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SOA(Service-Oriented Architecture)

SOA is a software architecture that facilitates the loosely-coupled integration between diverse applications.
It provides the flexibility to make changes in a software and its networking components, without affecting other existing components of the system.
SOA is represented as a collection of services communicating with each other. A service is a well-defined business functionality.
SOA consists of some entities that maximize the loose coupling and reusability:

  • Service registry
  • Service provider
  • Service consumer

Web Services

The concept of SOA is implemented using Web services.
A Web service is an application function that performs a specific task or set of tasks.
At the same time, the Web services can be published, located, or invoked over a network.

Benefits

  • Support for application and data integration
  • Versatility
  • Code reuse
  • Cost savings

JWSDP toolkit

Web services are developed using JWSDP toolkit.
This toolkit enables developers to build, test, and deploy the XML applications, Web applications, and Web services in Java.

APIs description Usage
JAX-WS Java API for XML Web Services used for developing the XML-based Web services.
JAXP Java API for XML Processing used for processing the XML data from the Java applications.
JAXB Java Architecture API for XML Binding allows you to map the XML document to the Java objects, and vice versa.
SAAJ SOAP with Attachments API for Java used to transport large files as attachments with SOAP messages over the Internet.
JAXR Java API for XML Registries used to access different Web services registries.

Types of Web Services

Web services can be developed using two different approaches:

  • XML-based Web services
  • RESTful Web services

XML-based Web services

An XML-based Web service is a self-describing Web component that exposes its functionality to the consumers.

Components:

name description
WSDL An XML-based document used to describe the functionalities of an XML-based Web service.
UDDI An XML-based directory service used to register an XML-based Web service.
SOAP An XML-based protocol used to exchange information between applications. It used the HTTP protocol for data transfer.

webservice

WSDL(Web Service Definition Language)

WSDL is an XML-based file that describes details such as publicly available functions of the Web service, location of a Web service, and the data type of messages exchanged between Web services.

Elements
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<definitions>
<types>
<message>
<portType>
<binding>
<service>
Types of WSDL Models
  • Abstract model
    • contains <types>, <message>, <portType>
  • Concrete model
    • contains <binding>, <service>

UDDI(Universal Description Discovery and Integration)

UDDI is an XML-based directory service that shares details about the Web services globally.

Components
  • Yello Pages
  • White Pages
  • Green Pages

SOAP

(Simple Object Access Protocol)

Elements
  • SOAP envelope
  • SOAP header
  • SOAP body
  • SOAP fault

[DEMO]

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POST /endpoint.pl HTTP/1.1
Content-Type: text/xml
Content-Length: 167
SOAPAction: urn: example-org: demos#Method
<s:Envelope xmlns:s='HTTP://schemas.xmlsoap.org/soap/envelope/'>
<s:Body>
<m:Method xmlns:m='urn:example-org:demos' />
</s:Body>
</s:Envelope>

Building a Web Service

1.Creating a Web Service

JAX-WS is an API used for creating Web services that communicate with clients using XML.
The JAX-WS API is defined in the javax.xml.ws package.

Annotation Description
@WebService defines the class as an implementing class a Web service interface
@WebMethod defines that the method is a Web service method; supported only by those classed that have a @WebService annotation
@OneWay defines that the Web method has input but no output; can be specified only for methods that does not have a return type
@WebParam defines the parameters of methods used in a Web service
@WebServiceRef defines a reference to a Web service

2.Defining the Web Methods

[Demo]

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package com.helloservice;

import javax.jws.WebMethod;
import javax.jws.WebParam;
import javax.jws.WebService;

@WebService()

public class Hello{

@WebMethod

public String hello(@WebParam(name="name")String name){
	return "Hello"+name+"!";
}
}

RESTful Web services

The RESTful Web services are the services built on the REST architectural style.

REST

REST is a softaware style architecture based on SOA which is used for designing RESTful Web services.

  • REST is NOT a standard architecture style. REST follows the resource-oriented architecture.
  • REST is NOT a replacement for XML-based Web services. They are used for different businiess requirements.
  • While XML-based Web approach defines new specifications for Web application development, the REST approach uses the existing Web standards for developing Web services.
  • REST is mostly preferred over XML-based Web services because of its lightweight nature and simple design.
REST Design Principle
  • Using HTTP methods
  • Exhibiting stateless nature
  • Exposing directory structure
  • Transferring data in XML and JSON formats

Implementing RESTful Web Services

JAX-RS API

The javax.ws.rs package

Annotation Description
@ApplicationPath Indentify the app path
@Consumes defines the MIME types that are accepted by the methods of a resource class
@DELETE -
@GET -
@HEAD -
@HeaderParam binds the values of an HTTP header to the parameter of a resource method, resource class fields, or resource class bean property
@HttpMethod -
@Path Indentify the URI path
@POST -
@Produces defines the MIME types that the methods of a resource class or MessageBoxWriter interface can produce
@PUT -
QueryParam binds the values of an HTTP query parameter to a resource method, resource class fields, or resource class bean property