@GetMapping
    public ShenyuAdminResult getReceivers(@RequestParam @NotNull final Integer currentPage,
                                          @RequestParam @NotNull final Integer pageSize,
                                          @Valid @Existed(message = "namespaceId is not existed",
                                                  provider = NamespaceMapper.class) final String namespaceId
    ) {
        CommonPager<AlertReceiverDTO> commonPager = alertReceiverService.listByPage(new AlertReceiverQuery(new PageParameter(currentPage, pageSize), namespaceId));
        return ShenyuAdminResult.success(commonPager);
    }
query receiver.
@param currentPage current page
@param pageSize page size
@param namespaceId namespaceId.
@return receiver
shenyu-admin/src/main/java/org/apache/shenyu/admin/controller/AlertReceiverController.java