Java apps

This guide covers packaging Java apps that run on a JRE or JDK pulled in via Zero Install.

Runtime feeds

https://apps.0install.net/java/jre.xml

The Java Runtime Environment. Minimum needed to run a Java app.

https://apps.0install.net/java/openjdk.xml

The OpenJDK Development Kit (compiler + tools). Use this as a build dependency.

https://apps.0install.net/java/jar-launcher.xml

A small helper that launches the Main-Class declared in a JAR manifest while preserving CLASSPATH. Use this when your app loads other JARs from CLASSPATH. java -jar ignores CLASSPATH, which prevents Zero Install from injecting library JARs.

Versions match the JRE/JDK feature release (1.8, 11, 17, 21, ...).

Running a self-contained JAR

If your JAR has a Main-Class and bundles all dependencies, the simplest feed template is:

<?xml version="1.0"?>
<interface xmlns="http://zero-install.sourceforge.net/2004/injector/interface">
  <name>MyApp</name>
  <summary>does something useful</summary>
  <homepage>https://example.com/myapp</homepage>

  <feed-for interface="https://example.com/myapp.xml"/>

  <group license="Apache-2.0">
    <command name="run" path="MyApp.jar">
      <runner interface="https://apps.0install.net/java/jre.xml" version="17..">
        <arg>-jar</arg>
      </runner>
    </command>

    <implementation version="{version}" released="{released}" stability="stable">
      <manifest-digest/>
      <file href="https://example.com/downloads/myapp-{version}.jar" dest="MyApp.jar"/>
    </implementation>
  </group>
</interface>

<file> (instead of <archive>) downloads a single JAR straight into the implementation directory. The runner invokes java -jar /path/to/MyApp.jar.

Apps with library JAR dependencies

Attention

When your app needs other JARs that are themselves Zero Install feeds, java -jar won't work, since it ignores CLASSPATH. Use JAR Launcher instead:

<command name="run">
  <environment name="CLASSPATH" insert="MyApp.jar"/>
  <runner interface="https://apps.0install.net/java/jar-launcher.xml" version="17.."/>
</command>

<requires interface="https://example.com/somelibrary.xml">
  <environment name="CLASSPATH" insert="somelibrary.jar"/>
</requires>

JAR Launcher reads the Main-Class attribute from the first JAR on CLASSPATH and invokes it normally, so any library JARs added via <environment name="CLASSPATH"> bindings are visible.

Distributing a folder of JARs

Some Java apps ship as a directory tree (an app/ folder, an lib/*.jar folder, optional native libraries). Treat them like any other binary archive:

<group license="MIT">
  <command name="run">
    <environment name="CLASSPATH" insert="lib/myapp.jar"/>
    <environment name="CLASSPATH" insert="lib" mode="append"/>
    <runner interface="https://apps.0install.net/java/jar-launcher.xml"/>
  </command>

  <implementation version="{version}" released="{released}" stability="stable">
    <manifest-digest/>
    <archive extract="myapp-{version}" href="https://example.com/downloads/myapp-{version}.tar.gz"/>
  </implementation>
</group>

If the app needs native libraries (JNI), add an <environment name="LD_LIBRARY_PATH" insert="lib"/> (or PATH on Windows, DYLD_LIBRARY_PATH on macOS) so the JVM can find them.

If the libraries differ per platform, follow the cross-platform recipe and ship one implementation per arch.