Passing Java Object via remote transport in Spring XD

Question

If the message payload passed from one "filter" to the next "filter" in Spring XD stream is a custom Java class instance, I suppose some kind of serialization mechanism is required if the "pipe" in between is a remote transport.

1. What kind of "serialization"/"transformation" is available in Spring XD for this case?
2. Will Java serialization work for this case? And if the custom class is serializable, will Spring XD automatically serialise/deserialize the object, or we still need to give some hints in the stream definition/module definition?

Thanks, Simon

Answer 1

XD uses Kryo serialization with remote transports. Java.io.serialization would work in theory, however we don't want to assume that payload types implement java.io.Serializable. Also, I personally don't see any advantage in choosing Java serialization automatically over Kryo if the payload is Serializable. Java serialization is supported via Spring XD's type conversion.

You should be able to create a stream containing something like:

filter1 --outputType=--application/x-java-serialized-object | filter2 --input-type=my.custom.SerializablePayloadType

In this case, the type conversion will use Java serialization before hitting the transport. The message bus will detect that the payload is a byte array and will send it directly to the next module as is. The message containing the bytes will set the content-type header to the declared outputType so that it can be deserialized using Java serialization by the inbound converter.

The above requires that the payload implements Serializable. Also custom payload types must be included in Spring XD's class path, i.e., add a jar to xd/lib on each installed container.