java Spring自动添加“XTotalCount”头

Question

我正在为我的Web应用程序使用“rest上的管理员”UI，它有下一个限制：

Note: The jsonServer REST client expects the API to include a X-Total-Count header in the response to GET_LIST calls. The value must be the total number of resources in the collection. This allows admin-on-rest to know how many pages of resources there are in total, and build the pagination controls.

我通过将X-Total-Count头添加到手动返回REST端点的列表中解决了此问题，如下所示： response.addHeader("X-Total-Count", String.valueOf(outputList.size()));

但我想知道：是否有一些优雅的方式可以在春天自动完成？我的意思是，当某个端点返回JSON列表时，自动添加具有适当值的头

Answer 1

因为从页面中可以得到全部元素。所以我给ResponseEntity添加了标题

@GetMapping(value = POSTS, headers = "Accept=application/json")
public ResponseEntity<?> getListPost(@RequestParam(required = false, defaultValue = "0") Integer page, @RequestParam(required = false, defaultValue = "25") Integer size) {
    // Create pageable
    Pageable pageable = new PageRequest(page, size);
    Page<Post> pagePost = postService.getPagePost(pageable);

    HttpHeaders headers = new HttpHeaders() {
        {
            add("Access-Control-Expose-Headers", "Content-Range");
            add("Content-Range", String.valueOf(pagePost.getTotalElements()));
        }
    };
    //        return new ResponseEntity<>(new CommonResponseBody("OK", 200, postList), HttpStatus.OK);
    return new ResponseEntity<>(new CommonResponseBody("OK", 200, new LinkedHashMap() {
        {
            put("data", pagePost.getContent());
        }
    }), headers, HttpStatus.OK);
}

getPagePost是一种服务方法，它在存储库中使用PageFindall（Pageable Pageable）

注意：如果内容范围不适合您，请将其更改为X-Total-Count

Answer 2

是的，有！（如果您使用的是spring 4.1或更高版本）

它被称为ResponseBodyAdvice，它使您能够拦截调用（就在编写响应并允许访问原始http响应之前）

基本上，您需要实现如下控制器建议：

@ControllerAdvice
public class ResourceSizeAdvice implements ResponseBodyAdvice<Collection<?>> {

    @Override
    public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
        //Checks if this advice is applicable. 
        //In this case it applies to any endpoint which returns a collection.
        return Collection.class.isAssignableFrom(returnType.getParameterType()); 
    }

    @Override
    public Collection<?> beforeBodyWrite(Collection<?> body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
        response.getHeaders().add("X-Total-Count", String.valueOf(body.size()));
        return body;
    }
}

Answer 3

如果您不想要响应中元素的总数，而是想要相应的JPA方法PagingAndSortingRepository中实体的总数，您可以做一些对分页应用程序有用的事情：）

受Bohdan的答案启发（https://stackoverflow.com/a/44376133/986160）

@ControllerAdvice
public class ResourceSizeAdvice implements ResponseBodyAdvice<Page<?>> {

    @Override
    public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
        //Checks if this advice is applicable.
        //In this case it applies to any endpoint which returns a page.
        return Page.class.isAssignableFrom(returnType.getParameterType());
    }

    @Override
    public Page<?> beforeBodyWrite(Page<?> page, MethodParameter methodParameter, MediaType mediaType, Class<? extends HttpMessageConverter<?>> aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {
        serverHttpResponse.getHeaders().add("X-Total-Count",String.valueOf(page.getTotalElements()));
        return page;
    }

}

确保调用默认方法的可分页版本，如它返回Page而不是List：

repository.findAll(new PageRequest(0,100));

如果不使用存储库，则必须执行两个查询： Select * from ...和 Select count(*) from ... 并返回一个Wrapper，其中包含结果列表的内容，以及来自count的总数的总和。然后，您可以更改@ControllerAdvice类，以期望您的Wrapper，并从中获取总数，然后将其放在标题中