How to map Page to Page in spring-data-rest

问题

When I hit the database with PagingAndSortingRepository.findAll(Pageable) I get Page<ObjectEntity>. However, I want to expose DTO's to the client and not entities. I can create DTO just by injecting entity into it's constructor, but how do I map the entities in Page object to DTO's? According to spring documentation, Page provides read-only operations.

Also, Page.map is not possibility, as we don't have support for java 8. How to create the new Page with mapped objects manually?

回答1:

You can still use the Page.map without lambda expressions:

Page<ObjectEntity> entities = objectEntityRepository.findAll(pageable);
Page<ObjectDto> dtoPage = entities.map(new Converter<ObjectEntity, ObjectDto>() {
    @Override
    public ObjectDto convert(ObjectEntity entity) {
        ObjectDto dto = new ObjectDto();
        // Conversion logic

        return dto;
    }
});

回答2:

In Spring Data 2, the Page map method takes a Function instead of a Converter, but it still works basically the same as @Ali Dehghani described.

Using Function:

Page<ObjectEntity> entities = objectEntityRepository.findAll(pageable);
Page<ObjectDto> dtoPage = entities.map(new Function<ObjectEntity, ObjectDto>() {
    @Override
    public ObjectDto apply(ObjectEntity entity) {
        ObjectDto dto = new ObjectDto();
        // Conversion logic

        return dto;
    }
});

回答3:

Here is my solution, thanks to @Ali Dehghani

private Page<ObjectDTO> mapEntityPageIntoDTOPage(Page<ObjectEntity> objectEntityPage) {
        return objectEntityPage.map(new Converter<ObjectEntity, ObjectDTO>() {
            public ObjectDTO convert(ObjectEntity objectEntity) {
                return new ObjectDTO(objectEntity, httpSession);
            }

        });
    }

回答4:

And in java8:

Page<ObjectEntity> entities = 
 objectEntityRepository.findAll(pageable)
 .map(ObjectDto::fromEntity);

Where fromEntity is a static method on ObjectDto that contains the conversion logic.

回答5:

You can use Page.map by simply doing this:

public Page<ObjectDto> toPageObjectDto(Page<Object> objects) {
    Page<ObjectDto> dtos  = objects.map(this::convertToObjectDto);
    return dtos;
}

private ObjectDto convertToObjectDto(Object o) {
    ObjectDto dto = new ObjectDto();
    //conversion here
    return dto;
}

回答6:

At the end, you will not return the Page to the users, but a list of ObjectDTO, with the Page details at the header, so this would be my solution.

ObjectService

public Page<ObjectEntity> findAll (Pageable pageable){
  //logic goes here.
  Page<ObjectEntity> page = objectRepository.findAll(pageable);
  return page;
}

ObjectResource / rest (the exposed endpoint)

@GetMapping
public ResponseEntity<List<ObjectDTO>> findAll (Pageable pageable){
  Page<ObjectEntity> page = objectServiceService.findAll(pageable);

  HttpHeaders headers = PaginationUtil.generatePaginationHttpHeaders(page, "your-endpoint-here");

  return new ResponseEntity<>(objectMapper.toDto(page.getContent()), headers, HttpStatus.OK);
}

The reason for using this is so that you don't need to duplicate the page details for ObjectEntity and DTO. It is key to note that a page contains the following: