我的Spring集成流的一些问题

Question

我使用的是带有spring Integration 5.3.0的spring boot 2.3.0版本，不知何故，我无法让下面的代码正常工作。应用程序启动，没有错误，但当控制到NextChannelFlow（）方法时，什么也没有发生或打印。谁能告诉我我错过了什么。任何帮助都很感激。谢了。

@Configuration
@EnableIntegration
@EnableRetry
    Class MyIntegrationFlow
    .
    .

    @Bean
    public IntegrationFlow upstreamFlow(){
    return IntegrationFlows.from(someChannel())
    .handle(srcDirectory(), "receive")                               
    .filter(onlyCsvfiles())                    
    .handle(targetDirectory())// returns a FileWritingMessageHandler
    .channel(nextChannel())     //this is downstream                            
    .get();
    }

@Bean
    public MessageHandler targetDirectory() throws IOException {
        FileWritingMessageHandler handler = new FileWritingMessageHandler(targetFolder.getFile());
        handler.setExpectReply(false);
        return handler;
    }   

    @Bean
    public DirectChannel nextChannel(){
    return new DirectChannel();
    }

    @Bean
    public IntegrationFlow nextChannelFlow() {
//the below is that last line that gets printed in console. After this line, nothing gets printed and I see no errors too.
        System.out.println("inside nextChannel method ");

        return IntegrationFlows.from (nextChannel()) 
                .handle((GenericHandler<String>) (payload, headers) -> {
                    System.out.println("inside handle 1");
                    callSomeMethod();
                    System.out.println("inside handle 2");
                    return payload;                 
                })
                .log(Level.INFO, new LiteralExpression("came out of handle.")) //was trying to see if I can see any logs/errors at this line , but nothing displayed.
                .channel(checkXFBFlowChannel())//control doesn't go to this channel as well.
                .get();
    }   

    @Retryable(value={IllegalStateException.class}, maxAttempts=5,backoff=@Backoff(delay=3000))
    public void callSomeMethod() {
        System.out.println("simulate sample retry method");        
        throw new IllegalStateException() ;                  
    }

Answer 1

.handle(returns MessageHandler)

如果它是一个普通的MessageHandler，那么在它之后就不会发生任何事情。它不返回任何东西（void），因此在此之后没有回复继续流。请考虑使用句柄(GenericHandler)。