How to inject single json parameter value in @PostMapping

Question

I have a simple POST servlet and want to inject only one single property of a JSON request:

@RestController
public class TestServlet {
    @PostMapping(value = "/test", consumes = APPLICATION_JSON_VALUE)
    public String test(@Valid @NotBlank @RequestBody String test) {
        return test;
    }
}

Request:

{
    "test": "random value",
    "some": "more"
}

Result: the test parameter contains the whole json, not the parameter value only. Why? How can I achieve this without having to introduce an extra Bean?

Answer 1

You can't expect Spring to guess that you want to parse the json to extract the "test" field.

If you don't want an extra bean, use a Map<String, String> and get the value with "test" key :

@RestController
public class TestServlet {
    @PostMapping(value = "/test", consumes = APPLICATION_JSON_VALUE)
    public String test(@Valid @NotBlank @RequestBody Map<String, String> body) {
        return body.get("test");
    }
}