从另一个类调用方法时，DiscoveryClient上的java.lang.NullPointerException

Question

当我通过浏览器调用方法本身时，它正在工作，并且得到了预期的JSON 。 因此，该方法有效，并且请求的服务已注册。

    @RequestMapping("/getArticle/{articleId}")
public String getArticle(@PathVariable("articleId") Integer articleId) {
    // {"articleId":47,"name":"test","price":5.0}
    List<ServiceInstance> instances = 
discoveryClient.getInstances("articlemicroservice");    //null when calling 
    ServiceInstance serviceInstance = instances.get(0);
    String baseUrl = serviceInstance.getUri().toString();

    baseUrl = baseUrl + "/db/find/" + articleId.toString();

    System.out.println("BASEURL: " + baseUrl);

    RestTemplate restTemplate = new RestTemplate();
    ResponseEntity<String> response = null;

    try {
        response = restTemplate.exchange(baseUrl, HttpMethod.GET, 
getHeaders(), String.class);
    } catch (Exception ex) {
        System.out.println(ex);
    }
    // {"articleId":47,"name":"test","price":5.0}
    String articleEntity = response.getBody().toString();
    System.out.println("articleEntity: " + articleEntity);
    return articleEntity;
}

当我从另一个类（位于同一项目中）调用该方法时，我得到了NullPointerException 。

    @GetMapping(path = "/addCartItemToCart/{cartId}/{articleId}/{quantity}")
public @ResponseBody String addCartItemToCart(@PathVariable("cartId") 
Integer cartId,
        @PathVariable("articleId") Integer articleId, 
@PathVariable("quantity") Integer quantity) {

    ArticleMicroserviceRestConnectorRequester n = new 
ArticleMicroserviceRestConnectorRequester();

    String article = n.getArticle(articleId); //calling the method here
    JSONObject json = new JSONObject(article);
    CartItemEntity cartItemEntity = new CartItemEntity();
    cartItemEntity.setArticleId(json.getInt("articleId"));
    cartItemEntity.setQuantity(quantity);
    cartItemEntity.setCartItemId(cartId);
    CartEntity cartEntity = cartRepository.findById(cartId).get();
    cartEntity.addCartItem(cartItemEntity);
    cartEntity.setNumberOfCartItems(cartEntity.getNumberOfCartItems() + 
 cartItemEntity.getQuantity());
    cartRepository.save(cartEntity);
    return "Saved";     
    }

例外：

java.lang.NullPointerException: null at de.leuphana.jee.connector.jpa.behaviour.ArticleMicroserviceRestConnectorRequester.getArticle(ArticleMicroserviceRestConnectorRequester.java:44) ~[classes/:na] ...

Answer 1

在addCartItemToCart您创建的新实例ArticleMicroserviceRestConnectorRequester 。 它不是由Spring管理的，因此discoveryClient没有自动连接，它为null。

您必须将ArticleMicroserviceRestConnectorRequester注入其他类。 因此，您将获得一个由Spring管理的实例，该实例应具有自动接线/注入的discoveryClient 。