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Overview of @RequestParam in Spring Boot

In Spring Boot, the @RequestParam annotation is used to extract query parameters, form parameters, and parts of multi-part requests from the URL. This annotation is part of the Spring Web module and binds HTTP request parameters to controller method arguments.

Usage​

The @RequestParam annotation can be used in a controller method to extract parameters from the query string of the URL.

Example​

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    @GetMapping("/greet")
    public String greet(@RequestParam(name = "name", defaultValue = "World") String name) {
        return "Hello, " + name + "!";
    }
}

In this example:

  • A GET request to /greet?name=John returns "Hello, John!".
  • A GET request to /greet returns "Hello, World!" due to the default value.

Required Parameters​

By default, @RequestParam is required. If the parameter is not present in the request, Spring will throw an exception.

Example​

@GetMapping("/greet")
public String greet(@RequestParam String name) {
    return "Hello, " + name + "!";
}

If the name parameter is missing in the above example, Spring will throw a MissingServletRequestParameterException.

Optional Parameters​

To make a request parameter optional, set the required attribute to false.

Example​

@GetMapping("/greet")
public String greet(@RequestParam(required = false) String name) {
    return "Hello, " + (name != null ? name : "World") + "!";
}

Default Values​

You can provide a default value for a parameter using the defaultValue attribute. If the parameter is not present in the request, the default value will be used.

Example​

@GetMapping("/greet")
public String greet(@RequestParam(name = "name", defaultValue = "World") String name) {
    return "Hello, " + name + "!";
}

Multiple Parameters​

You can use multiple @RequestParam annotations in a single method to bind multiple parameters.

Example​

@GetMapping("/add")
public String add(@RequestParam int a, @RequestParam int b) {
    return "Sum: " + (a + b);
}

A GET request to /add?a=5&b=3 would return "Sum: 8".

List Parameters​

If a request parameter can have multiple values, you can bind it to a List.

Example​

@GetMapping("/numbers")
public String numbers(@RequestParam List<Integer> numbers) {
    return "Numbers: " + numbers;
}

A GET request to /numbers?numbers=1&numbers=2&numbers=3 would return "Numbers: [1, 2, 3]".

Conclusion​

The @RequestParam annotation in Spring Boot is a powerful tool for extracting parameters from HTTP requests. It allows for required and optional parameters, default values, and can handle multiple and list parameters. By understanding and using @RequestParam, you can create more flexible and robust web applications.