Project log4j Debugging on --verbose

Internal

• projects
• clad
• Project Alternative log4j Configuration

Overview

A pattern that consists in dynamically turning on logging verbosity and routing all log4j logging information to stderr if -v or --verbose command line options are used. Projects that implement it are clad, gld, events-gc-parser, etc.

This pattern only applies to command line utilities, which are supposed to run in foreground and send their logging at stdout or stderr. For processes that run in background, use Project Alternative log4j Configuration. log4j debugging on --verbose and alternative log4j configuration can be combined, where --verbose flag applies until the configuration file is parsed and the new logging configuration is installed.

API

Use novaordis-utilities 4.2 or newer. novaordis-utilities 4.2.0 was the first release that contains StderrVerboseLogging.

For more details, see:

https://github.com/NovaOrdis/novaordis-utilities/blob/master/src/main/java/io/novaordis/utilities/logging/StderrVerboseLogging.java

StderrVerboseLogging comes with an init() static utility method that looks at the "verbose" system property and turns on stderr logging. The recommended usage pattern is:

import io.novaordis.utilities.logging.StderrVerboseLogging;

StderrVerboseLogging.init();

You should call StderrVerboseLogging.init() as early as possible after the JVM starts running. For suggestion on how to pass the logging verbosity option from the shell wrapper to the JVM, see Shell Wrapper Recommendations below.

If you want to enable logging manually in the program, use:

import io.novaordis.utilities.logging.StderrVerboseLogging;

...
if (verbose) {
    StderrVerboseLogging.enable();
}
...

Shell Wrapper Recommendations

The recommended way to pass the "verbose" information that was already identified by a bash wrapper to the JVM is to use:

-Dverbose=true

Typical bash wrapper code:

verbose=false
...
${verbose} && verbose_system_property="-Dverbose=true"

command="${java_bin} ... ${verbose_system_property} ${main_class}..."

application-shell-wrapper-template of bash-wrapper-functions implements this pattern.