检查 Spring 引导 RestAPI 的字段的最佳方法是什么

Question

What is the best way to find out which user fields are provided? eg the following payload should update the name of the user, and convert age to null but it should not modify the address-field.

curl -i -X PATCH http://localhost:8080/123 -H "Content-Type: application/json-patch+json" -d '{
    "name":"replace",
    "age":null
}'

@PatchMapping(path = "/{id}", consumes = "application/json-patch+json")
public ResponseEntity<User> updateUser(@PathVariable String id, @RequestBody User user) {
  ... handle user based on which fields are provided
}

@Data
@JsonIgnoreProperties(ignoreUnknown = true)
public class User { 
  private String name;
  private Integer age;
  private String address;
  ...
}

Using @JsonIgnoreProperties-annotation allows various payloads but it converts missing values to nulls. Therefore, there is no way to check is the actual field provided or is the field's value just null. How should I check difference of those two cases?

Answer 1

It is possible to add boolean flags which should be set to true in the setters and then to check these flags when updating the values in the DB, but this will resurrect a lot of bolerplate code:

@Data
public class User { 
  private String name;
  private Integer age;
  private String address;
  
  @JsonIgnore
  private boolean nameSet = false;

  @JsonIgnore
  private boolean ageSet = false;

  @JsonIgnore
  private boolean addressSet = false;

  public void setName(String name) {
      this.name = name;
      this.nameSet = true;
  }
  // ... etc.
}

public ResponseEntity<User> updateUser(@PathVariable String id, @RequestBody User user) {
  //... handle user based on which fields are provided
    User db = userRepo.byId(id);

    boolean changed = user.isNameSet() || user.isAgeSet() || user.isAddressSet();

    if (changed) {
        if (user.isNameSet()) db.setName(user.getName());
        // etc.

        userRepo.save(db);
    }
}