Master Spring RestController: The Definitive Guide with Examples

Want to build powerful, flexible RESTful APIs in Spring? This article provides a concise, practical guide to using Spring RestController, packed with code examples and clear explanations. Learn how to handle JSON and XML, customize request and response formats, and build robust web services.

What is Spring RestController? (And Why Should You Use It?)

Spring RestController is a specialized controller in the Spring framework for creating RESTful web services. Think of it as a streamlined way to build APIs that respond with data, not just HTML pages.

• It combines @Controller and @ResponseBody, simplifying your code.
• Automatically converts your Java objects to JSON or XML.
• Makes building APIs faster and easier.

Project Setup: Dependencies for Your Spring RestController

To get started, you'll need a few key dependencies in your pom.xml (Maven) file. These libraries enable Spring MVC, JSON processing, and XML handling:

• spring-webmvc: For Spring MVC framework.
• jackson-databind: For converting Java objects to/from JSON.
• jaxb-api & jaxb-runtime: For handling XML requests and responses.

Configure Spring MVC for JSON & XML

To handle both JSON and XML, you need to configure Spring MVC. This involves defining message converters.

• Define jsonMessageConverter and xmlMessageConverter beans.
• Set them in the RequestMappingHandlerAdapter's messageConverters property.
• This tells Spring which beans to use for transforming data.

Spring RestController: Code Example Breakdown

Here's a simple Spring RestController example to illustrate the key concepts:

@RestController
public class EmployeeRestController {

 @Autowired
 private EmployeeRepository repository;

 @GetMapping("/rest/employee/get/{id}")
 public Employee getEmployeeByID(@PathVariable("id") int id) {
 return repository.retrieve(id);
 }

 @PostMapping("/rest/employee/create")
 public Employee createEmployee(@RequestBody Employee emp) {
 repository.store(emp);
 return emp;
 }
}

• @RestController: Marks the class as a REST controller.
• @GetMapping: Maps HTTP GET requests to specific handler methods.
• @PostMapping: Handles HTTP POST requests, often for creating resources.
• @PathVariable: Extracts values from the URL path (e.g., the employee ID).
• @RequestBody: Binds the request body to a method parameter (e.g., an Employee object).

Content Negotiation: JSON vs. XML

Spring uses the Accept and Content-Type headers to determine the format.

• Content-Type tells the server the format of the data you're sending (e.g., application/json or application/xml).
• Accept indicates the format the client wants in the response.

Testing Your Spring RestController: Practical Examples

Use tools like Postman to test your APIs. Set the Accept header to application/json to receive a JSON response, or application/xml for XML.

For GET requests, the Accept header is key. For POST requests, you'll also need to set the Content-Type header to match the format of the request body.

Real-World Example:

Imagine you're building an e-commerce API. A GET request to /products/123 with Accept: application/json would return product details in JSON format. A POST request to /orders with Content-Type: application/json would create a new order from the JSON data you provide.

Maximize the Power of Spring RestController

Spring RestController simplifies REST API development by handling data conversion and request mapping. Using Content Negotiation, jaxb-api and jackson-databind, you can support any Accept and Content-Type request headers your needs require.