Maven assembly plugin - ignore 'archive cannot be empty'

Question

I have problem with assembly plugin. I have to use one assembly definition which create JAR file for more modules. So project structure looks like this

module/
----module1/
-------- pom.xml
----module2/
-------- pom.xml
----moduleX/
-------- pom.xml
assembly_jar.xml
pom.xml (this is parent)

Parent pom file looks like following:

<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.my.project</groupId>
    <artifactId>parent-module</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <executions>
                  <execution>
                    <id>make-jar</id>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                    <configuration>
                        <attach>false</attach>
                        <descriptors>
                            <descriptor>${source-systems.basedir}/assembly_jar.xml</descriptor>
                        </descriptors>
                        <finalName>${project.artifactId}-${project.version}</finalName>
                        <appendAssemblyId>false</appendAssemblyId>
                    </configuration>
                </execution>
            </plugin>
        </plugins>
    </build>
</project>

assembly_jar.xml looks like following:

<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>jar-with-some-dependencies</id>
  <formats>
    <format>jar</format>
  </formats>
  <includeBaseDirectory>false</includeBaseDirectory>
  <dependencySets>
    <dependencySet>
      <outputDirectory>/</outputDirectory>
      <useProjectArtifact>true</useProjectArtifact>
      <scope>runtime</scope>
      <unpack>true</unpack>
    </dependencySet>
  </dependencySets>
</assembly>

pom file of module 1 looks like this:

<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>

  <parent> 
    <groupId>com.my.project</groupId>
    <artifactId>parent-module</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <relativePath>../pom.xml</relativePath>
  </parent>

  <packaging>pom</packaging>
  <groupId>com.my.project</groupId>
  <artifactId>module1</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <name>oracle_rds</name>

  <dependencies>
    <dependency>
      <groupId>com.oracle</groupId>
      <artifactId>ojdbc6</artifactId>
      <version>11.2.0.4</version>
    </dependency>
  </dependencies>

</project>

When I run mvn clean install for module1 everything works fine and jar file is created. But then I have module2 which does not need any particular dependencies. So pom file looks like this:

<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>

  <parent> 
    <groupId>com.my.project</groupId>
    <artifactId>parent-module</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <relativePath>../pom.xml</relativePath>
  </parent>

  <packaging>pom</packaging>
  <groupId>com.my.project</groupId>
  <artifactId>module2</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <name>oracle_rds</name>

</project>

When I run mvn clean install I have error Error creating assembly archive jar-with-some-dependencies: archive cannot be empty It is because there is no dependency to pack into jar file.

Is there any way how to ignore this error and do not create jar file if there are not dependencies in module?

I do not want to move assembly definition into module because of big duplicity (I will have more then 100 modules and mostly of them will have some special dependencies) Thanks for help.

Answer 1

I was able to work around this by adding a dummy folder: Can I create empty directories while packaging using maven-assembly-plugin?

<fileSet>
    <directory>${project.build.directory}</directory>
    <outputDirectory>empty_folder</outputDirectory>
    <excludes>
        <exclude>**/*</exclude>
    </excludes>
</fileSet>

This solution does not require any configuration outside of the descriptor, which makes it pretty clean.

I also have a multi-module project made up of sub-assemblies that get wrapped up in a master assembly. However some of the sub-assemblies are only valid on a specific OS (windows), which is simply denoted by having no content for the other OS'. An empty archive being produced by the sub-assembly is preferred in my case so that dependencies from the master assembly to all sub-assemblies are valid independent of platform. The master-assembly is uneffected by the empty directory since it doesn't match any of its assembly inclusions.

Answer 2

Yes, it works.

In my old configuration, It looks to include all files and folders at de ${basedir}/build/, and there is no output directory configured.