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A custom classloader to be used from maven generated artifacts to allow executable jars and custom exclusion of some libraries at runtime (eg. swt libraries). Based on code and packing strategy from eclipse.

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eclipse-jarinjarloader

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Desciption

A custom class loader based on eclipse code to allow executable jars and custom exclusion of some libraries at runtime.

Features

How to use it

See the eclipse-jarinjarloader-swt-sample/pom.xml to see how to configure this. You will just need to change the properties for main class and the version of the jarinjarloader.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<prerequisites>
		<maven>3.0.4</maven>
	</prerequisites>
	<parent>
		<groupId>org.raisercostin</groupId>
		<artifactId>eclipse-jarinjarloader-parent</artifactId>
		<version>1.3-SNAPSHOT</version>
	</parent>
	<artifactId>eclipse-jarinjarloader-swt-sample</artifactId>
	<packaging>jar</packaging>

	<properties>
		<swt.version>4.3</swt.version>
		<main.class>org.raisercostin.jarinjarloader.sample.JarInJarSwtMain</main.class>
		<jarinjarloader.version>${project.version}</jarinjarloader.version>
	</properties>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-dependency-plugin</artifactId>
				<executions>
					<execution>
						<id>copy-dependencies</id>
						<phase>prepare-package</phase>
						<goals>
							<goal>copy-dependencies</goal>
						</goals>
						<configuration>
							<outputDirectory>${project.build.directory}/classes/lib</outputDirectory>
							<overWriteReleases>false</overWriteReleases>
							<overWriteSnapshots>false</overWriteSnapshots>
							<overWriteIfNewer>true</overWriteIfNewer>
							<includeScope>runtime</includeScope>
						</configuration>
					</execution>
					<execution>
						<id>unpack</id>
						<phase>prepare-package</phase>
						<goals>
							<goal>unpack</goal>
						</goals>
						<configuration>
							<artifactItems>
								<artifactItem>
									<groupId>org.raisercostin</groupId>
									<artifactId>eclipse-jarinjarloader</artifactId>
									<version>${jarinjarloader.version}</version>
									<type>jar</type>
									<overWrite>false</overWrite>
									<outputDirectory>${project.build.directory}/classes</outputDirectory>
								</artifactItem>
							</artifactItems>
						</configuration>
					</execution>
				</executions>
			</plugin>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-jar-plugin</artifactId>
				<configuration>
					<archive>
						<manifest>
							<addClasspath>true</addClasspath>
							<classpathPrefix>lib/</classpathPrefix>
							<mainClass>org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader</mainClass>
						</manifest>
						<manifestEntries>
							<Class-Path>./</Class-Path>
							<Rsrc-Main-Class>${main.class}</Rsrc-Main-Class>
							<Class-Path-Filter-Match-On-osName-linux---osArch-i386>org.eclipse.swt.gtk.linux.x86</Class-Path-Filter-Match-On-osName-linux---osArch-i386>
							<Class-Path-Filter-Match-On-osName-linux---osArch-x86-64>org.eclipse.swt.gtk.linux.x86_64</Class-Path-Filter-Match-On-osName-linux---osArch-x86-64>
							<Class-Path-Filter-Match-On-osName-linux---osArch-amd64>org.eclipse.swt.gtk.linux.x86_64</Class-Path-Filter-Match-On-osName-linux---osArch-amd64>
							<Class-Path-Filter-Match-On-osName-windows-7---osArch-x86>org.eclipse.swt.win32.win32.x86</Class-Path-Filter-Match-On-osName-windows-7---osArch-x86>
							<Class-Path-Filter-Match-On-osName-windows---osArch-x86>org.eclipse.swt.win32.win32.x86</Class-Path-Filter-Match-On-osName-windows---osArch-x86>
							<Class-Path-Filter-Match-On-osName-windows---osArch-x86-64>org.eclipse.swt.win32.win32.x86_64</Class-Path-Filter-Match-On-osName-windows---osArch-x86-64>
							<Class-Path-Filter-Match-On-osName-windows---osArch-amd64>org.eclipse.swt.win32.win32.x86_64</Class-Path-Filter-Match-On-osName-windows---osArch-amd64>
							<Class-Path-Filter-Match-On-osName-mac-os-x---osArch-i386>org.eclipse.swt.cocoa.macosx</Class-Path-Filter-Match-On-osName-mac-os-x---osArch-i386>
							<Class-Path-Filter-Match-On-osName-mac-os-x---osArch-x86-64>org.eclipse.swt.cocoa.macosx.x86_64</Class-Path-Filter-Match-On-osName-mac-os-x---osArch-x86-64>
						</manifestEntries>
					</archive>
				</configuration>
			</plugin>
		</plugins>
	</build>
	<dependencies>
		<!--dependency needed to compile on the current dev environment-->
		<dependency>
			<groupId>org.eclipse.swt</groupId>
			<artifactId>${swt.artifactId}</artifactId>
			<version>${swt.version}</version>
			<scope>compile</scope>
		</dependency>
		<!--dependencies needed to be included at runtime. The classpath loader will filter them.-->
		<dependency>
			<groupId>org.eclipse.swt</groupId>
			<artifactId>org.eclipse.swt.win32.win32.x86</artifactId>
			<version>${swt.version}</version>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.eclipse.swt</groupId>
			<artifactId>org.eclipse.swt.win32.win32.x86_64</artifactId>
			<version>${swt.version}</version>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.eclipse.swt</groupId>
			<artifactId>org.eclipse.swt.cocoa.macosx.x86_64</artifactId>
			<version>${swt.version}</version>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.eclipse.swt</groupId>
			<artifactId>org.eclipse.swt.gtk.linux.x86</artifactId>
			<version>${swt.version}</version>
			<scope>runtime</scope>
		</dependency>
	</dependencies>
	<!-- https://github.com/playn/playn/blob/master/java-swt/pom.xml -->
	<!-- NOTE: this only works for the developer's workstation; if you are going 
		to deploy a real app using the swt-java backend, you have to include all 
		of the jars and select the right one outside of Java, or do even more jiggery 
		pokery as described here: http://stackoverflow.com/questions/2706222/create-cross-platform-java-swt-application -->
	<profiles>
		<profile> <!-- Linux -->
			<id>gtk_linux_x86</id>
			<activation>
				<os>
					<name>linux</name>
					<arch>i386</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.gtk.linux.x86</swt.artifactId>
			</properties>
		</profile>
		<profile>
			<id>gtk_linux_x86_64</id>
			<activation>
				<os>
					<name>linux</name>
					<arch>x86_64</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.gtk.linux.x86_64</swt.artifactId>
			</properties>
		</profile>
		<profile>
			<id>gtk_linux_amd64</id>
			<activation>
				<os>
					<name>linux</name>
					<arch>amd64</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.gtk.linux.x86_64</swt.artifactId>
			</properties>
		</profile>
		<profile> <!-- Windows -->
			<id>win32_x86</id>
			<activation>
				<os>
					<family>windows</family>
					<arch>x86</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.win32.win32.x86</swt.artifactId>
			</properties>
		</profile>
		<profile>
			<id>win32_x86_64</id>
			<activation>
				<os>
					<family>windows</family>
					<arch>x86_64</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.win32.win32.x86_64</swt.artifactId>
			</properties>
		</profile>
		<profile>
			<id>win32_x86_amd64</id>
			<activation>
				<os>
					<family>windows</family>
					<arch>amd64</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.win32.win32.x86_64</swt.artifactId>
			</properties>
		</profile>
		<profile> <!-- Mac OS X -->
			<id>cocoa_macosx_x86</id>
			<activation>
				<os>
					<name>mac os x</name>
					<arch>i386</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.cocoa.macosx</swt.artifactId>
			</properties>
		</profile>
		<profile>
			<id>cocoa_macosx_x86_64</id>
			<activation>
				<os>
					<name>mac os x</name>
					<arch>x86_64</arch>
				</os>
			</activation>
			<properties>
				<swt.artifactId>org.eclipse.swt.cocoa.macosx.x86_64</swt.artifactId>
			</properties>
		</profile>
	</profiles>
	<repositories>
		<repository>
			<id>jcenter-bintray</id>
			<name>Bintray JCenter Maven Repository</name>
			<layout>default</layout>
			<url>https://jcenter.bintray.com/</url>
			<releases>
				<enabled>true</enabled>
			</releases>
			<snapshots>
				<enabled>false</enabled>
			</snapshots>
		</repository>
	</repositories>
</project>

