Payload and logging
A Payload interface is used for implementing a TrackerPayload and SelfDescribingJson, but accordingly, can be used to implement your own Payload class if you choose.
Tracker Payload​
A TrackerPayload is used internally within the Java Tracker to create the tracking event payloads that are passed to an Emitter to be sent accordingly. It is essentially a wrapper around a LinkedHashMap<String, String> and does basic validation to ensure all key-value pairs are valid non-null and non-empty Strings.
SelfDescribingJson​
A SelfDescribingJson is used primarily to ease construction of self-describing JSON objects. It is a wrapper around a LinkedHashMap<String, Object> and will only ever contain two key-value pairs. A schema key with a valid schema value and a data key containing a Map of key-value pairs.
This is used under the hood but is also useful for to know about when attaching custom contexts to events or creating Unstructured events.
Here's a short example:
// This is the Map we have created
Map<String, String> eventData = new HashMap<>();
eventData.put("Event", "Data")
// We wrap that map in a SelfDescribingJson before sending it
SelfDescribingJson json = new SelfDescribingJson("iglu:com.acme/example/jsonschema/1-0-0", eventData);
Logging​
Logging in the Tracker is done using SLF4J. The majority of the logging set as DEBUG so it will not overly populate your own logging.
Since Java tracker v0.11, user-supplied values are only logged at DEBUG level.