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Launch4j does not normally place a complete Java runtime inside the .exe. It creates a native Windows launcher. To ship an application that works without a separate Java installation, distribute a complete JRE or runtime image beside the executable and configure Launch4j to search that directory first.
A typical release looks like this:
MyApp/
├─ MyApp.exe
├─ lib/
│ ├─ dependency-one.jar
│ └─ dependency-two.jar
└─ jre/
├─ bin/
│ └─ javaw.exe
├─ conf/
└─ lib/The Bundled JRE path setting does not download or copy Java. It tells the generated launcher where the runtime supplied by you is located.
What Launch4j actually bundles
There are three separate ideas:
- Launcher wrapping: Launch4j generates
MyApp.exe, which starts Java with your application settings. - Bundled runtime: Your release archive contains a JRE or modular runtime image.
- Runtime embedded in the executable: The runtime is merged into the binary itself. This is not Launch4j’s normal operating model.
Launch4j 3.50 documents a configured path such as jre and searches configured paths before the Windows registry. A valid runtime must nevertheless exist at that path. See the Launch4j documentation.
Prerequisites and runtime choices
- A working application with a known fully qualified main class.
- A built JAR or deliberately configured classpath.
- Launch4j 3.50, or the version you are using.
- A Windows-compatible runtime matching your application’s Java version and architecture.
- Any native libraries, JavaFX components, or external JAR dependencies your application needs.
- A clean Windows test machine or virtual machine without Java installed.
Choose a runtime source
For a simple first deployment, obtain a vendor runtime such as Eclipse Temurin. Eclipse directs users to its Temurin project downloads and the Adoptium API. Do not hard-code an update number in a general build guide; Java security updates change frequently, and you must review the selected vendor’s current redistribution terms.
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For Java 9 and later, a “JRE” may instead be a custom runtime image created with jlink. A full vendor runtime is easier to assemble; a custom image can reduce included modules but requires more testing.
Prepare the release directory
The runtime directory must be beside the final executable, not merely beside your project file. Preserve the complete internal layout; copying only java.exe or javaw.exe is insufficient.
release/
├─ MyApp.exe
├─ MyApp.jar
├─ lib/
│ ├─ dependency-one.jar
│ └─ dependency-two.jar
└─ jre/
├─ bin/
│ └─ javaw.exe
├─ conf/
└─ lib/The JAR is shown separately because the exact Launch4j wrapping mode and dependency arrangement determine whether it remains in the release. If your configuration expects external libraries, keep those libraries in the configured classpath.
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Configure Launch4j
You can use launch4j.exe without arguments for the GUI, but save the resulting XML in source control and build with launch4jc.exe config.xml for repeatable releases. Launch4j’s paths may be absolute or relative to the configuration file when building; the bundled runtime path is resolved relative to the executable when the application starts.
Representative XML
<?xml version="1.0" encoding="UTF-8"?>
<launch4jConfig>
<headerType>gui</headerType>
<outfile>releaseMyApp.exe</outfile>
<jar>buildMyApp.jar</jar>
<errTitle>MyApp</errTitle>
<chdir>.</chdir>
<classPath>
<mainClass>com.example.Main</mainClass>
</classPath>
<jre>
<path>jre</path>
<requires64Bit>true</requires64Bit>
<minVersion>17</minVersion>
</jre>
</launch4jConfig>Change gui to console for a command-line program. The mainClass must match the actual entry point. The jar identifies the application JAR used by the wrapper; it does not by itself copy a runtime into the output directory.
The bundled path, version, and architecture settings
The central setting is:
<jre>
<path>jre</path>
</jre>The directory name is not mandatory, but the value must exactly match it. For a 64-bit-only application or native dependency, use <requires64Bit>true</requires64Bit>. This selects a 64-bit runtime; it cannot make a 32-bit native library compatible.
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For Java 9 and later, use a version such as <minVersion>17</minVersion>. Java 8-style versions use forms such as 1.8.0 or 1.8.0_121. Launch4j documents the Java 9-plus format as xxx[.xxx[.xxx]]; an underscore update suffix is not valid in that format. Use maxVersion when you need an upper bound as well.
