Dryuf OneJarLoader

ClassLoader which loads jar files from top level jar and adds them as dependencies - it allows distributing java application as single jar.

Release

<dependency>
	<groupId>net.dryuf</groupId>
	<artifactId>dryuf-onejarloader</artifactId>
	<version>1.0.2</version>
</dependency>

Usage

Create a main() function wrapper which initializes OneJarLoader ClassLoader and executes the true main() class:

public class JarMyApplication
{
        public static void main(String[] args)
        {
                OneJarLoader cl = new OneJarLoader();
                cl.invokeMain(JarMyApplication.class.getName() + ".MyApplication", args);
        }
}

Build a single jar with main class JarMyApplication, for example using maven-assembly-plugin:

			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-assembly-plugin</artifactId>
				<version>${maven-assembly-plugin.version}</version>
				<executions>
					<execution>
						<id>uber</id>
						<phase>package</phase>
						<goals>
							<goal>single</goal>
						</goals>
						<configuration>
							<archive>
								<manifest>
									<addClasspath>true</addClasspath>
									<mainClass>myproject.JarMyApplication</mainClass>
								</manifest>
							</archive>
							<finalName>${project.name}</finalName>
							<appendAssemblyId>false</appendAssemblyId>
							<descriptors>
								<descriptor>src/main/assembly/uber.xml</descriptor>
							</descriptors>
						</configuration>
					</execution>
				</executions>
			</plugin>

src/main/assembly/uber.xml example:

<assembly
	xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.3"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.3 http://maven.apache.org/xsd/assembly-1.1.3.xsd">
	<id>uber</id>
	<formats>
		<format>jar</format>
	</formats>
	<includeBaseDirectory>false</includeBaseDirectory>
	<dependencySets>
		<dependencySet>
			<outputDirectory>/</outputDirectory>
			<useProjectArtifact>true</useProjectArtifact>
			<unpack>false</unpack>
			<scope>runtime</scope>
			<excludes>
				<exclude>net.dryuf:dryuf-onejarloader</exclude>
			</excludes>
		</dependencySet>
		<dependencySet>
			<outputDirectory>/</outputDirectory>
			<useProjectArtifact>true</useProjectArtifact>
			<unpack>true</unpack>
			<scope>runtime</scope>
			<includes>
				<include>net.dryuf:dryuf-onejarloader</include>
			</includes>
		</dependencySet>
	</dependencySets>
	<fileSets>
		<fileSet>
			<directory>${project.build.directory}/classes/</directory>
			<outputDirectory>/</outputDirectory>
			<includes>
				<include>myproject/JarMyApplication.class</include>
			</includes>
			<useDefaultExcludes>true</useDefaultExcludes>
		</fileSet>
	</fileSets>
</assembly>

Additionally, you can add dryuf-executable-jar-maven-plugin to pom.xml to prepend #!/usr/bin/env -S java -jar to built executable:

			<plugin>
				<groupId>net.dryuf.maven.plugin</groupId>
				<artifactId>dryuf-executable-jar-maven-plugin</artifactId>
                <version>${dryuf-executable-jar-maven-plugin.version}</version>
				<executions>
					<execution>
						<phase>package</phase>
						<goals>
							<goal>create-executable</goal>
						</goals>
						<configuration>
							<vmParams>-Xmx256m</vmParams>
							<sort>true</sort>
							<resourceConfigs>
								<resourceConfig>
									<pattern>glob:**</pattern>
									<type>dir</type>
									<remove>true</remove>
								</resourceConfig>
								<resourceConfig>
									<pattern>glob:*.jar</pattern>
									<minimalCompress>100</minimalCompress>
								</resourceConfig>
							</resourceConfigs>
							<input>${project.build.directory}/${project.name}.jar</input>
						</configuration>
					</execution>
				</executions>
			</plugin>

You can then distribute and execute the command simply by target/myproject (or myproject if in PATH).

Features

The following is supported:

1. Loading classes.
2. Loading resources.
3. Loading native libraries from <os>/<arch>/the-lib.ext or the-lib.ext
4. Nesting JAR files indefinitely.

Performance

Extracting JAR files at the beginning runs in parallel, so more CPUs can bring benefit.

Test on 67 MB application on 4-core (8 hyperthreads) Intel 1185G7 or Graviton-3 showed 90-110 ms for the initialization.

Examples

Examples can be found in examples directory.

License

The code is released under version 2.0 of the Apache License.

Authors

Zbynek Vyskovsky - kvr000@gmail.com and https://github.com/kvr000/ and https://github.com/dryuf/ and https://www.linkedin.com/in/zbynek-vyskovsky/ .

Originally inspired by JarClassLoader but completely rewritten with Java 8 features and improved performance in mind.