I had an external .jar that cannot be imported from public repositories using pom.xml, it's XPTO.jar.

I was able to run the project locally from my IDE and everything worked perfectly. Refer to the library after downloading it as follows:

<dependency>
    <groupId>com.xpto.lib</groupId>
    <artifactId>XPTO</artifactId>
    <version>1.0</version>
    <scope>system</scope>
    <systemPath>${basedir}/lib/XPTO.jar</systemPath>
</dependency>

When I run mvn clean package to create my .jar file and try to run the created .jar, an error will pop up.

I was facing this error and about getting crazy before finding this solution.

Miracle Solution 🙆‍♂️🙆‍♀️

In your pom.xml just add this <includeSystemScope>true</includeSystemScope> like this

<plugins>
    <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <configuration>
            <classifier>exec</classifier>
            <includeSystemScope>true</includeSystemScope>
        </configuration>
    </plugin>
</plugins>

The IDE can easily see the scope of the system by default, however when generating our build we have to force the maven to see this same scope.