Replace hand-written SLF4J logger fields by Lombok @Slf4j #602

Proposal

Replace the hand-written logger fields, such as:

private static final Logger LOGGER = LoggerFactory.getLogger(ProcessorSimple.class.getSimpleName());

by Lombok's @Slf4j annotation. Lombok is already used across the project.

• @Slf4j generates the logger field with the SLF4J API.
• Logback stays the SLF4J implementation, as it is today. util.Log already uses Logback to change log levels.

This removes repeated code (25 declarations in src/main). It also avoids copy-and-paste mistakes, where the class name passed to getLogger() isn't the class that declares the field.

Points to decide

1. Field name. @Slf4j creates a field called log by default. Add lombok.log.fieldName = LOGGER to lombok.config, so existing code (LOGGER.warn(...)) doesn't change.
2. Logger name. Today loggers are named with getSimpleName() (for example ProcessorSimple). @Slf4j uses the full class name (org.cloudsimplus.resources.ProcessorSimple).
   • Log levels set with Log.setLevel(logger, level) keep working, since they get the logger object.
   • A logback.xml that sets levels by the short names would stop matching.
   • The current log pattern (%-5level %msg%n) doesn't print the logger name, so the output doesn't change.
   • Options:
     • accept the full names (the usual convention, and it allows per-package levels such as org.cloudsimplus.schedulers);
     • or use @Slf4j(topic = "ProcessorSimple"), which repeats the class name again.
3. Interfaces can't use @Slf4j. 13 public interfaces declare a public LOGGER constant, which their implementations use. They are Vm, Host, Datacenter, DatacenterBroker, VmAllocationPolicy, VmScheduler, CloudletScheduler, VmScaling, FileStorage, TraceReader, Heuristic, HeuristicSolution and VmCloner.
   • These constants are part of the public API. For example, the examples call Log.setLevel(DatacenterBroker.LOGGER, Level.ERROR), and some trace readers call broker.LOGGER.trace(...).
   • Options:
     • keep these constants as they are and use @Slf4j only in classes;
     • or move each logger to the main abstract class (for example DatacenterBrokerAbstract) with @Slf4j. That is a breaking change for user code that uses Vm.LOGGER and the other constants.
   • Removing the constants also changes which logger an implementation uses. Today VmSimple logs through Vm.LOGGER, so one Log.setLevel(Vm.LOGGER, …) call controls every VM class.

Tasks

• Decide points 1–3 above.
• Add lombok.log.fieldName = LOGGER to lombok.config, if that option is chosen.
• Replace the logger fields in classes by @Slf4j, and remove the unused Logger/LoggerFactory imports.
• Update logback.xml/logback-test.xml and the docs, if logger names change.
• Check the cloudsimplus-examples that call Log.setLevel(...) on these loggers.

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