java - 模型映射器 - 如何映射不兼容的类型

Question

我有实体 User和Event其中有many to many彼此的关系。如果我尝试将 User 对象从 Controller 返回到 REST API，则会导致循环依赖。

我决定使用DTOs我会用 List<Event> 代替只是List<Integer>这将代表事件对象的 ID。

但是如果我尝试创建自定义 PropertyMap ， 这是行不通的。您是否推荐不同的方法，如何做？

事件实体

@Entity
@Table(name = "events")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Event extends AbstractEntity {

@ManyToMany(cascade = CascadeType.PERSIST)
@JoinTable(name = "event_participants",
        joinColumns = @JoinColumn(name = "event_id"),
        inverseJoinColumns = @JoinColumn(name = "user_id"))
private List<User> eventParticipants;

用户实体

@Entity
@Table(name = "users")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class User extends AbstractEntity {

@ManyToMany(mappedBy = "eventParticipants")
private List<Event> participatingEvents;

用户 Controller

@RestController
@RequestMapping("/users")
public class UserController extends AbstractController {

@Autowired
private UserService userService;

@Autowired
private ModelMapper modelMapper;

@RequestMapping(method = RequestMethod.GET, value = "/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
public UserDTO find(@PathVariable("id") Integer id) {
    final User user = userService.find(id);
    if (user == null) {
        //TODO throw some exception
        return null;
    }
    UserDTO userDTO = userToDTO(user);
    return userDTO;
}

private UserDTO userToDTO(User user) {
    modelMapper.addMappings(new UserMap());
    return modelMapper.map(user, UserDTO.class);
}

最后，我的PropertyMap类

public class UserMap extends PropertyMap<User, UserDTO> {

    @Override
    protected void configure() {
        map().setFirstName(source.getFirstName());

        map().setLastName(source.getLastName());

        map().setEmail(source.getEmail());

        List<Integer> friendsDTO = new ArrayList<>();
        for(User u : source.getFriends()){
            friendsDTO.add(u.getId());
        }
        map().setFriends(friendsDTO);

        List<Integer> participatingEventsDTO = new ArrayList<>();
        for(Event e : source.getParticipatingEvents()){
            participatingEventsDTO.add(e.getId());
        }
        map().setParticipatingEvents(participatingEventsDTO);

        List<Integer> ownedEventsDTO = new ArrayList<>();
        for(Event e : source.getOwnedEvents()){
            ownedEventsDTO.add(e.getId());
        }
        map().setOwnedEvents(ownedEventsDTO);

        List<Integer> commentsDTO = new ArrayList<>();
        for(Comment c : source.getComments()){
            commentsDTO.add(c.getId());
        }
        map().setComments(commentsDTO);

        List<Integer> thingsDTO = new ArrayList<>();
        for(ThingToTake t : source.getThingsToTakeList()){
            thingsDTO.add(t.getId());
        }
        map().setThingsToTakeList(thingsDTO);
    }

}

如果我尝试使用休息来获取，这是一个异常:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.modelmapper.ConfigurationException: ModelMapper configuration errors:

1) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

2) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

3) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

4) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

5) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

5 errors
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

org.modelmapper.ConfigurationException: ModelMapper configuration errors:

1) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

2) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

3) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

4) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

5) Invalid source method java.util.List.add(). Ensure that method has zero parameters and does not return void.

5 errors
    org.modelmapper.internal.Errors.throwConfigurationExceptionIfErrorsExist(Errors.java:241)
    org.modelmapper.internal.ExplicitMappingBuilder.visitPropertyMap(ExplicitMappingBuilder.java:229)
    org.modelmapper.PropertyMap.configure(PropertyMap.java:380)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:483)
    org.modelmapper.internal.ExplicitMappingBuilder.build(ExplicitMappingBuilder.java:195)
    org.modelmapper.internal.TypeMapImpl.addMappings(TypeMapImpl.java:72)
    org.modelmapper.internal.TypeMapStore.getOrCreate(TypeMapStore.java:101)
    org.modelmapper.ModelMapper.addMappings(ModelMapper.java:93)
    com.ear.tripplan.rest.UserController.userToDTO(UserController.java:50)
    com.ear.tripplan.rest.UserController.find(UserController.java:39)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:483)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

Answer 1

我也遇到了同样的问题我通过将 id 包装在另一个对象中来做到这一点

public class UserDTO {

     List<EventDTO> participatingEvents
     /// getter setter
}

public class EventDTO {
    private Long id;
    // getter setter
}

并且您不需要任何 propertyMap 或转换器

UserDTO userDTO = modelmapper.map(user, UserDTO.class);

希望对你有帮助

已更新

您也可以使用转换器来做到这一点

public class UserMap extends PropertyMap<User, UserDTO> {

@Override
protected void configure() {
    Converter<List<User>, List<Long>> converter = new AbstractConverter<List<User>, List<Long>>() {
        List<Long> result = new ArrayList<>();
        @Override
        protected List<Long> convert(List<User> source) {
            source.forEach(user -> result.add(user.getId()));
            return result;
        }
    };
    using(converter).map(source.getUsers(), destination.getUsers());
}

}