javaspringrestspring-dataspring-data-rest

How to consume Page<Entity> response using Spring RestTemplate


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

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

Then i have a controller:

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

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)

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


Solution

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

    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>>() {}
    

    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>>() {}
    

    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());
        }
    }