WS ecosystem and designing, building, deploying and consuming a WS. http://netbeans.org/kb/trails/web.html http://netbeans.org/kb/docs/websvc/jax-ws.html 6/1/2019