Just Logger

Simple Java only logger without reflection or other magic

Motivation

• Logger with lazy messages
• Logger without reflections
• Logger which can run natively (GraalVM)
• Logger which is customizable
• Logger without huge dependency tree
• Logger simple to use (Always hard to find out how to set up SLF4J - afterwards it's awesome)

Function

Config -> Logger (LogLevel) -> Formatter (LogLevel) -> Writer

Usage

• Default

import berlin.yuna.justlog.logger.Logger;

public class UsageTest {

    private static final Logger logger = Logger.defaultLogger();

    public void log() {
        logger.warn(() -> "message", () -> new RuntimeException("exception"));
    }
}

Configuration

• Available LogLevel
• Configuration priorities [Environment Variables, Config Files, DSL]
• Configuration folders [classpath:resource, userDir, userDir:config]
• Configuration files [application.properties, logger.properties]
• Configuration values are [case insensitive]
  • Every config without logger. prefix will be ignored
• Example config

#Default logger config
logger.file=/user/home/service/config/custom.properties
logger.level=INFO
logger.threads=2
logger.writer.encoding=UTF8
logger.SimpleWriter.buffer-size=10
logger.pattern="[%p{l=10}] [%l{l=5}] [%d{p=HH:mm:ss.SSS}] [%c{l=10}] [%T{l=10,i=0}:%M:%L] %m%n%e{p=berlin,yuna}"
#Default logger config - the keyword root is optional and has no meaning
logger.root.file=/user/home/service/config/custom.properties
#Logger specific config
logger.myLoggerName.file=/user/home/service/config/custom.properties
logger.myLoggerClass.level=ERROR
logger.myLoggerClass.myFormatter.pattern="[[%d{p=HH:mm:ss.SSS}] [%c{l=10}] %m%n%e"

Pattern & Placeholder

• The log pattern defines the format of the log message by using placeholders
  • Placeholders are a simple chars with % as prefix
  • Placeholders are named provicers in code
  • It is also possible to create custom providers, see examples of DefaultProviders
• All default Providers:

Char	Accepts	Name	Description
a	l	IP Address	First IP Address of the current host
c	l	logger name	logger name
d	l, z	DateTime	date time using DateTimeFormatter
e	p	Exception	exception
h	l	Hostname	Hostname
l	l	Log Level	log level for that message
m	-	Message	actual message
n	-	New Line	new line
p	l	PID	process id of the current thread
T	l, i	Caller Class	Caller class name [slows the performance]
M	l, i	Caller Method	Caller Method [slows the performance]
L	l, i	Caller Line Number	Caller Line Number [slows the performance]

• Every Provider accepts , separated parameters within brackets {} like on default:

Char	Name	Examples
l	Length	%l{l=5} Loglevel length %c{l=10} LoggerName length
i	Index	%T{i=0} Caller class index number (0 = default)
p	Pattern	%d{p=HH:mm:ss.SSS} Date format %e{p=berlin;yuna} include only traces with packages in berlin and yuna
z	TimeZone	%d{z=UTC} Sets the time zone (UTC = default)

• DSL Config

public class UsageTest {

    private final Logger logger1;
    private final Logger logger2;

    public UsageTest {
        final HashMap<String, String> myOptionalConfig = new HashMap<>();

        logger1 = new DefaultLogger("LoggerName")
                .config(myOptionalConfig)
                .level(LogLevel.TRACE)
                .writer(new SimpleWriter())
                .formatter(new SimpleLogFormatter())
                .formatter().pattern("[%p{l=10}] [%l{l=5}] [%d{p=HH:mm:ss.SSS}] [%c{l=10}] [%T{l=10,i=0}:%M:%L] %m%n%e{p=berlin,yuna}").logger();

        logger2 = DefaultLogger.instance().config(myOptionalConfig).level(LogLevel.TRACE);
    }
}

TODOs

• Test the logger in a project
• String format message
• Config to enable automatically Json / Line logging
• FileWriter
• Accept Multiple Writer
• Split into Java version 8,11,17