How it works

A classloader will serve classes from all the dependency libraries stored in lib folder in the jar.

How to build and release

mvn release:prepare release:perform -DskipTests=true -Prelease -Darguments="-DskipTests=true -Prelease"

Credits

Other solutions

Other similar techniques that don't work properly:

There are three common methods for constructing an uber-JAR:

Unshaded. Unpack all JAR files, then repack them into a single JAR. * Pro: Works with Java's default class loader. * Con: Files present in multiple JAR files with the same path (e.g., META-INF/services/javax.script.ScriptEngineFactory) will overwrite one another, resulting in faulty behavior. * Tools: Maven Assembly Plugin, Classworlds Uberjar
Shaded. Same as unshaded, but rename (i.e., "shade") all packages of all dependencies. * Pro: Works with Java's default class loader. Avoids some (not all) dependency version clashes. * Con: Files present in multiple JAR files with the same path (e.g., META-INF/services/javax.script.ScriptEngineFactory) will overwrite one another, resulting in faulty behavior. * Tools: Maven Shade Plugin
JAR of JARs. The final JAR file contains the other JAR files embedded within. * Pro: Avoids dependency version clashes. All resource files are preserved. * Con: Needs to bundle a special "bootstrap" classloader to enable Java to load classes from the wrapped JAR files. Debugging class loader issues becomes more complex.
Tools: Eclipse JAR File Exporter, One-JAR.

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A custom classloader to be used from maven generated artifacts to allow executable jars and custom exclusion of some libraries at runtime (eg. swt libraries). Based on code and packing strategy from eclipse.

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