Event Logger

Requirements

• Accept a message at one of several severity levels
• Write to more than one destination — console and file at minimum
• Drop events below a configured minimum level
• Let the destinations be configured without changing calling code
• Allow a destination to format its output differently from the others

Assumptions you may make

• Single process; concurrency is an extension, not a requirement
• You may assume a destination never fails

Things the brief expects to exist

Candidates, not a design. How they relate is yours to decide.

Logger

Accepts events and passes those above the threshold to its sinks

LogSink

Writes one formatted event somewhere

LogEvent

Carries the message, level and timestamp

LogLevel

Orders severities so a threshold comparison is possible

Formatter

Turns an event into the text a sink writes

What this exercise is teaching

• Separate deciding what to log from deciding where it goes
• Add a destination without editing the logger
• Recognise when a small interface is better than a large one

Once it works, make it survive these

• Add an asynchronous destination that batches writes
• Add a destination that only receives errors
• Make the logger safe to call from several threads