How to bundle a JAR file with its dependencies using maven

I am developing a Java agent using ByteBuddy, and I need the ByteBuddy library .jar file to be included in the agent .jar file. So far, in order for the agent to run smoothly, I need the ByteBuddy library .jar files to be present in the classpath both at compile time and at runtime. How can I bundle a .jar file such that the agent is self-contained ?

I tried using the shade plugin (as demonstrated here) as well as a few other techniques found on the web, but none of them seem to really include the dependencies in the .jar file, only a reference.

For every technique, I looked in the resulting .jar file (weighs around 5kB every time) and only found the .class files corresponding to the classes I had written, no class files related to ByteBuddy. To be clear, the ByteBuddy library .jar file weighs about 3MB, so I expect my self-contained agent .jar file to weigh around 3MB, as my code is light.

Below is my pom.xml file :

<?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>

  <groupId>com.captainhook.agent</groupId>
  <artifactId>agent</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>agent</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>net.bytebuddy</groupId>
      <artifactId>bytebuddy</artifactId>
      <version>1.12.3</version>
      <scope>system</scope>
      <systemPath>${project.basedir}/byte-buddy-1.12.3.jar</systemPath>
   </dependency>
   <dependency>
    <groupId>net.bytebuddy.agent</groupId>
    <artifactId>bytebuddy-agent</artifactId>
    <version>1.12.3</version>
    <scope>system</scope>
    <systemPath>${project.basedir}/byte-buddy-agent-1.12.3.jar</systemPath>
 </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <executions>
          <execution>
            <phase>package</phase>
            <goals>
              <goal>single</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

And this is the output I get after running mvn package :

[...]
[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ agent ---
[INFO] 
[INFO] --- maven-assembly-plugin:2.2-beta-5:single (default) @ agent ---
[INFO] Building jar: /home/bluesheet/svn/stages/captainhook/2021/ijp-frida-jdi-bytebuddy/1/dbg/shared/agent/maven-test/agent/target/agent-1.0-SNAPSHOT-jar-with-dependencies.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.339 s
[INFO] Finished at: 2021-12-31T12:26:59+01:00
[INFO] ------------------------------------------------------------------------

EDIT: So, the reason why all the previous techniques were not working was because of the way I specified the dependencies. This doesn’t get included :

<dependency>
    <groupId>net.bytebuddy</groupId>
    <artifactId>bytebuddy</artifactId>
    <version>1.12.3</version>
    <scope>system</scope>
    <systemPath>${project.basedir}/byte-buddy-1.12.3.jar</systemPath>
</dependency>

while this does :

<dependency>
    <groupId>net.bytebuddy</groupId>
    <artifactId>byte-buddy</artifactId>
    <version>1.12.6</version>
</dependency>

I am new to maven so I blindly copy-pasted a piece of code to include the dependencies and I did not spot the error… Thank you very much !

Answer

Sounds like you need to use the “maven-assembly-plugin” with the “jar-with-dependencies” descriptor.

E.g. here is a full example pom file with a dependency on ByteBuddy:

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test.example</groupId>
    <artifactId>packaging-example</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4.1</version>
                <configuration>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                    <archive>
                        <manifest>
                            <mainClass>test.example.TestByteBuddy</mainClass>
                        </manifest>
                    </archive>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>

        </plugins>
    </build>

    <dependencies>

        <dependency>
            <groupId>net.bytebuddy</groupId>
            <artifactId>byte-buddy</artifactId>
            <version>1.12.6</version>
        </dependency>

    </dependencies>

</project>

And for the sake of completeness – here is the main class also :

package test.example;

import net.bytebuddy.ByteBuddy;

public class TestByteBuddy
{
    public static void main(String... args) throws Exception
    {
        System.out.println("Hello Byte Buddy Class - " + ByteBuddy.class);
    }
}

Building this will produce an additional file in the target directory – packaging-example-1.0-SNAPSHOT-jar-with-dependencies.jar

Then you should be able to run it simply with :

java -jar packaging-example-1.0-SNAPSHOT-jar-with-dependencies.jar 

to give you the output:

Hello Byte Buddy Class - class net.bytebuddy.ByteBuddy