网关和聚合器-相关策略错误

我必须使用spring集成访问外部服务。这个过程是(1)我必须通过一个id来获取基本信息(2)使用步骤1中的基本信息,我需要访问更多的服务并将信息合并到singlr对象中。 集成图: 输入:通道1输出到:通道1输出 我有一个接收者列表路由器,它将消息放入通道2和通道3。

channel2和channel3的输出通道使用xml xpath转换器 输出到通道4

<int:aggregator id="aggregatorChannel"      
                    correlation-strategy-expression="headers['jms_messageId']"  
                    release-strategy-expression="size() == 2" method="mergeVO"
                    input-channel="channel4" output-channel="dest-channel">
            <bean class="n.b.lbr.eai.vo.PojoAggregator"></bean>
    </int:aggregator>

这是个错误。

java.lang.IllegalStateException: Null correlation not allowed.  Maybe the CorrelationStrategy is failing?
        at org.springframework.util.Assert.state(Assert.java:70) ~[spring-core-4.3.8.RELEASE.jar:4.3.8.RELEASE]
        at org.springframework.integration.aggregator.AbstractCorrelatingMessageHandler.handleMessageInternal(AbstractCorrelatingMessageHandler.java:385) ~[spring-integration-core-4.3.9.RELEASE.jar:4.3.9.RELEASE]

我确实看到一些关于这个主题的帖子,但是我不知道如何解决下面的错误

{
    "timestamp": 1533137160301,
    "status": 500,
    "error": "Internal Server Error",
    "exception": "java.lang.IllegalStateException",
    "message": "Null correlation not allowed.  Maybe the CorrelationStrategy is failing?",
    "path": "/w/b/search/11223"
}

请建议,如果这是一个设计问题或如何解决这个问题

Eddi1: 下面的散点集有效吗?

<bean id="messageStore" class="org.springframework.integration.store.SimpleMessageStore"/>
    <int:scatter-gather id="scatterGather2" input-channel="drBInputChannel" gather-channel="gatherChannel" gather-timeout="5000">
        <int:scatterer id="myScatterer" apply-sequence="true">
            <int:recipient channel="bserviceInputChannel"/>
            <int:recipient channel="aserviceInputChannel"/>
        </int:scatterer>
        <int:gatherer id="myGatherer" 
                **??**
                message-store="messageStore"
                correlation-strategy=**??**
                release-strategy-expression="size() == 2"
                >
        <bean class="nd.wbr.eai.vo.PojoAggregator"></bean>
        </int:gatherer>
    </int:scatter-gather>

我需要帮助来转换成xml并在上面使用

@Bean
public MessageHandler gatherer() {
    return new AggregatingMessageHandler(
            ***new ExpressionEvaluatingMessageGroupProcessor("^[payload gt 5] ?:-1D"),***
            new SimpleMessageStore(),
            ***new HeaderAttributeCorrelationStrategy(
                   IntegrationMessageHeaderAccessor.CORRELATION_ID),***
            new ExpressionEvaluatingReleaseStrategy("size() == 2"));
}