Representational State Transfer (REST) is designed to take advantage of the existing protocols. The consistent systems of REST are often called RESTful systems. It can be used over almost every protocol, but it normally takes advantage of HTTP during the use of web APIs. It makes it simpler for systems to speak with one another. These systems are portrayed by how they are stateless and separate the concerns of the client and server. We will go in depth into what these terms mean and why they are advantageous qualities for services on the web.

A RESTful web service is responded to with a payload formatted in either HTML, XML, JSON, or some other format. The response can affirm that a change has been made to the requested response, and the reaction can give hypertext links that are related to other resources, or a bundle of resources. At the point in which HTTP is utilized, as is normal, the tasks that are accessible are GET, POST, PUT, DELETE, and other predefined HTTP functions.

To use Spring for Android, you can use different HTTP libraries. Spring has suggested using RestTemplate for Android. This is now outdated and may not be supported for the newer Android version. However, now, you can find some libraries that are easier and more powerful, with lots of features. You can use a different HTTP library, such as  one of the following:

• RestTemplate
• Retrofit
• Volley

We will explore the use of all of these libraries in this chapter. In our upcoming chapters, we will use Retrofit because it's easier, updated, robust, and requires less code to be written. However, you can use any of them in your projects.