RMI Java Interview Questions – Set 02

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What is the difference between SOA and a Web service

SOA is a software design principle and an architectural pattern for implementing loosely coupled, reusable and coarse grained services. You can implement SOA using any protocols such as HTTP, HTTPS, JMS, SMTP, RMI, IIOP (i.e. EJB uses IIOP), RPC etc. Messages can be in XML or Data Transfer Objects (DTOs).

Web service is an implementation technology and one of the ways to implement SOA. You can build SOA basedapplications without using Web services – for example by using other traditional technologies like Java RMI, EJB, JMS based messaging, etc. But what Web services offer is the standards based  and platform-independent service via HTTP, XML, SOAP, WSDL and UDDI, thus allowing interoperability between heterogeneous technologies such as J2EE and .NET.

What are the different application integration styles

There are a number of different integration styles like

  • Shared database
  • batch file transfer
  • Invoking remote procedures (RPC)
  • Exchanging asynchronous messages over a message oriented middle-ware (MOM).

Web services when you can use traditional style middle-ware such as RPC, CORBA, RMI and DCOM

The traditional middle-wares tightly couple connections to the applications and it can break if you make any modification to your application. Tightly coupled applications are hard to maintain and less reusable. Generally do not support heterogeneity. Do not work across Internet. Can be more expensive and hard to use.

Web Services support loosely coupled connections. The interface of the Web service provides a layer of abstraction between the client and the server. The loosely coupled applications reduce the cost of maintenance and increases re-usability. Web Services present a new form of middle-ware based on XML and Web. Web services are language andplatform independent. You can develop a Web service using any language and deploy it on to any platform, from small device to the largest supercomputer. Web service uses language neutral protocols such as HTTP and communicates between disparate applications by passing XML messages to each other via a Web API. Do work across internet, less expensive and easier to use.

What are the differences between both SOAP WS and RESTful WS

  • The SOAP WS supports both remote procedure call (i.e. RPC) and message oriented middle-ware (MOM) integration styles. The Restful Web Service supports only RPC integration style.
  • The SOAP WS is transport protocol neutral. Supports multiple protocols like HTTP(S), Messaging, TCP, UDP SMTP, etc. The REST is transport protocol specific. Supports only HTTP or HTTPS protocols.
  • The SOAP WS permits only XML data format.You define operations, which tunnels through the POST. The focus is on accessing the named operations and exposing the application logic as a service. The REST permits multiple data formats like XML, JSON data, text, HTML, etc. Any browser can be used because the REST approach uses the standard GET, PUT, POST, and DELETE Web operations. The focus is on accessing the named resources and exposing the data as a service. REST has AJAX support.
  • It can use the XMLHttpRequest object. Good for stateless CRUD (Create, Read, Update, and Delete) operations.
  1. GET – represent()
  2. POST – acceptRepresention()
  3. PUT – storeRepresention()
  4. DELETE – removeRepresention()
  • SOAP based reads cannot be cached. REST based reads can be cached. Performs and scales better.
  • SOAP WS supports both SSL security and WS-security, which adds some enterprise security features like maintaining security right up to the point where it is needed, maintaining identities through intermediaries and not just point to point SSL only, securing different parts of the message with different security algorithms, etc. The REST supports only point-to-point SSL security. The SSL encrypts the whole message, whether all of it is sensitive or not.
  • The SOAP has comprehensive support for both ACID based transaction management  for short-lived transactions and compensation based transaction management for long-running transactions. It also supports two-phase commit across distributed resources. The REST supports transactions, but it  is neither ACID compliant nor can provide two phase commit across distributed transactional resources as it is limited by its HTTP protocol.
  • The SOAP has success or retry logic built in and provides end-to-end reliability even through SOAPintermediaries. REST does not have a standard messaging system, and expects clients invoking the service to deal with communication failures by retrying.