@RequestBody how to differentiate an unsent value from a null value?

Question

@PatchMapping("/update")
HttpEntity<String> updateOnlyIfFieldIsPresent(@RequestBody Person person) {
    if(person.name!=null) //here
}

how to differentiate an unsent value from a null value? How can I detect if client sent null or skipped field?

Answer 1

The above solutions would require some change in the method signature to overcome the automatic conversion of request body to POJO (i.e. Person object).

Method 1:-

Instead of converting the request body to POJO class (Person), you can receive the object as Map and check for the existence of the key "name".

@PatchMapping("/update")
public String updateOnlyIfFieldIsPresent1(@RequestBody Map<String, Object> requestBody) {

    if (requestBody.get("name") != null) {
        return "Success" + requestBody.get("name"); 
    } else {
        return "Success" + "name attribute not present in request body";    
    }


}

Method 2:-

Receive the request body as String and check for the character sequence (i.e. name).

@PatchMapping("/update")
public String updateOnlyIfFieldIsPresent(@RequestBody String requestString) throws JsonParseException, JsonMappingException, IOException {

    if (requestString.contains("\"name\"")) {
        ObjectMapper mapper = new ObjectMapper();
        Person person = mapper.readValue(requestString, Person.class);
        return "Success -" + person.getName();
    } else {
        return "Success - " + "name attribute not present in request body"; 
    }

}