I'm working on https://issues.apache.org/jira/browse/BEAM-5638 to add exception handling options to single message transforms in the Java SDK.
MapElements' via() method is overloaded to accept either a SimpleFunction, a SerializableFunction, or a Contextful, all of which are ultimately stored as a Contextful where the mapping functionis expected to have signature: OutputT apply(InputT element, Context c) throws Exception; So Contextful.Fn allows throwing checked exceptions, but neither SerializableFunction nor SimpleFunction do. The user-provided function has to satisfy the more restrictive signature: OutputT apply(InputT input); Is there background about why we allow arbitrary checked exceptions to be thrown in one case but not the other two? Could we consider expanding SerializableFunction and SimpleFunction to the following?: OutputT apply(InputT input) throws Exception; This would, for example, simplify the implementation of ParseJsons and AsJsons, where we have to catch an IOException in MapElements#via only to rethrow as RuntimeException.
