Mapstruct for PATCH operations

pom.xml

<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct</artifactId>
    <version>${mapstruct.version}</version>
</dependency>

TaskController.java

import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.Schema;
import io.swagger.v3.oas.annotations.responses.ApiResponse;
import io.swagger.v3.oas.annotations.responses.ApiResponses;
import io.swagger.v3.oas.annotations.tags.Tag;
import lombok.RequiredArgsConstructor;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.web.bind.annotation.*;

import javax.validation.ConstraintViolationException;
import java.util.List;

import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

@RequiredArgsConstructor
@RestController
@RequestMapping(TaskController.BASE_URL)
@Tag(name = "task")
public class TaskController {

	public static final String BASE_URL = "/api/task";

	private final TaskService taskService;
	private final TaskMapper taskMapper;

	// ...
  
	@Operation(summary = "Partial update of a task")
	@ApiResponses({
		@ApiResponse(responseCode = "200", description = "Successful operation"),
		@ApiResponse(responseCode = "404", description = "Task not found",
			content = @Content(schema = @Schema(implementation = ApiError.class)))
	})
	@PatchMapping("/{taskId}")
	public TaskDto patchTask(@PathVariable Long taskId, @RequestBody TaskDto taskDto) {
		Task task = taskMapper.taskDtoToTask(taskDto);
		Task savedTask = taskService.update(taskId, task);
		return taskMapper.taskToTaskDto(savedTask);
	}

	// ...
}

TaskMapper.java

import org.mapstruct.*;

@Mapper
public interface TaskMapper {

	@BeanMapping(nullValuePropertyMappingStrategy = NullValuePropertyMappingStrategy.IGNORE)
	void mergeTasks(Task newTask, @MappingTarget Task oldTask);
}

TaskMapperImpl.java

import javax.annotation.processing.Generated;
import org.springframework.stereotype.Component;

@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    date = "2019-11-26T00:31:50+0100",
    comments = "version: 1.3.1.Final, compiler: javac, environment: Java 11.0.4 (Azul Systems, Inc.)"
)
@Component
public class TaskMapperImpl implements TaskMapper {

    @Override
    public void mergeTasks(Task newTask, Task oldTask) {

        if ( newTask != null ) {
            if ( newTask.getId() != null ) {
                oldTask.setId( newTask.getId() );
            }
            
            // ...
        }
    }
}

TaskServiceImpl.java

import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Service;

import java.util.List;

@RequiredArgsConstructor
@Service
public class TaskServiceImpl implements TaskService {

	private final TaskRepository taskRepository;
	private final TaskMapper taskMapper;

  // ...

	@Override
	public Task update(Long id, Task newTask) {
		Task savedTask = get(id);
		newTask.setId(null);
		taskMapper.mergeTasks(newTask, savedTask);

		return taskRepository.save(savedTask);
	}

	// ...
}