In the GUI, these values correspond to the Basic tab’s output and JAR fields, the classpath/main-class controls, and the JRE tab’s bundled path, version, and bitness controls. Labels can vary by release, so treat the saved XML as authoritative and avoid obsolete fields such as bundledJre64Bit, runtimeBits, or bundledJreAsFallback.
Build a reproducible release
One Windows command sequence is:
rmdir /S /Q release 2>NUL
mkdir release
mkdir releasejre
copy buildMyApp.jar releaseMyApp.jar
xcopy /E /I /Y C:runtimestemurin-17-jre releasejre
launch4jc.exe config.xmlAdjust the runtime source and JAR locations to your build. If the runtime archive extracts to an extra top-level directory, flatten the copy so that releasejrebinjavaw.exe exists directly. Ship a manifest or archive containing the executable, runtime, libraries, README, and applicable license notices. Record the exact Java feature line and runtime update used for each release.
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Creating a custom runtime with jlink
A Java 9-or-newer application can use a modular runtime image instead of a vendor directory:
jlink ^
--add-modules java.base,java.desktop,java.logging ^
--strip-debug ^
--no-man-pages ^
--no-header-files ^
--compress=2 ^
--output releasejreThe module list is application-specific. JavaFX, JDBC drivers, TLS providers, reflection-heavy frameworks, service loading, and native libraries may require additional modules or files. A reliable process is to run first with a full JDK, identify missing modules, rebuild the image, and test it on a clean machine. Never assume the example list is universal.
Verify that the bundled runtime is really used
- Copy the complete release to a Windows VM or PC with no Java installed.
- Repeat on a machine with an incompatible Java version and, where relevant, only 32-bit Java installed.
- Run the executable from a path containing spaces, then move the complete release elsewhere and run it again.
- Log the runtime selected by the process:
System.getProperty("java.version");
System.getProperty("java.home");
System.getProperty("os.arch");A successful launch on your development computer is not proof that the bundled runtime was selected: JAVA_HOME, PATH, registry entries, or an otherwise compatible system Java can mask a broken release.
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Troubleshoot common failures
| Symptom | Likely cause | Fix |
|---|---|---|
| Java runtime not found | Missing or incorrectly nested runtime; wrong relative path; executable moved alone | Place the complete runtime at releasejre, beside the executable, and rebuild or copy the whole release. |
| Runs only on the developer PC | System Java is masking the bundle | Test on a clean VM and inspect java.home and java.version. |
| Version error | Runtime is below minVersion or version syntax is wrong |
Use Java 8 syntax for Java 8 and a form such as 17 for Java 9-plus. |
| 64-bit error | Runtime or native dependency architecture mismatch | Use matching binaries and set requires64Bit when required. |
ClassNotFoundException or NoClassDefFoundError |
Application dependency is absent or not on the classpath | Correct the Launch4j classpath and ship the required lib files. |
FindException or module errors |
jlink image omitted a required module |
Add the module, rebuild the image, and retest. |
| JavaFX fails to start | JavaFX modules or platform-native files are absent | Include compatible JavaFX runtime components and their native libraries. |
Working-directory and installation permissions
<chdir>.</chdir> tells Launch4j to change to the executable directory, avoiding assumptions about how a shortcut or file association sets the current directory. Do not store mutable user data beside an executable installed under protected locations such as Program Files; use an appropriate per-user data directory instead.
When jpackage is a better fit
Launch4j is a launcher wrapper. It does not by itself provide an installer, shortcuts, uninstall support, upgrades, registry integration, or signing. jpackage creates application images containing application files and a runtime image, and can produce Windows exe and msi packages. A basic image command is:
jpackage ^
--type app-image ^
--name MyApp ^
--input input ^
--main-jar MyApp.jar ^
--main-class com.example.MainUnless --runtime-image is supplied, jpackage creates a runtime through jlink. Windows packages must be built on Windows; Oracle documents no cross-platform build support. Existing Launch4j XML workflows may therefore be simpler to retain, while new projects needing native installation should evaluate jpackage.
Quick Recap
Release maintenance
- Track the Java feature line and exact runtime update used.
- Apply security updates, rebuild, and retest the runtime.
- Review the selected vendor’s current license and redistribution terms.
- Sign the executable and installer as a separate release step; bundling Java does not remove SmartScreen or antivirus warnings.
- Keep the runtime, application, native libraries, and architecture aligned in every release.
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