Over the course of software development, REST APIs are now considered one of the most crucial methods of communication across different systems. REST or Representational State Transfer is a style of software architecture that allows systems to communicate with each other via standard web methods. Since Java is one of the most common programming languages utilized globally, it has been instrumental in constructing REST APIs. Using Java, which has much flexibility and stability, one can create a great deal of secure and scalable RESTful web services.

In this article, we are going to study the process of creating a REST API in Java in more detail, discussing all the involved major aspects, such as: what are the components, what are the steps of the process and what practices are necessary for developers to create a safe and easy-to-work-with API.

What is a REST API?



To put it simply, a REST API is a system that helps applications to exchange data with one another by the means of the REST methodology. Unlike classical web services of the type commonly referred to as SOAP, the REST does not depend on a strict set of standards and is more straightforward in using HTTP protocols which in return makes it easier to develop, test or update.

Through the use of REST APIs, applications are able to interact with resources usually in the form of URLs (Uniform Resource Locators). These resources include a user's profile, a product catalogue, and even records in a database. Triggered by the client, the interaction leverages the HTTP methods of GET, POST, PUT, and DELETE and in turn the server returns data in a structured format, most commonly JSON or XML.

The key characteristics of REST APIs include:

  • Statelessness: Clients are required to specify all relevant information in each request to the server for it to be actionable. The server does not save any session state between requests to allow for sessions to be independent of one another.


  • Client-Server Architecture: A clear separation exists between the client and the server. The client manages the user interface part while the server concentrates on the processing and storage of data.


  • Cacheability: It is possible to have a server response that is marked as either cacheable or non-cacheable making it possible for responses to be stored and reused by clients in order to enhance performance.


  • Layered System: It is also possible to have an ensemble of a load balancer, security layer, caching layer and other components for a single REST API, hence enhancing ability and performance.


Why REST APIs Development Should Be Done in Java?



There are many advantages to developing REST APIs in Java. It is a cross-platform language – Java applications can run on any OS with the JVM installed. This ability to work across multiple platforms is extremely beneficial in developing APIs that will be used from different platforms and devices.

Moreover, Java has an extensive collection of libraries, frameworks, and tools that simplify the process of API development. It also greatly enhances security, error processing, data handling, and vertical scaling, which is why Java is used to develop enterprise grade web services.

The multi-threaded nature of Java allows it to serve a very high number of concurrent requests, making it ideal for developing APIs that will be subjected to heavy traffic. The large developer community in Java makes resources available while adding credibility and security for web applications and services.

Fundamentals of Developing RESTful APIs Using Java



Now before jumping to the nitty gritty of how a REST API is created using Java, there are some fundamental aspects that you need to grasp that will be handy during the development process. Apart from assisting you in the creation of functioning REST APIs, these principles will help streamline the design structure of your API discouraging bad practices that may affect maintenance.

REST API Resources



A term that is quite often used in REST API development are resources. These are basically what the API manages. For instance, a REST API that handles a book shop might have books, authors and categories as resources. Each resource is served with a unique URI (Uniform Resource Identifier) that enables clients to perform actions on it.


For instance, for a collection of books, the URI would be /books and for a specific book using its unique identifier it would be /books/{id} .

With the help of standard HTTP commands, clients are able to access and perform actions on resources. Every resource has a unique URI. In this instance the four CRUD (Create, Read, Update, Delete) actions that correspond with the four common commands are:

  • GET: This commands the servers to send back data that it has.


  • POST: This commands to create new data on the server.


  • PUT: Is used to modify an existing document or resource present in the server.


  • DELETE: Eliminates an item/document from the server.


Getting to Understand CRUD Operations in REST APIs



To the client and server portions of the architecture, the commonest data format in information transportation, especially in representations of web APIs (Application Programming Interface), is the JSON (JavaScript Object Notation) structure. This format has a weak structure and can easily be read by anyone as it is simple, easy and quick to format and suitable for web data transmission.

In Java, you can use libraries like Gson or Jackson to convert Java objects into JSON and vice versa. In most cases, JSON is the format that APIs built with Java tend to respond to and the clients also tend to request the data in that format.

Dependency on Previous Requests



One of the basic requirements for REST architecture is statelessness where it is said that every new HTTP request raised by the client is self-sufficient and does not require input from the server regarding any of the client’s previous requests. This implies that a server on a REST architecture is not aware of any other requests made by the client.

The lack of states streamlines the construction of the API and guarantees that the server does not have to control the state of users, or other states between calls. On the contrary, it also means that all states that are needed must be included in the request such as the body of the request, tokens for authentication, input parameters for queries and so on.

HTTP Status Codes



In the case of developing a REST API in Java, one of the amusements in the process is to include HTTP status codes in your responses. These codes are crucial for clients since they inform them whether or not their request was executed properly. The following are some of the commonly used status codes:

  • 200 OK: Successful request with the response body containing data to satisfy the request.


  • 201 Created: Successful request with the newly created resource in the response body.


  • 400 Bad Request: The request could not be processed due to malformed syntax or a violation of the server's API.


  • 404 Not Found: Serves as a response when the asked resource is not able to be fetched by the client.


  • 500 Internal Server Error: This indicates that an unexpected error happened on the website’s server.


By ensuring that the correct status codes are provided, you assist clients in coping up with the responses and errors generated by the web server.

Authentication and Security



Since REST API employs mechanisms whereby sensitive information and data are exchanged, it is important to protect your API. Java provides several means of authenticating and thus authorising API requests which include the following:

  • Basic Authentication: This is a straightforward way of authentication whereby a client requests with a username and password on every request the client sends.


  • Oauth: Is a more modern authentication technique that enables third party apps to get user information without the need to give them their logins.


  • JWT (JSON Web Tokens): The secured way for exchange of information through compact and URL-safe token format specification between the client and server.