Libraries not loaded in executable jar

Question

I have the following maven configuration

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.0</version>
            <configuration>
                <source>${maven.compiler.source}</source>
                <target>${maven.compiler.target}</target>
                <release>${java.version}</release>
            </configuration>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-assembly-plugin</artifactId>
            <configuration>
                <source>${maven.compiler.source}</source>
                <target>${maven.compiler.target}</target>
                <appendAssemblyId>false</appendAssemblyId>
                <descriptors>
                    <descriptor>src/main/assembly/assembly.xml</descriptor>
                </descriptors>
                <archive>
                    <manifest>
                        <mainClass>${main.class}</mainClass>
                        <addClasspath>true</addClasspath>
                        <classpathPrefix>lib/</classpathPrefix>
                        <classpathLayoutType>repository</classpathLayoutType>
                        <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
                        <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>
                    </manifest>
                    <manifestEntries>
                        <Class-Path>./lib/*.jar</Class-Path>
                    </manifestEntries>
                </archive>
            </configuration>
            <executions>
                <execution>
                    <id>make-assembly</id>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>

assembly.xml:

<assembly>
    <id>assembly</id>
    <formats>
        <format>jar</format>
    </formats>
    <includeBaseDirectory>false</includeBaseDirectory>
    <dependencySets>
        <dependencySet>
            <outputDirectory>/</outputDirectory>
            <unpack>true</unpack>
            <includes>
                <include>com.relax-gaming.casinoworld:casinoworld</include>
            </includes>
        </dependencySet>
        <dependencySet>
            <outputDirectory>lib</outputDirectory>
            <unpack>false</unpack>
            <excludes>
                <exclude>com.relax-gaming.casinoworld:casinoworld</exclude>
            </excludes>
        </dependencySet>
    </dependencySets>
</assembly>

my manifest content is:

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: Apache Maven
Built-By: username
Build-Jdk: 11
Specification-Title: project title
Specification-Version: 0.0.1-SNAPSHOT
Implementation-Title: Project title
Implementation-Version: 0.0.1-SNAPSHOT
Implementation-Vendor-Id: groupid
Main-Class: path.to.main.class
Class-Path: ./lib/*.jar

My jar is bundled as follows:

-my.code.package (from src/main/java)
+ META-INF
- MANIFEST.MF  (where the above configuration is)
+ lib
- dep1.jar (all the dependencies as jar files)
-my.resources.file (from src/main/resources)

When i run the file using java -jar i get NoClassDefFound errosr cause the libraries are not loaded.

I imagine that the thing wrong is my classpath inside the manifest file. What should it be ?

Answer 1

So, Turns out you kinda can't.

My solution was as follows:

update the assembly.xml and pom.xml as follows:

assembly:

<assembly>
    <id>assembly</id>
    <formats>
        <format>jar</format>
    </formats>
    <includeBaseDirectory>false</includeBaseDirectory>
    <dependencySets>
        <dependencySet>
            <outputDirectory>/</outputDirectory>
            <unpack>true</unpack>
            <excludes>
                <exclude>groupId:artifactIdOfResourceIWant</exclude>
            </excludes>
        </dependencySet>
        <dependencySet>
            <outputDirectory>lib-packed</outputDirectory>
            <unpack>false</unpack>
            <includes>
                <include>groupId:artifactIdOfResourceIWant</include>
            </includes>
        </dependencySet>
    </dependencySets>
</assembly>

pom :

<plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-assembly-plugin</artifactId>
                    <configuration>
                        <source>${maven.compiler.source}</source>
                        <target>${maven.compiler.target}</target>
                        <appendAssemblyId>false</appendAssemblyId>
                        <descriptors>
                            <descriptor>src/main/assembly/assembly.xml</descriptor>
                        </descriptors>
                        <archive>
                            <manifest>
                                <mainClass>${main.class}</mainClass>
                                <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
                                <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>
                            </manifest>
                        </archive>
                    </configuration>
                    <executions>
                        <execution>
                            <id>make-assembly</id>
                            <phase>package</phase>
                            <goals>
                                <goal>single</goal>
                            </goals>
                        </execution>
                    </executions>
                </plugin>

This basically unpacks all dependencies normally, but leaves the specific one you need to remain unpacked as a jar file within the jar file. This reduces complexity to only the jars you need unpacked.

now, the issue with that still remains that Class-Path can only take dir/* syntax to load all jars externally, and it cannot be used to load a jarfile (even with specific names) So to leave the jar bundled inside and have it automatically loaded i basically need to modify my code to have a custom classloader that reads that file.