Question

从请求范围的线程中，CompletableFuture必须由执行程序中运行的任务完成。提供的供应商使用特定于域的服务MessageService，该服务是会话范围的。该服务由Guice注入。

public class MessageProcessingPage {
    private MessageService messageService;

    @Inject
    public MessagProcessingPage (MessageService messageService) {
        this.messageService = messageService;
    }

    // Called by request scoped thread.
    public void onProcessMessagesButton () {
        ExecutorService executorService = Executors.newFixedThreadPool(3);
        CompletableFuture.supplyAsync(
        // Called from a thread from the threadpool.
        () -> {return messageService.retrieveMessageMetadataSet(x, y);}
        , executorService);

        ...

    }

    ...
}

MessageService有一个（会话作用域）MessageRestClient被注入。

@SessionScoped
public class MessageService {
    private MessageRestClient messageRestClient;

    @Inject
    public MessageRestClient (MessageRestClient messageRestClient) {
        this.messageRestClient = messageRestClient;
    }

    public MessageMetaDataSet retrieveMessageMetadataSet(x, y) {
        List<MessageMetaData> listOfMetaData = messageRestClient.retrieve(x, y, z);
        ...
    }

    ...
}

@SessionScoped
public class MessageRestClient {
    ...
}

当Guice尝试注入MessageRestClient时会遇到麻烦。

java.util.concurrent.CompletionException: com.google.inject.ProvisionException: Unable to provision, see the following errors:

1) Error in custom provider, com.google.inject.OutOfScopeException: Cannot access scoped [MessageRestClient]. Either we are not currently inside an HTTP Servlet request, or you may have forgotten to apply com.google.inject.servlet.GuiceFilter as a servlet filter for this request.

我在ServletScopes中了解了一种方法：public static <T> Callable<T> transferRequest(Callable<T> callable) 但是我没有看到使用它的方法，因为没有Callables可以参与比赛。你能帮我解决一下吗？

Answer 1

在Guice中处理servlet请求时，GuiceFilter已经负责设置正确的上下文（通过ThreadLocal），以便它可以知道您在哪个请求中，因此，适当地应用范围。使用SessionScope注释的类的实例实际上是代理，可以从Guice访问该请求和会话信息并采取相应的行动。

您发送到CompletableFuture的任务在Guice控件的单独线程中运行。 ThreadLocal可以从Guice获取该信息，因此没有Request，因此，没有Session或[SessionScope信息，这意味着什么，没有Callable<MessageMetaDataSet> c = ServletScopes.transferRequest( () -> messageService.retrieveMessageMetadataSet(x, y)); CompletableFuture.supplyAsync( () -> c.call() , executorService); 。由于代理无法了解会话的任何信息，因此会引发您遇到的错误。

ServletScopes.transferRequest方法应该注入所需的信息，以便范围有效。应该这样工作（但从未尝试过）：

Profile

Answer 2

尽早尝试：Guice @Inject工作正常：



    import java.util.concurrent.CompletableFuture;

    public class AsyncFire {

        public static > void execAsync(Class asyncClass) {
            T asyncInstance = AsyncInjector.getInjector().getInstance(asyncClass); //magic
            CompletableFuture completableFuture = CompletableFuture.supplyAsync(asyncInstance); //business logic
            completableFuture.exceptionally(asyncInstance); //if error
            completableFuture.thenAccept(asyncInstance); //if success
        }

    }



    public class ExampleAsync extends Async {

        @Inject //it works
        private EntityManager entityManager;

        @Inject //it works
        private DAO dao; //your

    }



    import java.util.function.Consumer;
    import java.util.function.Function;
    import java.util.function.Supplier;

    public abstract class Async implements Supplier, Consumer, Function {
        //...
    }



    import com.google.inject.Guice;
    import com.google.inject.Injector;
    import com.google.inject.persist.PersistService;

    public final class AsyncInjector {

        private static Injector injector = null; 

        public static Injector getInjector() {
            if (injector == null) {
                synchronized (AsyncInjector.class) {
                    if (injector == null) {
                        injector = Guice.createInjector(new MyGuiceModule()); //your guice module
                        PersistService service = injector.getInstance(PersistService.class);
                        service.start();
                    }
                }
            }
            return injector;
        }

    }

希望这有助于某人！

Guice在执行CompletableFuture时抛出OutOfScopeException

2 个答案: