App properties in Spring Cloud Data Flow application

Question

Based on the documentation for Spring Cloud Data Flow (SCDF) only properties that are prefixed by either "deployed." or "app." are considered when deploying an application (be it a source, processor or sink) as part of a stream.

However, I've noticed that besides the prefix, all the properties must be provided as "strings", no matter what their original type is; otherwise, they are simply discarded by SCDF as per this line of code:

    propertiesToUse = DeploymentPropertiesUtils.convert(props);

which does this:

public static Map<String, String> convert(Properties properties) {
    Map<String, String> result = new HashMap<>(properties.size());
    for (String key : properties.stringPropertyNames()) {
        result.put(key, properties.getProperty(key));
    }
    return result;
}

As you can see from the snippet above, it only considers "stringPropertyNames" which filters out anything that is not provided as a "String".

I presume this behaviour is intentional, but why? Why not just pick up all the properties defined by the user with the proper prefix?

Thanks for your support.

Answer 1

All the deployment properties are expected to be of Map<String, String> based on the contract set by the deployer SPI.

I believe one of the reasons is to have String key, values being passed to target deployment platform without serialization/de-serialization hurdle. and, using String values is similar to how one could set those key, value properties as environment variables (for example) in the target deployment platform.