Logging
The ringo/logging module provides a rich and fine-grained logging API. It uses Simple Logging Facade for Java (SLF4J) as abstraction layer for various Java logging frameworks, e.g. java.util.logging, log4j and logback, allowing the end user to plug in the desired logging framework at deployment time.
By default, RingoJS comes with and uses Apache log4j. The default log4j configuration for RingoJS is in modules/config/log4j.properties. Web apps can override this by providing their own configuration in config/log4j.properties. Using this file, setting log levels for individual loggers/modules is straightforward (e.g. uncommenting log4j.category.ringo.webapp = DEBUG enables debug log messages for ringo/webapp module). Note that as of RingoJS 0.5 you have to restart ringo for changes in log4j configuration to take effect.
All logger methods take a variable number of arguments. If the first argument passed to any of the logging methods is a string containing any number of curly bracket pairs ({}), the logger will interpret it as format string and use any following arguments to replace the curly bracket pairs. If an argument is an Error or Java Exception object, the logger will render a stack trace for it and append it to the log message. If the first string does not contain {} placeholders, or the number of arguments exceeds the number of placeholders, arguments are simply concatenated.
var log = require("ringo/logging").getLogger(module.id);
log.info("Hello {}", "world", 1, 2, 3);
// 0 [main] INFO <shell> - Hello world 1 2 3Additionally, one can intercept log messages which is also how responselog JSGI middleware works (for a demo see, e.g.: http://ringojs.org/demo/logging?info=1).
Consequently, configuring log levels for the to be used logging implementation (e.g. config/log4j.properties) will similarly work for responselog as well.
Another detail worth mentioning here's that timestamps showing up in responselog are relative to respective begin of requests.
