apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/controller/ConfigFileController.java/ConfigFileController/queryConfigAsJson
class ConfigFileController:  @GetMapping(value = "/json/{appId}/{clusterName}/{namespace:.+}")
  public ResponseEntity<String> queryConfigAsJson(@PathVariable String appId,
                                                  @PathVariable String clusterName,
                                                  @PathVariable String namespace,
                                                  @RequestParam(value = "dataCenter", required = false) String dataCenter,
                                                  @RequestParam(value = "ip", required = false) String clientIp,
                                                  @RequestParam(value = "label", required = false) String clientLabel,
                                                  HttpServletRequest request,
                                                  HttpServletResponse response) throws IOException {

    String result =
        queryConfig(ConfigFileOutputFormat.JSON, appId, clusterName, namespace, dataCenter,
            clientIp, clientLabel, request, response);

    if (result == null) {
      return NOT_FOUND_RESPONSE;
    }

    return new ResponseEntity<>(result, jsonResponseHeaders, HttpStatus.OK);
  }