Maven no class def found when using SNAPSHOT dependency

Question

I'm building an app for RaspberryPi that uses Pi4j. It worked fine until I encountered a need to change Pi4j version from 1.1 to 1.2-SNAPSHOT. I get NoCassDefFoundException when using SNAPSHOT only.

I'm using a few plugins to separate my jar and all libraries, which are stored in lib/* directory. maven-dependency-plugin does the job

maven-jar-plugin links directory with libs to my jar

maven-antrun-plugin copies my jar and only changed dependencies to my raspberry during mvn install

My pom.xml file (stripped a lot)

<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>Rpi</groupId>
<artifactId>Rpi</artifactId>
<version>0.0.1-SNAPSHOT</version>

<properties>
    <!--<pi4j.version>1.2-SNAPSHOT</pi4j.version>-->
    <pi4j.version>1.1</pi4j.version>
</properties>

<dependencies>
    <dependency>
        <groupId>com.pi4j</groupId>
        <artifactId>pi4j-core</artifactId>
        <version>${pi4j.version}</version>
    </dependency>
    (...)
</dependencies>

<repositories>
    <repository>
        <id>oss-snapshots-repo</id>
        <name>Sonatype OSS Maven Repository</name>
        <url>https://oss.sonatype.org/content/groups/public</url>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
</repositories>

<build>
    <sourceDirectory>src</sourceDirectory>
    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.6.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <executions>
                <execution>
                    <id>copy-dependencies</id>
                    <phase>prepare-package</phase>
                    <goals>
                        <goal>copy-dependencies</goal>
                    </goals>
                    <configuration>
                        <outputDirectory>${project.build.directory}/lib</outputDirectory>
                        <overWriteReleases>true</overWriteReleases>
                        <overWriteSnapshots>true</overWriteSnapshots>
                        <overWriteIfNewer>true</overWriteIfNewer>
                    </configuration>
                </execution>
            </executions>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>
            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>true</addClasspath>
                        <classpathPrefix>lib/</classpathPrefix>
                        <mainClass>${pi.main.class}</mainClass>
                    </manifest>
                </archive>
            </configuration>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-antrun-plugin</artifactId>
            <version>1.8</version>
            <executions>
                <execution>
                    <phase>install</phase>
                    <goals>
                        <goal>run</goal>
                    </goals>
                    <configuration>
                        <tasks>
                            <scp
                                    file="${project.build.directory}/${project.build.finalName}.jar"
                                    todir="${pi.user}:${pi.password}@${pi.host}:${pi.deployDirectory}"
                                    port="${pi.port}" trust="true" verbose="false" failonerror="false">
                            </scp>

                            <!-- copy dependencies, only new or modified-->
                            <scp todir="${pi.user}:${pi.password}@${pi.host}:${pi.deployDirectory}/lib"
                                 port="${pi.port}" trust="true" verbose="false" failonerror="false">
                                <fileset dir="${project.build.directory}/lib">
                                    <modified>
                                        <param name="cache.cachefile" value="localdev.cache"/>
                                    </modified>
                                </fileset>
                            </scp>

                        </tasks>
                    </configuration>
                </execution>
            </executions>
            <dependencies>
                <dependency>
                    <groupId>org.apache.ant</groupId>
                    <artifactId>ant-jsch</artifactId>
                    <version>1.9.6</version>
                </dependency>
            </dependencies>
        </plugin>
        (...)
    </plugins>
</build>

After mvn install everything looks fine, my jar is where it should be, all dependencies are copied, I run my jar using java -jar Rpi-0.0.1-SNAPSHOT.jar and it runs, until a NoClassDefFoundError gets raised.

The problem is when I use Pi4j 1.2-SNAPSHOT only. When I use version 1.1 it works fine (well, crashes, that's why I have to switch to 1.2-SNAPSHOT). If I use version 1.1 in pom.xml and after mvn install rename lib\pi4j-core-1.2-SNAPSHOT.jar to lib\pi4j-core-1.1.jar everything runs as expected, no crashes, using version 1.2...

Answer 1

Maven-jar-plugin changed name of SNAPSHOT dependency in my jar classpath. To fix this I had to add <useUniqueVersions>false</useUniqueVersions> to the plugin manifest, so now it looks like this

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>
            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>true</addClasspath>
                        <classpathPrefix>lib/</classpathPrefix>
                        <mainClass>${pi.main.class}</mainClass>
                        <useUniqueVersions>false</useUniqueVersions>
                    </manifest>
                </archive>
            </configuration>
        </plugin>

and works fine