How to consume Page<Entity> response using Spring RestTemplate

Question

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?

Answer 1

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());     } }