空指针异常 - 依赖注入 - Google Guice

Question

我在 Jersey 的 reader 拦截器中注入依赖项时收到 NullPointerException，我创建该拦截器是为了拦截特定的传入请求。

这是我创建的 ReaderInterceptor 的代码，我试图在其中注入所需的依赖项。

public class RegisterServiceInterceptor implements ReaderInterceptor {

    @Inject
    private CustomerBackendManager customerBackendManager;

    public static final Logger LOGGER = LoggerFactory.getLogger(RegisterServiceInterceptor.class);

    @Override
    public Object aroundReadFrom(ReaderInterceptorContext context) throws IOException, WebApplicationException {
        InputStream is = context.getInputStream();
        String body = new BufferedReader(new InputStreamReader(is)).lines().collect(Collectors.joining("\n"));
        ObjectMapper mapper = new ObjectMapper();
        try {
            SampleObject sampleObject = mapper.readValue(body, SampleObject.class);
            customerBackendManager.createDatabase(sampleObject.getDatabaseName());
        } catch (JsonGenerationException | JsonMappingException e) {
            LOGGER.info(e.getMessage());
        }
        InputStream in = new ByteArrayInputStream(body.getBytes(StandardCharsets.UTF_8));
        context.setInputStream(in);
        return context.proceed();
    }

}

我在 customerBackendManager.createDatabase(...); 行收到 NPE。依赖项未注入此 class。

我已将此依赖项的配置定义为

public class ExampleAddonMicroserviceModule extends AbstractModule
        implements ConfigurationAwareModule<ExampleAddonMicroserviceConfiguration> {

    @Provides
    @Singleton
    public CustomerBackendManager customerBackendManager(DBI dbi, Injector injector) {
        CustomerBackendManager manager = dbi.onDemand(CustomerBackendManagerImpl.class);
        injector.injectMembers(manager);
        return manager;
    }

    @Provides
    @Singleton
    public RegisterServiceInterceptor registerServiceInterceptor(DBI dbi, Injector injector) {
        RegisterServiceInterceptor manager = dbi.onDemand(RegisterServiceInterceptor.class);
        injector.injectMembers(manager);
        return manager;
    }
}

我需要添加什么额外的配置才能将此依赖项添加到此 class？

Answer 1

我找到了解决这个问题的方法。

问题是 Jersey 需要配置中的拦截器 class，它需要在满足拦截条件时调用它，这导致 RegisterServiceInterceptor class 被初始化两次。因此，RegisterServiceInterceptor class.

中的 NPE

我在单独的配置文件中定义了该配置

@Provider
public class ResourceFilteringConfiguration implements DynamicFeature {

    @Override
    public void configure(ResourceInfo resourceInfo, FeatureContext context) {
        if (RegistrationService.class.equals(resourceInfo.getResourceClass())
                && resourceInfo.getResourceMethod().getName().equals("register")) {
            context.register(RegisterServiceInterceptor.class);
        }
    }

}

在 context.register(RegisterServiceInterceptor.class); 行中，我传递了 RegisterServiceInterceptor class 本身，这导致它在达到依赖项配置（问题中提到的）之前进行初始化。所以，这个拦截器被初始化了两次，这导致了这个问题。我把配置文件代码改成了

@Provider
public class ResourceFilteringConfiguration implements DynamicFeature {

    @Inject
    private RegisterServiceInterceptor registerServiceInterceptor;

    @Override
    public void configure(ResourceInfo resourceInfo, FeatureContext context) {
        if (RegistrationService.class.equals(resourceInfo.getResourceClass())
                && resourceInfo.getResourceMethod().getName().equals("register")) {
            context.register(registerServiceInterceptor);
        }
    }

}

您一定已经注意到，我所做的更改是将 RegisterServiceInterceptor 的对象传递给配置，它开始正常工作。

空指针异常 - 依赖注入 - Google Guice

Null Pointer Exception - Dependency Injection - Google Guice

java

dependency-injection

jax-ws

guice