Better Maven multithreaded build logging support

• Routes all (most) log messages to SLF4J.
• Uses SLF4J Mapped Diagnostic Context (or "MDC" for short) to identify per-project log messages.
• Provides a number of Maven-specific Logback extensions:
  • ProjectBuildLogAppender appender to write per-project log messages to ${project.build.directory}/build.log log files.
  • ProjectConsoleAppender appender to display per-project log messages as continuous block at the end of individual project build.
  • ProjectBuildLogFilter filter to allow/deny per-project build log messages.
  • BuildRollingPolicy rolloing policy to rotate log files at the begenning of a build.
  • ConsoleAppender console appender replacement for better console logging performance.

Build and installation

To build logging extensions and maven distribution

mvn clean integration-test -Pmaven-distro

Maven distribution with concurrent logging is created under target/ folder as maven-distro-${mavenVersion}-${project.version} archive.

Usage

Default Logback logging configuration included with the Maven distribution matches standard Maven (as of version 3.3.9).

A number of additional example Logback configuration files is included with the distribution to demostrate more advanced logging features.

-Dmaven.logging=<classifier> command line parameter allows switch between available configuration. For example, the following command selects M2_HOME/conf/logging/logback-dev.xml Logback configuration file:

mvn package -Dmaven.logging=dev

Provided example Logback configuration files

ci example logs all build log messages to the console. All build log messages are timestamped and include project artifactId and thread name. Use ci logging configuration classifier to enable this configuration, for example mvn package -Dmaven.logging=ci.

dev example provides more elaborate logging scheme useful when running and/or troubleshooting large multi-module builds on a developer workstation. Build console log only includes overall build log messages with INFO or higher severity, which provides build progress and particularly useful with Takari Smart Builder multi-threaded build scheduler. To facilitate build troublshooting, all build log messages are written to build.log file located in the current directory and project-specific build log messages are written to build.log files located in ${project.build.directory}. Messages written to build.log files honour -X/--debug Maven command line parameter. All messages are timestamped and can be correlated between console, build.log files and external log files. Additionally, messages written to overall build.log file are stamped with project artiactId and thread of the message. Note messages written to project-specific build.log files are buffered during execution of clean lifecycle and are lost of jvm crashes or killed before default lifecycle execution starts for the project. Use dev logging configuration classifier to enable this configuration, for example mvn package -Dmaven.logging=dev.

byproject logging configuration example groups together log messages from individual reactor build projects and prints them to the console after projects builds finish. Project messages never interleave with messages from other projects or overall build log messages. This is useful when multiple projects are built concurrently and default Maven logging makes it difficult to correlated log messages to individual projects. The downside of this configuration, build may appear "stuck" due to message buffering. Buffered messages will be lost in the build jvm crashes or killed by the user. Use byproject logging configuration classifier to enable this configuration, for example mvn package -Dmaven.logging=byproject.

Under the hood

System out/err

Uses custom PrintStream to capture System out/err messages and route them to SLF4J logger. Same idea as sysout-over-slf4j but independent Maven-compatible implementation.

System out/err capture is enabled during batch builds only (-B/--batch mvn invocation parameter) because it interferes with user console interaction, like, for example, release plugin asking for release version.

Implementation uses slow caller stack walkback to determine if System out/err messages should be captured or passed through to the console. This can result in poor console logging performance. To avoid the problem, use either io.takari.maven.logback.ConsoleAppender console appender (fully compatible with standard Logback console appender) or io.takari.maven.logback.ProjectConsoleAppender (groups console messages by project).

java.util.logging (or "JUL" for short)

Uses jul-to-slf4j to capture JUL log messages and route them to SLF4J.

log4j 1.x and commons-logging

Uses log4j-over-slf4j and jcl-over-slf4j to capture and route log4j and commons logging log messages to SLF4j. Replaces plugin dependencies with corresponding bridge libraries as part of plugin classrealm setup.

Known issues

• none at this point