Java .gitignore Template Explained

Java.gitignore is a short template of about 13 lines that deals only with compilation output and files left by the JVM. It does not include Maven's target/ or Gradle's build/, so real projects usually combine it with the Maven or Gradle template and an IDE template.

The rule to watch most closely is *.jar. It is meant to keep distribution archives out of the repository, but it also ignores build-tool wrapper jars, so you need to pay attention to the order of the combination.

Rules explained

Pattern	What it ignores and why
*.class	Compilation outputBytecode that javac produces from source. It can be rebuilt at any time from the source, and its contents vary by compiler version.
*.jar*.war*.nar*.ear*.zip*.tar.gz*.rar	Package archivesDistribution files and compressed archives produced by builds. The goal is to fetch dependency jars from a repository such as Maven Central instead of the old practice of putting them directly in the repository.
hs_err_pid*replay_pid*	JVM crash logshs_err_pid<number>.log, which the JVM leaves in the working directory when it crashes, and replay_pid files for reproducing JIT compiler issues. They are one-off debugging files.
*.log	LogsApplication run logs. Committing log files creates changes on every run and can leak operational information.
*.ctxt.mtj.tmp/	BlueJ and J2MEContext files from the educational IDE BlueJ and the temporary folder of Mobile Tools for Java (J2ME). They have no effect if you do not use those tools.

Practical notes

• *.jar also ignores the Gradle wrapper's gradle/wrapper/gradle-wrapper.jar. The Gradle template's !gradle-wrapper.jar solves this, but because git follows the last matching rule, you must select them so that Gradle comes after Java.
• Build folders (target/, build/) are not in this template. Add the Maven or Gradle template.
• IDE files such as IntelliJ's .idea/ and Eclipse's .project and .classpath are handled by the JetBrains and Eclipse templates.
• If you really must keep library jars in the repository, re-include only a specific path, such as !libs/*.jar.

Original template

# Compiled class file*.class# Log file*.log# BlueJ files*.ctxt# Mobile Tools for Java (J2ME).mtj.tmp/# Package Files #*.jar*.war*.nar*.ear*.zip*.tar.gz*.rar# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xmlhs_err_pid*replay_pid*

Often used together

More template explanations