patchable

The Optional type for PATCH requests.

A Patchable is a opinionated class that mimics the Java 8 Optional with an extra field - isSet. That way we can know in a PATCH request if the client is actually sending a null or the value should simply be omitted.

Example

Given the following request bean:

public class UserPatch {
    private Patchable<String> name = Patchtable.notSet();
    private Patchable<Integer> age = Patchtable.notSet();
    
    public Patchable<String> getName() {
        return this.name;
    }
    
    public Patchable<Integer> getAge() {
        return this.age;
    }
}

we can check with isSet if the value was present in the JSON:

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new PatchableModule());
UserPatch userPatch = objectMapper.readValue("{\"name\": \"Juan\"}", UserPatch.class);

userPatch.getName().isSet(); // true
userPatch.getAge().isSet();  // false

Furthermore, we can use the ifSet utility method:

// Read entity from database
User userEntity = repository.getUser();

// Apply changes only to the actually set fields from the PATCH request
userPatch.getName().ifSet(userEntity::setName)
userPatch.getAge().ifSet(userEntity::setAge)

Features & Behavior

Patchable currently has Jackson support. To enable the serialization / deserialization behavior the PatchableModule() must be registered to the Jackson ObjectMapper.

ObjectMapper appMapepr = new ObjectMapper();
mapper.registerModule(new PatchableModule());

Serialization

When serializing to JSON, the Patchable's value is added to the result JSON only if it actually has a set value.

UserPatch patch = new UserPatch();
// patch.setName("..."); commented out
patch.setAge(10);

appMapper.writeValueAsString(patch); // {"age": 10}

Deserialization

The bean we deserialize into should initialize all Patchable<T> fields as Patchable.notSet(). The value will be overriden by the deserializer only if the field value is present in the JSON.

Validation

Supports Hibernate Validator. Validation only triggers if the Patchable has a set value. Example:

public class UserPatch {

    private Patchable<@NotNull @Email String> email = Patchable.of("not_email");
}