Spring - @PathVariable

A Spring annotation called @PathVariable specifies that a method parameter should be tied to a URI template variable.

@GetMapping("/api/products/{id}")
@ResponseBody
public String getProductsById(@PathVariable String id) {
    return "ID: " + id;
}

A simple GET request to /api/products/{id} will invoke getProductsById with the extracted id value:

http://localhost:8080/api/products/333 
---- 
ID: 333

We may also specify the path variable name:

@GetMapping("/api/products/{id}")
@ResponseBody
public String getProductsById(@PathVariable("id") String productId) {
    return "ID: " + productId;
}

One Class to Rule Them All 🪄

Best practice to handle not required path variables is to combine with Java Optional. In this way, you are both able to handle exceptions and the logic.

@GetMapping(value = { "/api/products", "/api/products/{id}" })
@ResponseBody
public String getProducts(@PathVariable Optional<String> id) {
    if (id.isPresent()) {
        return "ID: " + id.get();
    } else {
        return "ID missing";
    }
}

Now if we don't specify the path variable id in the request, we get the default response:

http://localhost:8080/api/employeeswithoptional 
----
ID missing