Java Cheatsheet - Java & JVM Command Reference

This reference is for developers writing Spring Boot/WAR apps or operating them in production: from compiling and packing with javac/java/jar, one-command builds with Maven/Gradle, heap sizing with -Xms/-Xmx, G1 GC and GC logging, to grabbing threads and heap with jstack/jmap/jstat when the service stalls. Unlike a generic command list, it is organized around building the service, running it stably, tuning it faster, and debugging its failures. After reading you should be able to complete a build → deploy → GC tune → deadlock hunt cycle on your own.

Languages·34 commands·Last updated 2026-07-21

Compile & Run 6

javac Main.java

Compile a single Java file

java -cp .:lib.jar Main

Run with classpath (Linux/Mac)

java -cp ".;lib.jar" Main

Run with classpath (Windows)

jar cvf app.jar *.class

Package classes into a jar

jar tf app.jar

List jar contents

jar xf app.jar

Extract a jar

Maven Commands 8

mvn clean

Clean the target directory

mvn compile

Compile main sources

mvn test

Run unit tests

mvn package

Package (jar/war)

mvn install

Install to local repo

mvn dependency:tree

Show the dependency tree

mvn -U clean package

Force snapshot update and package

mvn spring-boot:run

Run a Spring Boot project

Gradle Commands 6

./gradlew build

Build the project

./gradlew clean

Clean the build dir

./gradlew test

Run tests

./gradlew bootRun

Run Spring Boot project

./gradlew dependencies

Show dependencies

./gradlew tasks

List all available tasks

JVM Flags & Tuning 6

java -Xms512m -Xmx2g -jar app.jar

Set heap min 512M / max 2G

java -XX:+UseG1GC -jar app.jar

Use the G1 garbage collector

java -XX:+PrintGCDetails -Xloggc:gc.log

Log GC details to a file

java -XX:+HeapDumpOnOutOfMemoryError

Dump heap on OutOfMemoryError

java -XX:HeapDumpPath=/tmp/dump.hprof

Set the heap dump path

java -verbose:gc

Print brief GC info

JVM Troubleshooting 8

jps -l

List all Java processes

jstack <pid>

Dump thread stack (find deadlocks)

jmap -heap <pid>

Inspect heap usage

jmap -dump:format=b,file=dump.hprof <pid>

Dump a heap snapshot

jstat -gcutil <pid> 1000

Print GC stats every second

jinfo <pid>

View JVM flags

jconsole

Graphical monitoring tool

visualvm

Visual JVM profiler

Tips

With jstack, look for "Found one Java-level deadlock" to spot deadlocks.
Heap dump files can be huge - check disk space in production first.
G1 GC suits large heaps (>6G); Parallel GC gives higher throughput on small heaps.

Official References

Each command links to its official documentation below, so you can verify the latest usage and read deeper.

Java Docs

Maintained by LaoHand

Publicly updated on Jul 21, 2026, continuously proofread against official docs.

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