e-help

JDK Bin Tools Reference

A quick reference for every tool in $JAVA_HOME/bin — what it does and a simple example.

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All Available Commands

Tool	Category	What it does
jar	Package	Create / manage JAR archives
jarsigner	Security	Sign or verify JARs
java	Run	Run a class, JAR, or source file
javac	Compile	Compile .java → .class
javadoc	Compile	Generate HTML docs from comments
javap	Compile / Debug	Disassemble .class files
jcmd	Monitor	All-in-one live JVM diagnostics
jconsole	Monitor	GUI JMX monitor
jdb	Debug	Command-line debugger
jdeprscan	Compile	Find deprecated API usage in a JAR
jdeps	Compile	Show module/package dependencies
jfr	Monitor	Production profiler (Flight Recorder)
jhsdb	Debug	Post-mortem crash analysis
jimage	Package	Inspect JDK module images
jinfo	Debug	Show JVM flags of a running process
jlink	Package	Build a custom minimal JRE
jmap	Debug	Heap dump — diagnose memory leaks
jmod	Package	Create JMOD module packages
jnativescan	Native	Scan for restricted native method usage
jpackage	Package	Build native OS installers
jps	Monitor	List running Java processes
jrunscript	Run	Run scripts from CLI
jshell	Run	Interactive Java REPL
jstack	Debug	Thread dump — diagnose hangs/deadlocks
jstat	Monitor	Stream GC / class loading stats
jstatd	Monitor	Daemon for remote monitoring
jwebserver	Run	One-command static file server
keytool	Security	Manage keystores and certificates
native-image	Native (GraalVM)	Compile Java to native binary
native-image-configure	Native (GraalVM)	Generate reflection config for native-image
native-image-inspect	Native (GraalVM)	Inspect native binary contents
rmiregistry	Legacy	RMI naming registry
serialver	Legacy	Get serialVersionUID for a class

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Examples

jar — Create and manage JARs

jar --create --file app.jar --main-class Hello Hello.class   # create a JAR
java -jar app.jar                                             # run it
jar --list --file app.jar                                     # list contents
jar --extract --file app.jar                                  # unzip
jar --update --file app.jar Hello.class                       # update a file inside

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jarsigner — Sign or verify a JAR

# sign
jarsigner -keystore keystore.jks app.jar mykey

# verify
jarsigner -verify -verbose app.jar

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java — Run your application

java Hello                    # run a compiled class
java -jar myapp.jar           # run a JAR
java Hello.java               # run a single file directly (Java 11+)
java -Xmx512m -jar myapp.jar  # run with 512 MB heap limit

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javac — Compile source files

// Hello.java
public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

javac Hello.java              # produces Hello.class
javac -d out/ src/**/*.java   # compile whole folder into out/

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javadoc — Generate HTML API docs

/**
 * Simple calculator utility.
 * @author Dev
 */
public class Calculator {
    /** Adds two numbers. @param a first @param b second @return sum */
    public int add(int a, int b) { return a + b; }
}

javadoc -d docs/ Calculator.java
# open docs/index.html in a browser

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javap — Disassemble .class files

javap Hello              # show public method signatures
javap -c Hello           # show bytecode instructions
javap -p -verbose Hello  # show everything including private members

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jcmd — Live JVM diagnostics

jcmd                          # list all running JVM processes
jcmd 12345 help               # list available commands for that process
jcmd 12345 Thread.print       # thread dump
jcmd 12345 GC.run             # force garbage collection
jcmd 12345 VM.flags           # print all JVM flags
jcmd 12345 GC.heap_info       # heap summary

Prefer jcmd over the older jmap/jstack on modern JDKs.

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jconsole — GUI JMX monitor

jconsole                      # open GUI, pick a local process
jconsole hostname:9999        # connect to a remote JVM

# Enable JMX on app startup for remote access
java -Dcom.sun.management.jmxremote \
     -Dcom.sun.management.jmxremote.port=9999 \
     -Dcom.sun.management.jmxremote.authenticate=false \
     -jar myapp.jar

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jdb — Command-line debugger

javac -g Hello.java    # compile with debug info first
jdb Hello

> stop in Hello.main   # set a breakpoint
> run                  # start execution
> next                 # step to next line
> print x              # inspect a variable
> cont                 # continue execution
> quit

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jdeprscan — Find deprecated API usage

jdeprscan --release 21 myapp.jar   # scan against Java 21 deprecations
jdeprscan --release 21 --list      # list all deprecated APIs in Java 21

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jdeps — Analyze dependencies

jdeps myapp.jar                      # show all dependencies
jdeps --jdk-internals myapp.jar      # find internal JDK API usage
jdeps --print-module-deps myapp.jar  # summarize by module

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jfr — Java Flight Recorder

# start recording on a running JVM
jfr start name=myrec filename=out.jfr jvm=12345

# stop and save
jfr stop name=myrec jvm=12345

# print summary from CLI
jfr print out.jfr

# or enable at JVM startup
java -XX:StartFlightRecording=filename=out.jfr,duration=60s -jar myapp.jar

Open out.jfr in JDK Mission Control for flame graphs and GC analysis.

