sweat123 / fat-jar-isolation

Java class isolation with fat jar

Fat Jar Plugin

A maven plugin for creating fat jar;

All of the libraries for the current project will be added into the fat jar including current project jar file;

usage

<plugin>
    <groupId>com.laomei.github</groupId>
    <artifactId>fat-jar-plugin</artifactId>
    <version>1.0-SNAPSHOT</version>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>repackage</goal>
            </goals>
        </execution>
    </executions>
</plugin>

result

A new jar file will be created which the name will be append '-fat' at the end of the name;

The structure of fat jar

.
├── lib
│   ├── demo-1.0-SNAPSHOT.jar
│   ├── spring-core-4.3.17.RELEASE.jar
└── META-INF
    └── MANIFEST.MF

• demo-1.0-SNAPSHOT.jar jar file of the current project
• spring-core-4.3.17.RELEASE.jar jar file that declared in the pom.xml

Fat Jar ClassLoader

The classloader that can load class from fat jar;

One fat jar corresponds to one FatJarClassLoader; The project which contains multiple fat jar will has multiple FatJarClassLoader;

In fact users should use FatJarDelegateClassLoader which will manage all FatJarClassLoader;

FatJarDelegateClassLoader expected 3 args in constructors:

1. urls
2. parent classloader
3. the prefix name for class which will be load by FatJarDelegateClassLoader

FatJarClassLoader was write with spring-boot-loader;

How to use

xxx.jar is a project jar file witch contains some fat jars; We only need to give the xxx.jar url to FatJarDelegateClassLoader; FatJarDelegateClassLoader will search all fat jar files in the giving urls and creating multiple FatJarClassLoader; The class which name is begin with com.xxx will be load by FatJarDelegateClassLoader;

URL url = lastClassLoader.getResource("xxx.jar");
new FatJarDelegateClassLoader(
        new URL[] { url },
        null,
        Collections.singleton("com.xxx")
);