Question

我目前有以下Camel路线：

<camelContext id="my-camel-context" xmlns="http://camel.apache.org/schema/spring">
    <propertyPlaceholder id="envProps" location="classpath:myapp.properties" />
    <route id="my-camel-route"> 
        <from uri="{{start.uri}}"/>

        <setHeader headerName="id">
            <constant>1</constant>
        </setHeader>

        <to uri="bean:preProcessor?method=process" />

        <aggregate strategyRef="myAggregationStrategy" completionSize="1">
            <correlationExpression> 
                <simple>${header.id} == 1</simple> 
            </correlationExpression>
            <to uri="bean:postProcessor?method=process" /> 
        </aggregate> 

        <to uri="bean:mailer?method=process" /> 
    </route> 
</camelContext>

<bean id="myAggregationStrategy" class="com.me.myapp.MyAggregationStrategy" />
<bean id="postProcessor" class="com.me.myapp.PostProcessor" />
<bean id="mailer" class="com.me.myapp.Mailer" />

目前，我并没有真正汇总任何有意义的内容（completionSize=1），我只是在测试AggregationStrategy。这是我的策略：

public class MyAggregationStrategy implements AggregationStrategy {
    @Override
    public Exchange aggregate(Exchange aggregatingExchange, Exchange incomingExchange) {
        AppPayload payload = null;

        if(aggregatingExchange == null)
            payload = new AppPayload(); // This should prevent it from being NULL below in PostProcessor...
        else
            payload = (AppPayload)incomingExchange.getIn().getBody();

        payload.setCargo((Order)incomingExchange.getIn().getBody());

        if(aggregatingExchange == null) {
            incomingExchange.getIn().setBody(payload);
            return incomingExchange;
        }
        else
            return aggregatingExchange;
    }
}

还有我的postProcessor bean：

public class PostProcessor implement Processor {
    @Override
    public void process(Exchange exchange) {
        try {
            System.out.println("In PostProcessor...");
            AppPayload payload = (AppPayload)exchange.getIn().getBody();
            System.out.println("\t...payload acquired...");

            if(payload == null)
                System.out.println("Payload is NULL.");
        } catch(Throwable throwable) {
            System.out.println(ExceptionUtils.getFullStackTrace(throwable));
        }
    }
}

当我运行此代码时，我看到来自preProcessor bean的日志消息，表明它正在正确执行。我还看到MyAggregationStrategy正确地“聚合”了该消息，然后在第一条消息到达后将其传递给postProcessor（再次，因为completionSize=1）。但是，我在postProcessor中获得了以下输出：

In PostProcessor...
    ...payload acquired...
Payload is NULL.

任何人都可以看到为什么payload为NULL？它是否应该在MyAggregationStrategy内初始化？！？我很乐意发布更多代码，但我认为这源于我错误地使用AggregationStrategy API。

Answer 1

我相信你对aggregatingExchange和incomingExchange感到困惑。你能试试这个：

public class MyAggregationStrategy implements AggregationStrategy {
    @Override
    public Exchange aggregate(Exchange aggregatingExchange, Exchange incomingExchange) {
        AppPayload payload = null;

        if(aggregatingExchange == null) {
        payload = new AppPayload(); // This should prevent it from being NULL below in PostProcessor...
        } else {
            payload = (AppPayload)aggregatingExchange.getIn().getBody();
        }

        payload.setCargo((Order)incomingExchange.getIn().getBody());

        if(aggregatingExchange == null) {
            incomingExchange.getIn().setBody(payload);
            return incomingExchange;
        } else {
            return aggregatingExchange;
        }
    }
}

Answer 2

添加@hveiga已经提到的内容。我有一个类似的问题，我通过添加标题到我的消息解决。但是在您的情况下，我发现您没有使用拆分器，并且您已经定义了标头。因此，从Clauss Ibssen得到的一条信息是第一次时间交换是空的，我们需要检查空对象。

有关详细说明，请参阅此处 - Apache Camel - Split and aggregate - Old Exchange is always null

在此处跟踪完整说明 - http://camel.465427.n5.nabble.com/Split-and-Aggregate-Old-Exchange-is-null-everytime-in-AggregationStrategy-td5746365.html

Camel AggregationStrategy生成NULL实体消息

2 个答案: