Spring HATEOAS 和实体 DTO - ModelAssembler 的问题

Question

我正在开发 Spring HATEOAS REST api。 现在我遇到了隐藏Employee类的一些字段（我想隐藏其中一些）。 据我了解，必须使用 DTO（数据传输对象）。所以我创建了只包含我需要的这个字段的新类（EmployeeDTO）。我正在使用ModelMapper 映射适当的字段。

所以现在，我遇到了数据类型的问题。我是否必须将控制器中的所有返回值从 Employee 更改为 EmployeeDTO？然后更改 ModelAssembler 中的所有内容？

或者也许 DTO 类应该extends RepresentationModel？ （这也迫使它在实体中扩展）。 期待您的帮助，所有这些看起来有点混乱（更改所有返回类型），我觉得应该有更聪明的解决方案。

我现在就是这样：

EmployeeController 中的方法：

@GetMapping(value = "/{id}", produces = "application/hal+json")
    public EntityModel<Employee> getEmployeeById(@PathVariable Long id) {
        Optional<Employee> employee = employeeService.findById(id);
        return employeeModelAssembler.toModel(employee.get());
}

@GetMapping(value = "", produces = "application/hal+json")
    public CollectionModel<EntityModel<Employee>> getAllEmployees() {
        List<Employee> employeesList = EmployeeService.findall();
        return employeeModelAssembler.toCollectionModel(EmployeesList);
}

EmployeeModelAssembler（在控制器中自动装配）：

public class EmployeeModelAssembler implements RepresentationModelAssembler<Employee, EntityModel<Employee>> {

    @Override
    public EntityModel<Employee> toModel(Employee employee) {
        EntityModel<Employee> employeeEntityModel = EntityModel.of(employee);

        Link selfLink = linkTo(methodOn(EmployeeController.class).getEmployeeById(employee.getId())).withSelfRel();
        employeeEntityModel.add(selfLink);

        return employeeEntityModel;
    }

    @Override
    public CollectionModel<EntityModel<Employee>> toCollectionModel(Iterable<? extends Employee> entities) {

        List<Employee> employeesList = (List<Employee>) entities;
        List<EntityModel<Employee>> employeeEML = employeesList.stream().map(this::toModel).collect(Collectors.toList());

        Link selfLink = linkTo(methodOn(EmployeeController.class).getAllEmployees()).withSelfRel();

        return CollectionModel.of(employeeEML, selfLink);
    }
}

编辑

这是我在另一个控制器中访问这个 hal+json 响应的方式。目标是获取 EmployeeDTO 对象列表：

String uri = "http://localhost:8080/api/employees";

Traverson traverson = new Traverson(URI.create(uri), MediaTypes.HAL_JSON);
Traverson.TraversalBuilder tb = traverson.follow("href");

ParameterizedTypeReference<CollectionModel<EmployeeDTO>> typeReference = new ParameterizedTypeReference<CollectionModel<EmployeeDTO>>() {};
CollectionModel<EmployeeDTO> resEmployees = tb.toObject(typeReference);
Collection<EmployeeDTO> employees = resEmployees.getContent();

ArrayList<EmployeesDTO> employeesList = new ArrayList<>(employees);

for(EmployeesDTO x : employeesList) {
    System.out.println(x);
    System.out.println(x.getLinks());
}

Answer 1

如果您想将 API 公开的资源与 JPA 实体分离，这是一个好主意，您必须更新控制器以处理适当的类型。

请看下面的例子：

首先，假设您有以下 DTO：

public class EmployeeDTO extends RepresentationModel<EmployeeDTO> {
      private long id;
      private String surname;
      private String departmentId;

      // getters and setters
}

请注意我没有将您的 JPA 实体（员工）与 DTO 混合。

现在应该更新您的控制器以返回适当的类型。

@GetMapping(value = "/{id}", produces = "application/hal+json")
public EmployeeDTO getEmployeeById(@PathVariable long id) {
       Optional<Employee> employee = employeeService.findById(id);
       return employeeModelAssembler.toModel(employee.get());
}

@GetMapping(value = "", produces = "application/hal+json")
public CollectionModel<EmployeeDTO> getAllEmployees() {
    List<Employee> employeesList = employeeService.findAll();
    return employeeModelAssembler.toCollectionModel(employeesList);
}

还有一个 ModelAssembler 的例子

@Component
public class EmployeeModelAssembler implements RepresentationModelAssembler<Employee, EmployeeDTO> {

    @Override
    public EmployeeDTO toModel(Employee employee) {
        ModelMapper modelMapper = new ModelMapper();
        EmployeeDTO employeeDto = modelMapper.map(employee, EmployeeDTO.class);

        Link selfLink = linkTo(methodOn(EmployeeController.class).getEmployeeById(employee.getId())).withSelfRel();
        employeeDto.add(selfLink);

        return employeeDto;
    }

    @Override
    public CollectionModel<EmployeeDTO> toCollectionModel(Iterable<? extends Employee> employeesList) {
       ModelMapper modelMapper = new ModelMapper();
       List<EmployeeDTO> employeeDTOS = new ArrayList<>();

       for (Employee employee : employeesList){
           EmployeeDTO employeeDto = modelMapper.map(employee, EmployeeDTO.class);
           employeeDto.add(linkTo(methodOn(EmployeeController.class)
                                .getEmployeeById(employeeDto.getId())).withSelfRel());
           employeeDTOS.add(employeeDto);
        }

        return new CollectionModel<>(employeeDTOS);
    }
}

假设我有一个员工端点，我对其进行了测试并得到了以下响应

获得员工/1

{
"id": 1,
"surname": "teste",
"departmentId": "1",
"_links": {
    "self": {
        "href": "http://localhost:8080/employees/1"
    }
}
}

找员工

{
    "_embedded": {
        "employeeDtoList": [
            {
                "id": 1,
                "surname": "teste",
                "departmentId": "1",
                "_links": {
                    "self": {
                        "href": "http://localhost:8080/employees/1"
                    }
                }
            },
            {
                "id": 2,
                "surname": "teste",
                "departmentId": "2",
                "_links": {
                    "self": {
                        "href": "http://localhost:8080/employees/2"
                    }
                }
            }
        ]
    }
}