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Request Parameters

Basic Spring
≈ 2 min read

Data from the URL as method arguments

Some input data arrives not in the request body, but directly in the URL. Spring MVC can pass such values straight into Java method parameters, so the controller does not need to parse the request string manually.

Query parameters with @RequestParam

For the request GET /products?category=books&page=2, the values after ? can be obtained conveniently with @RequestParam. 

@GetMapping("/products")
List<ProductDto> products(
        @RequestParam String category,
        @RequestParam(defaultValue = "0") int page) {
    return productService.find(category, page);
}

Spring MVC takes string values from the HTTP request and converts them into the declared Java types when such conversion is supported. In the example, page becomes an int, and when the parameter is missing the value 0 is used.

Path variables with @PathVariable

If a value is part of the path itself, it is marked with braces in the mapping and obtained with @PathVariable. 

@GetMapping("/products/{id}")
ProductDto product(@PathVariable long id) {
    return productService.find(id);
}

The GET /products/42 request passes the value 42 into id. The URL stays part of the external contract, while inside the controller we already work with a regular Java value.

A query parameter and a path variable express different things. A path variable is usually used to identify a resource, while query parameters are used for filtering, sorting, pagination, and other additional request conditions.
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