Rest-assured. Is it possible to extract value from request json?

You can also do like this if you’re only interested in extracting the “user_id”:

String userId = 
given().
        contentType("application/json").
        body(requestBody).
when().
        post("/admin").
then().
        statusCode(200).
extract().
        path("user_id");

In its simplest form it looks like this:

String userId = get("/person").path("person.userId");