问题描述

我正在使用 spring 数据 (mongoDb)，并且我有我的存储库:

I'm using spring data (mongoDb) and I've got my repository:

public interface StoriesRepository extends PagingAndSortingRepository<Story, String> {}

然后我有一个控制器:

@RequestMapping(method = RequestMethod.GET)
public ResponseEntity<Page<StoryResponse>> getStories(Pageable pageable) {
    Page<StoryResponse> stories = storiesRepository.findAll(pageable).map(StoryResponseMapper::toStoryResponse);
    return ResponseEntity.ok(stories);
}

一切正常，但我无法使用 RestTemplate getForEntity 方法使用我的端点:

Everything works fine, but I can't consume my endpoint using RestTemplate getForEntity method:

def entity = restTemplate.getForEntity(getLocalhost("/story"), new TypeReference<Page<StoryResponse>>(){}.class)

我应该提供什么类来成功反序列化我的实体页面?

What class should I provide to successfully deserialize my Page of entities?

推荐答案

new TypeReference<Page<StoryResponse>>() {}

此语句的问题在于 Jackson 无法实例化抽象类型.您应该向 Jackson 提供有关如何使用具体类型实例化 Page 的信息.但它的具体类型 PageImpl 没有默认构造函数或任何 @JsonCreator，因此您也可以不使用以下代码:

The problem with this statement is that Jackson cannot instantiate an abstract type. You should give Jackson the information on how to instantiate Page with a concrete type. But its concrete type, PageImpl, has no default constructor or any @JsonCreators for that matter, so you can not use the following code either:

new TypeReference<PageImpl<StoryResponse>>() {}

由于您无法将所需的信息添加到 Page 类中，因此最好为 Page 接口创建一个自定义实现，该接口具有默认的无参数构造函数，就像在这个 answer 中一样.然后在类型引用中使用该自定义实现，如下所示:

Since you can't add the required information to the Page class, It's better to create a custom implementation for Page interface which has a default no-arg constructor, as in this answer. Then use that custom implementation in type reference, like following:

new TypeReference<CustomPageImpl<StoryResponse>>() {}

这是从链接问题复制的自定义实现:

Here are the custom implementation, copied from linked question:

public class CustomPageImpl<T> extends PageImpl<T> {
    private static final long serialVersionUID = 1L;
    private int number;
    private int size;
    private int totalPages;
    private int numberOfElements;
    private long totalElements;
    private boolean previousPage;
    private boolean firstPage;
    private boolean nextPage;
    private boolean lastPage;
    private List<T> content;
    private Sort sort;

    public CustomPageImpl() {
        super(new ArrayList<>());
    }

    @Override
    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    @Override
    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    @Override
    public int getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }

    @Override
    public int getNumberOfElements() {
        return numberOfElements;
    }

    public void setNumberOfElements(int numberOfElements) {
        this.numberOfElements = numberOfElements;
    }

    @Override
    public long getTotalElements() {
        return totalElements;
    }

    public void setTotalElements(long totalElements) {
        this.totalElements = totalElements;
    }

    public boolean isPreviousPage() {
        return previousPage;
    }

    public void setPreviousPage(boolean previousPage) {
        this.previousPage = previousPage;
    }

    public boolean isFirstPage() {
        return firstPage;
    }

    public void setFirstPage(boolean firstPage) {
        this.firstPage = firstPage;
    }

    public boolean isNextPage() {
        return nextPage;
    }

    public void setNextPage(boolean nextPage) {
        this.nextPage = nextPage;
    }

    public boolean isLastPage() {
        return lastPage;
    }

    public void setLastPage(boolean lastPage) {
        this.lastPage = lastPage;
    }

    @Override
    public List<T> getContent() {
        return content;
    }

    public void setContent(List<T> content) {
        this.content = content;
    }

    @Override
    public Sort getSort() {
        return sort;
    }

    public void setSort(Sort sort) {
        this.sort = sort;
    }

    public Page<T> pageImpl() {
        return new PageImpl<>(getContent(), new PageRequest(getNumber(),
                getSize(), getSort()), getTotalElements());
    }
}

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