Apache Camel auto type convert Protobuf in routes

Question

I have a topic set up with using Camel and ActiveMQ which receives messages as a byte array of a protobuf.

The receive route looks like this:

    <route>
        <from uri="jmsComponent:topic:{{heartbeat}}" />
        <unmarshal>
            <protobuf instanceClass="protobuf.HeartbeatProto" />
        </unmarshal>
        <to uri="bean:heartbeatConsumer" />
    </route>

The heartbeatConsumer only has one method that takes the POJO version of a Heartbeat. In order for this to work, I have a type converter that converts to/from POJO to protobuf.

This works very well and Camel is able to take the byte array and pass it to the heartbeatConsumer as a POJO.

My issue comes with the sender. I have my sending route setup as:

    <route>
        <from uri="quartz2://heartbeatJob?cron=0/30+*+*+*+*+?" />
        <to uri="bean:heartbeat?method=sendHeartbeat" />
        <marshal>
            <protobuf instanceClass="protobuf.HeartbeatProto" />
        </marshal>
        <to uri="jmsComponent:topic:{{heartbeat}}" />       
    </route>

It gives me the exception: 'java.lang.ClassCastException: protobuf.HeartbeatProto cannot be cast to com.google.protobuf.Message'

Why would it be able to automatically type converter in the receive route, but not in the sending route?

Answer 1

Marshalling Java classes to a protobuf payload only works correctly with Java classes implementing the com.google.protobuf.Message interface as can be seen digging into the source code of org.apache.camel.dataformat.protobuf.ProtobufDataFormat ( here ):

public void marshal(Exchange exchange, Object graph, OutputStream outputStream) throws Exception {
    ((Message)graph).writeTo(outputStream);  // <- here the ClassCastException occurs!
}

As stated at the Camel doc , you should start with a .proto definition file that is compiled with protoc --java_out=. ./protobuf.HeartbeatProto protoc --java_out=. ./protobuf.HeartbeatProto to a Java class implementing the desired interface.