基础使用
ModelMapper
ModelMapper 是轻量级的帮助我们在不同的 Java POJO 之间进行转换的工具库，其引入方式如下：
<dependency>
<groupId>org.modelmapper</groupId>
<artifactId>modelmapper</artifactId>
<version>2.3.0</version>
</dependency>
基础使用
Mapping
// Source Model
// Assume getters and setters on each class
class Order {
Customer customer;
Address billingAddress;
}
class Customer {
Name name;
}
class Name {
String firstName;
String lastName;
}
class Address {
String street;
String city;
}
// Destination Model
// Assume getters and setters
class OrderDTO {
String customerFirstName;
String customerLastName;
String billingStreet;
String billingCity;
}
然后可以使用 ModelMapper 来将 order 实例映射到 OrderDTO：
ModelMapper modelMapper = new ModelMapper();
OrderDTO orderDTO = modelMapper.map(order, OrderDTO.class);
assertEquals(order.getCustomer().getName().getFirstName(), orderDTO.getCustomerFirstName());
assertEquals(order.getCustomer().getName().getLastName(), orderDTO.getCustomerLastName());
assertEquals(order.getBillingAddress().getStreet(), orderDTO.getBillingStreet());
assertEquals(order.getBillingAddress().getCity(), orderDTO.getBillingCity());
Explicit Mapping
很多时候我们也可以手动地指明映射规则：
modelMapper.addMappings(mapper -> {
mapper.map(src -> src.getBillingAddress().getStreet(),
Destination::setBillingStreet);
mapper.map(src -> src.getBillingAddress().getCity(),
Destination::setBillingCity);
});
Spring 中 Entity 与 DTO 的转化
DTO 层
以 Post 为例，我们的 DTO 定义如下：
public class PostDto {
private static final SimpleDateFormat dateFormat = new SimpleDateFormat(
"yyyy-MM-dd HH:mm"
);
private Long id;
private String title;
private String url;
private String date;
private UserDto user;
public Date getSubmissionDateConverted(String timezone)
throws ParseException {
dateFormat.setTimeZone(TimeZone.getTimeZone(timezone));
return dateFormat.parse(this.date);
}
public void setSubmissionDate(Date date, String timezone) {
dateFormat.setTimeZone(TimeZone.getTimeZone(timezone));
this.date = dateFormat.format(date);
}
// standard getters and setters
}
这里值得注意的是对于两个日期相关的处理方法：
- getSubmissionDateConverted() 方法根据传入的 timezone 将当前时间转化为服务端内置的 Post 实例所需要的时区。
- setSubmissionDate 则是将 Post 时区转化为用户当前的时区，以返回给用户。
Service 层
服务层的操作如下：
public List<Post> getPostsList(
int page, int size, String sortDir, String sort) {
PageRequest pageReq
= PageRequest.of(page, size, Sort.Direction.fromString(sortDir), sort);
Page<Post> posts = postRepository
.findByUser(userService.getCurrentUser(), pageReq);
return posts.getContent();
}
Controller 层
Controller 中会调用对应的 Service 中的方法来获取数据，并且将其转化为用户侧的 DTO 数据：
@Controller
class PostRestController {
@Autowired
private IPostService postService;
@Autowired
private IUserService userService;
@Autowired
private ModelMapper modelMapper;
@GetMapping
@ResponseBody
public List<PostDto> getPosts(...) {
//...
List<Post> posts = postService.getPostsList(page, size, sortDir, sort);
return posts.stream()
.map(this::convertToDto)
.collect(Collectors.toList());
}
@PostMapping
@ResponseStatus(HttpStatus.CREATED)
@ResponseBody
public PostDto createPost(@RequestBody PostDto postDto) {
Post post = convertToEntity(postDto);
Post postCreated = postService.createPost(post));
return convertToDto(postCreated);
}
@GetMapping(value = "/{id}")
@ResponseBody
public PostDto getPost(@PathVariable("id") Long id) {
return convertToDto(postService.getPostById(id));
}
@PutMapping(value = "/{id}")
@ResponseStatus(HttpStatus.OK)
public void updatePost(@RequestBody PostDto postDto) {
Post post = convertToEntity(postDto);
postService.updatePost(post);
}
}
我们实际的转化函数定义如下：
private PostDto convertToDto(Post post) {
PostDto postDto = modelMapper.map(post, PostDto.class);
postDto.setSubmissionDate(post.getSubmissionDate(),
userService.getCurrentUser().getPreference().getTimezone());
return postDto;
}
private Post convertToEntity(PostDto postDto) throws ParseException {
Post post = modelMapper.map(postDto, Post.class);
post.setSubmissionDate(postDto.getSubmissionDateConverted(
userService.getCurrentUser().getPreference().getTimezone()));
if (postDto.getId() != null) {
Post oldPost = postService.getPostById(postDto.getId());
post.setRedditID(oldPost.getRedditID());
post.setSent(oldPost.isSent());
}
return post;
}