Spring 在單元測試中啟動 @Autowired 返回 NullPointerException

Question

我有一個用@service 注釋的類（HttpHandler）。 我正在為此服務 class 編寫單元測試用例。 我在測試 class 中使用了@Autowired 注釋來獲取服務的 object。 但是，當我運行單元測試時，它返回 NullPOinterException。 有人能幫我嗎？

下面是服務 class 的代碼：

@Service
public class HttpHandler {

    private static final Logger logger = LoggerFactory.getLogger(HttpHandler.class);

    /**
     * Build the request and Perform Http Get request with headers
     * @param url
     * @param httpHeaders
     * @param responseClass
     * @param <T>
     * @param <R>
     * @return
     */
    public <T,R> ResponseEntity<T> sendPost(String url, HttpHeaders httpHeaders, R requestBody, Class<T> responseClass) {
        //create an instance of rest template
        RestTemplate restTemplate = new RestTemplate();
        HttpEntity<R> entity = new HttpEntity<R>(requestBody, httpHeaders);
        logger.info("POST request to " + url + " with body: " + JsonUtil.jsonizeExcludeNulls(requestBody));
        //make an HTTP POST request with headers
        ResponseEntity<T> response = restTemplate.exchange(url, HttpMethod.POST, entity, responseClass);
        logger.info("POST" + url + ": " + JsonUtil.jsonize(response));
        return response;
    }
}

我正在為 POST 調用編寫單元測試用例。 下面是 POST 調用的單元測試 public class HttpHandlerTest {

@Autowired
HttpHandler httpHandler;

@Test
public void testSuccessPostUser() throws Exception{

    String baseUrl = "http://localhost:8080/users";
    List<String> messages = new ArrayList<>();
    messages.add("Hi");

    User user = new User();
    user.setId(1);
    user.setName("John");
    user.setAge(22);
    user.setMessages(messages);

    HttpHeaders httpHeaders = new HttpHeaders();
    httpHeaders.setContentType(MediaType.APPLICATION_JSON);
    httpHeaders.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));

    HttpEntity<User> httpEntity = new HttpEntity<>(user, httpHeaders);

    ResponseEntity<User> actual = httpHandler.sendPost(baseUrl, httpHeaders, user, User.class);

    //verify request succeed
    assertEquals(HttpStatus.CREATED, actual.getStatusCode());
    assertEquals(201, actual.getStatusCodeValue());
    assertTrue(actual.toString().contains("id"));
}

}

它給出以下錯誤：

java.lang.NullPointerException
    at com.xyz.provisioning.xyz.utils.HttpHandlerTest.testSuccessPostUser(HttpHandlerTest.java:41)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:686)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)

Answer 1

如果使用 JUnit5，則在 class 上方添加@ExtendWith(SpringExtension.class) ，如果使用 JUnit4，則添加 @RunWith(SpringRunner.class @RunWith(SpringRunner.class) 。

Answer 2

對於 Junit 5（如評論中所述），您只需在測試 class 頂部添加@SpringBootTest 。

@SpringBootTest
class HttpHandlerTest{
// ...
}

您不需要添加@ExtendWith(SpringExtension.class)因為由注解@SpringBootTest自動導入。

要為 Junit 4 獲得相同的結果：

@RunWith(SpringRunner.class)
@SpringBootTest
class HttpHandlerTest{
// ...
}