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jhsdb — Post-mortem / crash debugger

jhsdb hsdb --pid 12345                                         # GUI — attach to live process
jhsdb jstack --pid 12345                                       # thread dump via jhsdb
jhsdb jstack --core core.1234 --exe $JAVA_HOME/bin/java        # analyze a core dump

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jimage — Inspect JDK module images

jimage list $JAVA_HOME/lib/modules                    # list all modules
jimage extract --dir ./out $JAVA_HOME/lib/modules     # extract to a folder
jimage info $JAVA_HOME/lib/modules                    # show image metadata

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jinfo — JVM flags and system properties

jinfo 12345                        # print all JVM info
jinfo -flag MaxHeapSize 12345      # check a specific flag
jinfo -sysprops 12345              # list all system properties

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jlink — Build a custom minimal JRE

jlink \
  --module-path $JAVA_HOME/jmods \
  --add-modules java.base,java.logging,java.sql \
  --compress 2 \
  --output my-runtime

my-runtime/bin/java -jar myapp.jar   # run with the custom JRE

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jmap — Heap dumps and memory maps

jmap -heap 12345                               # heap summary
jmap -dump:format=b,file=heap.hprof 12345      # full heap dump
jmap -histo 12345 | head -20                   # top memory consumers

Open heap.hprof in VisualVM or Eclipse MAT to find memory leaks.

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jmod — Create JMOD module packages

jmod create \
  --class-path mods/com.example \
  --main-class com.example.Main \
  com.example.jmod

jmod list com.example.jmod       # list contents
jmod describe com.example.jmod   # describe the module

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jnativescan — Scan for restricted native calls (Java 22+)

jnativescan --class-path myapp.jar

jnativescan --module-path mods/ --add-modules com.example

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jpackage — Build native installers

# macOS .dmg
jpackage --input lib/ --main-jar myapp.jar \
  --main-class com.example.Main --name MyApp --type dmg

# Windows .msi
jpackage --input lib/ --main-jar myapp.jar --name MyApp --type msi

# Linux .deb
jpackage --input lib/ --main-jar myapp.jar --name myapp --type deb

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jps — List running Java processes

jps          # pid + main class name
jps -v       # include JVM arguments
jps -l       # full main class name

Always run this first to get the PID before using jcmd, jstack, jmap, etc.

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jrunscript — Run scripts from CLI

jrunscript -e "print('hello')"   # one-liner
jrunscript myscript.js           # run a script file

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jshell — Interactive Java REPL

$ jshell
jshell> int x = 10;
jshell> System.out.println(x * x);    // 100
jshell> var list = List.of(1, 2, 3);
jshell> list.stream().map(n -> n * 2).toList()
jshell> /open utils.java              // load a file into the session
jshell> /exit

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jstack — Thread dump

jps                              # find the PID first
jstack 12345                     # print all thread traces
jstack 12345 > threads.txt       # save to file for analysis
jstack -l 12345                  # include lock info for deadlock detection

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jstat — Real-time JVM statistics

jstat -gc 12345 1000        # GC stats every 1 second
jstat -gcutil 12345 1000    # GC utilisation as percentages
jstat -class 12345          # class loading stats
jstat -compiler 12345       # JIT compiler activity

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jstatd — Remote monitoring daemon

# jstatd.policy
grant codebase "file:${java.home}/../lib/tools.jar" {
    permission java.security.AllPermission;
};

jstatd -J-Djava.security.policy=jstatd.policy   # start the daemon
jstat -gc //remotehost/12345 1000               # connect remotely

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jwebserver — Static HTTP file server (Java 18+)

jwebserver                          # serve current dir on port 8000
jwebserver -p 9090 -d ./public      # custom port and directory
jwebserver -b 0.0.0.0 -p 8080      # bind to all network interfaces

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keytool — Manage keystores and certificates

# generate a key pair (self-signed certificate)
keytool -genkeypair -alias mykey -keyalg RSA -keysize 2048 \
  -validity 365 -keystore keystore.jks

# list all entries in a keystore
keytool -list -keystore keystore.jks

# import a CA certificate
keytool -importcert -alias myca -file ca.crt -keystore truststore.jks

# export a certificate to a file
keytool -exportcert -alias mykey -file mycert.crt -keystore keystore.jks

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native-image — Compile Java to a native binary (GraalVM)

native-image -jar myapp.jar        # compile a JAR

./myapp                            # run — no JVM needed!

# with reflection configuration
native-image -H:ReflectionConfigurationFiles=reflect.json -jar myapp.jar

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native-image-configure — Generate reflection/JNI config (GraalVM)

# step 1: run your app with the tracing agent
java -agentlib:native-image-agent=config-output-dir=config/ -jar myapp.jar

# the agent creates these files in config/
#   reflect-config.json
#   jni-config.json
#   resource-config.json

# step 2: use the configs in the native-image build
native-image -H:ConfigurationFileDirectories=config/ -jar myapp.jar

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native-image-inspect — Inspect native binary contents (GraalVM)

native-image-inspect --list-classes ./myapp    # all included classes
native-image-inspect --list-methods ./myapp    # all included methods

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rmiregistry — RMI naming registry (legacy)

rmiregistry          # start on default port 1099
rmiregistry 2000     # start on a custom port

// register a remote object in code
Registry reg = LocateRegistry.getRegistry(1099);
reg.bind("MyService", myRemoteObject);

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serialver — Get serialVersionUID (legacy)

serialver com.example.MyModel
# output:
# com.example.MyModel: static final long serialVersionUID = -1234567890123456789L;

// paste the result into your class
public class MyModel implements Serializable {
    static final long serialVersionUID = -1234567890123456789L;
    // ...
}

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Prepared for the Java Community of Practice.