WebServices in Java

What are Web Services?

a piece of business logic, located somewhere on the Internet, that is accessible through standard-based Internet protocols such as HTTP or SMTP

Characteristics

XML based

Loosely Coupled

Coarse grained

Ability to be Synchronous or Asynchronous

Supports Remote Procedure Calls (RPCs)

Supports document exchange



Major Web Services Technologies


Simple Object Access Protocol (SOAP)

Web Service Description Language (WSDL)

Universal Description, Discovery, and Integration (UDDI)

Simple web service interaction



Why Java Web Services

Ability of enterprises using different computing platforms to communicate with each other

Java ensures code portability

J2EE ensures scalability

APIs hide all the implementation details

Components are reusable

Development time is substantially reduced

Java Web Service Developer Pack

Free integrated toolkit that allows Java developers to build, test and deploy Web services

Web services standards WSDL, SOAP, UDDI

APIs provided

Java API for XML Messaging (JAXM)

Java API for XML Registries (JAXR)  Java API for XML-based RPC (JAX-RPC)


Sample Scenario-Online Book store









JAX-RPC API for XML based RPC



RPC-based Web service is a collection of procedures that can be called by a remote client

Ties, the low-level classes that the server needs to communicate with a remote client

WSDL document used for creating stubs, the low-level classes that are needed by a client to communicate with a remote service.

Stubs can be static or dynamic.

Tools wscompile and wsdeploy

simplify our job




Service consists of

Interface:

Declares the service's remote procedures

Implementation class:

Implements the remote procedures.



Configuration files jaxrpc-ri.xml and web.xml contain all the parameters needed to deploy the service.



Client is a Java program which uses the stubs created from the WSDL document of the service

Configuration file config.xml contains the location of the WSDL document.

Service Interface

public interface BookIF {

public Book getPriceList();

public String orderBook(String BookName, int quantity);

}



Implementation class

public class BookImpl implements BookIF {

public Book getPriceList() { . . . }

public String orderBook(String BookName, int quantity) { . . . }

}



Client code



public class BookClient {

public static void main(String[] args) {

BookIF BookOrder = new BookServiceImpl().getBookIF();

Book priceList = BookOrder.getPriceList():

for (int i = 0; i <>JAXM API for XML Messaging



Provides a standard way to send XML documents over the Internet

Based on SOAP and SOAP with Attachments specifications

Messaging provider service, which does the behind-the-scenes work required to transport and route messages

Standalone client also possible for request-response type of messaging

Very useful when Enterprise work on shared schemas.(e.g.. Schema for order form in Online Book Store)



Advantages over JAX-RPC

One-way (asynchronous) messaging

Routing of a message to more than one party

Reliable messaging with guaranteed delivery



Steps

1.Setting up Connection with the end-point.

2.Creating the SOAP message and populate it.

3.Sending the message.



JAXR API for XML Registries



Provides a convenient way to

access standard business registries

Supports two standards ebXML and UDDI

Standards groups have developed

schemas for particular kinds of XML documents, and two businesses might for example, agree to use the schema which is stored in the registry.

Querying a registry-Useful methods

1.findOrganizations

which returns a list of organizations that meet the specified criteria

2.findServices

which returns a set of services offered by a specified organization

3. findServiceBindings

which returns the service bindings (information about how to access the service) that are supported by a specified service



Similar methods exist for Managing Registry Data.