如何使用Future<T>返回异步结果AsyncResult<T>?

Question

继承关系如下：

class AsyncResult<V> implements ListenableFuture<V>

interface ListenableFuture<T> extends Future<T>

interface Future<T>

我使用AsyncResult如下：

@Async
public AsyncResult<Integer> asyncMul10(int base){
    base = base * 10;
    return new AsyncResult<>(base);
}

按以下步骤获取asyncMul10():

Future<Integer> future10 =asyncHandle.asyncMul10(base);

在运行到这行代码时会抛出异常。

java.lang.ClassCastException: org.springframework.util.concurrent.ListenableFutureTask cannot be cast to org.springframework.scheduling.annotation.AsyncResult

我不理解为什么子类不能转换为父类。

所有代码如下：

MainServiceImpl Service:

@Service
public class MainServiceImpl implements IMainService {
    @Autowired
    private IAsyncHandle asyncHandle;
    @Override
    public String async(int base) throws InterruptedException, ExecutionException {
        Integer mul10;
        Future<Integer> future10 =asyncHandle.asyncMul10(base);
        while (true){
            if(future10.isDone()){
                mul10=future10.get();
                break;
            }
        }
        return "Mul 10 = "+mul10;
    }
}

IAsyncHandle Interface:

public interface IAsyncHandle {
    AsyncResult<Integer> asyncMul10(int base) throws InterruptedException;
}

AsyncHandleImpl Component class
@Component
public class AsyncHandleImpl implements IAsyncHandle {
    @Override
    @Async
    public AsyncResult<Integer> asyncMul10(int base){
        base = base * 10;
        return new AsyncResult<>(base);
    }
}

以下是异常堆栈跟踪：

java.lang.ClassCastException: org.springframework.util.concurrent.ListenableFutureTask cannot be cast to org.springframework.scheduling.annotation.AsyncResult
    at com.sun.proxy.$Proxy61.asyncMul10(Unknown Source) ~[na:na]
    at cn.zora.springdemo.service.impl.MainServiceImpl.async(MainServiceImpl.java:33) ~[classes/:na]
    at cn.zora.springdemo.controller.MainController.async(MainController.java:28) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_231]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_231]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_231]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_231]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1591) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_231]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_231]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_231]

BTW,

at cn.zora.springdemo.service.impl.MainServiceImpl.async(MainServiceImpl.java:33) ~[classes/:na]

是

Future<Integer> future10 =asyncHandle.asyncMul10(base);

- Zorazora

---

这对您有帮助吗？：https://dev59.com/6Hvaa4cB1Zd3GeqPGKkq#21313963 - Sid

异常与您发布的代码行无关，而是由您代码中的另一行引发的。 - Mạnh Quyết Nguyễn

你能显示完整的堆栈跟踪并指出异常发生的行吗？因为我不认为这是Future<Integer> future10 =asyncHandle.asyncMul10(base);这一行引起的。 - Sam Orozco

它并不是将子类转换为父类。它是在说无法将 ListenableFutureTask 转换为 AsyncResult。它们都实现了 ListenableFuture，但似乎没有其他关联。 - Scratte

我不明白为什么子类不能转换为父类。ListenableFutureTask 类继承自 FutureTask，而 AsyncResult 类则继承自 java.lang.Object。那么 ListenableFutureTask 如何成为 AsyncResult 的子类呢？ - Abra

ListenableFutureTask 是 AsyncResult 的父类。 - Zorazora

Answer 1

问题出在这一行代码上。

@Async
public AsyncResult<Integer> asyncMul10(int base){
    base = base * 10;
    return new AsyncResult<>(base);
}

将返回类型从AsyncResult更改为Future，就可以解决问题。

@Async
public Future<Integer> asyncMul10(int base){
    base = base * 10;
    return new AsyncResult<>(base);
}

- shrinidhi joshi