How can I use Maven to generate a JAR file from the contents of a directory I specify?

I'm using the maven-deploy-plugin to deploy a third party jar (previously downloaded to my target directory from a plugin not show here) to Nexus as the name 'third-party-1.0.jar', this all works fine using the configuration below.

I also have a javadoc directory in my target directory, which is the javadoc for this third party jar. I'd like to package that javadoc directory as 'third-party-1.0-javadoc.jar'.

If I could get the directory packaged as a JAR, I think I could the javadoc parameter of the deploy plugin below to deploy it, just unsure how to package a custom directory as a JAR with a specific name using Maven, maybe the assembly plugin?

TLDR; How do I use Maven to create a JAR file from the contents of a directory I specify?

<plugin>
    <artifactId>maven-deploy-plugin</artifactId>
    <version>2.8.2</version>
    <executions>
        <execution>
            <id>default-deploy</id>
            <phase>none</phase>
        </execution>

        <execution>
             <id>deploy-jar</id>
             <phase>deploy</phase>
             <goals>
                 <goal>deploy-file</goal>
             </goals>
             <configuration>
             <file>${project.build.directory}/code.jar</file>
             <url>...</url>
             <repositoryId>...</repositoryId>  
             <url>...</url>            
             <packaging>jar</packaging>
             <generatePom>true</generatePom>
             <groupId>com.example</groupId>
             <artifactId>third-party</artifactId>
             <version>1.0</version> 
             </configuration>     
        </execution>
    </executions>
</plugin>

I ended up using the maven-assembly-plugin instead of the maven-jar-plugin as it allows more control over the resulting JAR, including not adding a pom.xml to it, not attaching it to the project as an artifact to be deployed (attach=false), and how it is named. This allows the maven-deploy-plugin to control how it is deployed, and what Maven coordinates to use when deploying it.

I can then just attach the Javadoc JAR built with the assembly plugin into my deploy file execution using the javadoc tag:

src/main/assembly/assembly.xml

<assembly xmlns="http://maven.apache.org/ASSEMBLY/2.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/ASSEMBLY/2.0.0 http://maven.apache.org/xsd/assembly-2.0.0.xsd">
    <id>package-third-party-javadoc</id>
    <formats>
        <format>jar</format>
    </formats>
    <includeBaseDirectory>false</includeBaseDirectory>
    <fileSets>
        <fileSet>
            <directory>${project.build.directory}/dir</directory>  
            <outputDirectory>.</outputDirectory>
        </fileSet>
    </fileSets>
</assembly>

pom.xml

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>3.1.1</version>
    <executions>
        <execution>
            <id>package-third-party-javadoc</id>
            <phase>compile</phase>
            <goals>
                <goal>single</goal>
            </goals>
            <configuration>
                <descriptors>
                    <descriptor>src/main/assembly/assembly.xml</descriptor>
                </descriptors>
                <finalName>third-party-javadoc</finalName>
                <appendAssemblyId>false</appendAssemblyId>
                <attach>false</attach>  
            </configuration>
        </execution>
    </executions>
</plugin>

<plugin>
    <artifactId>maven-deploy-plugin</artifactId>
    <version>2.8.2</version>
    <executions>
        <execution>
            <id>default-deploy</id>
            <phase>none</phase>
        </execution>

        <execution>
            <id>deploy-jar</id>
            <phase>deploy</phase>
            <goals>
                <goal>deploy-file</goal>
            </goals>
            <configuration>
                <file>${project.build.directory}/code.jar</file>
                <url>...</url>
                <repositoryId>...</repositoryId>  
                <url>...</url>            
                <packaging>jar</packaging>
                <generatePom>true</generatePom>
                <groupId>com.example</groupId>
                <artifactId>third-party</artifactId>
                <version>1.0</version> 
                <javadoc>${project.build.directory}/third-party-javadoc.jar</javadoc>
            </configuration>     
        </execution>
    </executions>
</plugin>