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

@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?

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"; 
    }

}