12c SOA - Rest vs SOAP WebServices

SOAP(Simple Object Access Protocol):

• SOAP is a protocol. SOAP was designed with a specification. It includes a WSDL file which has the required information on what the web service does in addition to the location of the web service.
• SOAP relies exclusively on XML to provide messaging services. Microsoft originally developed SOAP to take the place of older technologies that don’t work well on the Internet such as the Distributed Component Object Model (DCOM) and Common Object Request Broker Architecture (CORBA).
• SOAP cannot make use of REST since SOAP is a protocol and REST is an architectural pattern.
• SOAP uses service interfaces to expose its functionality to client applications. In SOAP, the WSDL file provides the client with the necessary information which can be used to understand what services the web service can offer.
• SOAP requires more bandwidth for its usage. Since SOAP Messages contain a lot of information inside of it, the amount of data transfer using SOAP is generally a lot.

          <?xml version="1.0"?>

         <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://www.w3.org/2001/12/soap-envelope" 

SOAP-ENV:encodingStyle=" http://www.w3.org/2001/12/soap-encoding">

          <soap:Body>

         <EmployeeID>int</EmployeeID>
         ......

       </soap:Body>

      </SOAP-ENV:Envelope>

REST(Representational State Transfer):

• REST is an Architectural style in which a web service can only be treated as a RESTful service if it follows the constraints of being

          Client Server
          Stateless
          Cacheable
          Layered System
          Uniform Interface

• REST can make use of SOAP as the underlying protocol for web services, because in the end it is just an architectural pattern.
• REST use Uniform Service locators to access to the components on the hardware device. For example, if there is an object which represents the data of an employee hosted on a URL as http://demo.guru99 , the below are some of URI that can exist to access them

         http://demo.guru99.com/Employee
         http://demo.guru99.com/Employee/1

• REST does not need much bandwidth when requests are sent to the server. REST messages mostly just consist of JSON messages. Below is an example of a JSON message passed to a web server. You can see that the size of the message is comparatively smaller to SOAP.

          {"city":"Mumbai","state":"Maharastra"}

• REST permits different data format such as Plain text, HTML, XML, JSON, etc. But the most preferred format for transferring data is JSON.

When to use REST and when to use SOAP

REST services should be used in the following instances

Limited resources and bandwidth – Since SOAP messages are heavier in content and consume a far greater bandwidth, REST should be used in instances where network bandwidth is a constraint.

Statelessness – If there is no need to maintain a state of information from one request to another then REST should be used. If you need a proper information flow wherein some information from one request needs to flow into another then SOAP is more suited for that purpose. We can take the example of any online purchasing site. These sites normally need the user first to add items which need to be purchased to a cart. All of the cart items are then transferred to the payment page in order to complete the purchase. This is an example of an application which needs the state feature. The state of the cart items needs to be transferred to the payment page for further processing.

Caching – If there is a need to cache a lot of requests then REST is the perfect solution. At times, clients could request for the same resource multiple times. This can increase the number of requests which are sent to the server. By implementing a cache, the most frequent queries results can be stored in an intermediate location. So whenever the client requests for a resource, it will first check the cache. If the resources exist then, it will not proceed to the server. So caching can help in minimizing the amount of trips which are made to the web server.

Ease of coding – Coding REST Services and subsequent implementation is far easier than SOAP. So if a quick win solution is required for web services, then REST is the way to go.

SOAP should be used in the following instances

Asynchronous processing and subsequent invocation – if there is a requirement that the client needs a guaranteed level of reliability and security then the new SOAP standard of SOAP 1.2 provides a lot of additional features, especially when it comes to security.

A Formal means of communication – if both the client and server have an agreement on the exchange format then SOAP 1.2 gives the rigid specifications for this type of interaction. An example is an online purchasing site in which users add items to a cart before the payment is made. Let's assume we have a web service that does the final payment. There can be a firm agreement that the web service will only accept the cart item name, unit price, and quantity. If such a scenario exists then, it's always better to use the SOAP protocol.

Stateful operations – if the application has a requirement that state needs to be maintained from one request to another, then the SOAP 1.2 standard provides the WS* structure to support such requirements.

SOAP vs. REST API challenges

Challenges with the SOAP API

WSDL file - One of the key challenges of the SOAP API is the WSDL document itself. The WSDL document is what tells the client of all the operations that can be performed by the web service. The WSDL document will contain all information such as the data types being used in the SOAP messages and what all operations are available via the web service. The biggest challenge of the WSDL file which is the tight contract between the client and the server and that one change could cause a large impact, on the whole, client applications.

Document size – The other key challenge is the size of the SOAP messages which get transferred from the client to the server. Because of the large messages, using SOAP in places where bandwidth is a constraint can be a big issue.

Challenges with the REST API

Lack of Security – REST does not impose any sort of security like SOAP. This is why REST is very appropriate for public available URL's, but when it comes down to confidential data being passed between the client and the server, REST is the worst mechanism to be used for web services.

Lack of state – Most web applications require a stateful mechanism. For example, if you had a purchasing site which had the mechanism of having a shopping cart, it is required to know the number of items in the shopping cart before the actual purchase is made. Unfortunately, the burden of maintaining this state lies with the client, which just makes the client application heavier and difficult to maintain.