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

Question

When I am calling the method itself through the browser it's working and I am getting the expected JSON . So the method is working and the requested service is registered.

    @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;
}

When I am calling the method from another class (which is located in the same project) I am getting a 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";     
    }

Exception:

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

Answer 1

In addCartItemToCart you create a new instance of ArticleMicroserviceRestConnectorRequester . It is not managed by Spring so discoveryClient is not autowired, it is null.

You have to inject ArticleMicroserviceRestConnectorRequester into your other class. Thus you will get an instance which is managed by Spring and should have autowired/injected discoveryClient .