Manually attach main artifact if built by maven-assembly-plugin

Question

I am having problems building a maven project. I have a requirement to produce deterministic jar files, which must be binary-consistent across different builds and versions, in case there are no source code changes in between these builds. For the purpose, I have used this article for guidance.

I have successfully managed to build my jars and they are consistent up to my requirements. Here is my configuration:

  <plugin>
    <artifactId>maven-antrun-plugin</artifactId>
    <version>1.7</version>
    <executions>
      <execution>
        <id>step-1-remove-timestamp</id>
        <phase>prepare-package</phase>
        <configuration>
          <target>
            <touch datetime="01/01/2015 00:10:00 am">
              <fileset dir="target/classes"/>
              <fileset dir="src"/>
            </touch>
          </target>
        </configuration>
        <goals>
          <goal>run</goal>
        </goals>
      </execution>
      <execution>
        <id>step-3-rename-assembly</id>
        <phase>package</phase>
        <configuration>
          <target>
            <copy file="${project.build.directory}/${project.build.finalName}-deterministic.zip"
                  tofile="${project.build.directory}/${project.build.finalName}.jar"/>
          </target>
        </configuration>
        <goals>
          <goal>run</goal>
        </goals>
      </execution>
    </executions>
  </plugin>

  <plugin>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>2.2.1</version>
    <configuration>
      <descriptors>
        <descriptor>src/main/assembly/zip.xml</descriptor>
      </descriptors>
    </configuration>
    <executions>
      <execution>
        <id>step-2-make-assembly</id>
        <phase>prepare-package</phase>
        <goals>
          <goal>single</goal>
        </goals>
      </execution>
    </executions>
  </plugin>

In the above code I build and package the jar as a zip, then copy the zip over the expected jar artifact.
The problem with the above, is that maven still executes the maven-jar-plugin, so the manually assembled jar is overwritten by the one of the maven-jar-plugin. I do not want to use this jar, since it is not consistent with my requirements.

So, I have disabled the maven-jar-plugin execution, by explicitly setting it to run for an invalid phase, like below: (saw that from other posts here)

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>2.5</version>
    <executions>
      <execution>
        <id>default-jar</id>
        <phase>never</phase>
        <configuration>
          <finalName>unwanted</finalName>
          <classifier>unwanted</classifier>
        </configuration>
      </execution>
    </executions>
  </plugin>

Everything seems fine, until I discovered my main jar artifact is never installed in the .m2 directory. To correct this, I also added the maven-helper-plugin so that I manually attach any artifacts I produce from the assembler plugin:

  <plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <version>1.9.1</version>
    <executions>
      <execution>
        <id>attach-instrumented-jar</id>
        <phase>verify</phase>
        <goals>
          <goal>attach-artifact</goal>
        </goals>
        <configuration>
          <artifacts>
            <artifact>
              <file>${project.build.directory}/${project.build.finalName}.jar</file>
              <type>jar</type>
            </artifact>
          </artifacts>
        </configuration>
      </execution>
    </executions>
  </plugin>

This leads to an error I am unable to solve:

[ERROR] Failed to execute goal org.codehaus.mojo:build-helper-maven-plugin:1.9.1:attach-artifact (attach-instrumented-jar) on project my-project: Execution attach-instrumented-jar of goal org.codehaus.mojo:build-helper-maven-plugin:1.9.1:attach-artifact failed: For artifact {full-name-of-my-project.jar}: An attached artifact must have a different ID than its corresponding main artifact. -> [Help 1]

Is there a way to overcome this issue? I've checked for solutions, and most recommend using classifiers, but I want to install the main artifact as would the maven-jar-plugin. Other software we are developing will require the standard jar dependency, and we want to avoid complicating our setup by introducing classifiers unreasonably.

Answer 1

After some more trial and failures I happened to come with a working solution. I am posting it here with the hopes to either be useful, or to have any issues with pointed to me, as I am not really confident if this is a reliable approach.

So, the error I received

An attached artifact must have a different ID than its corresponding main artifact.

meant to me that I cannot manually install "again" the main artifact. Since that artifact is not produced anymore by the maven-jar-plugin, it never gets scheduled for installation even if the file is present (the antrun copy task produces a jar with the same name).

Surprisingly, it needed a few little tricks to make this work again:

1. Re-enabled the maven-jar-plugin as it should be:

   <plugin>
     <groupId>org.apache.maven.plugins</groupId>
     <artifactId>maven-jar-plugin</artifactId>
     <version>2.5</version>
     <executions>
       <execution>
         <id>default-jar</id>
         <phase>package</phase>
       </execution>
     </executions>
   </plugin>
   

   This will produce the standard jar on the package phase, and most importantly, makes maven aware for it to be installed during the install phase.

2. Tweak the maven-antrun-plugin copy tasks to overwrite the already produced jar with the deterministic zip. The setup is nearly identical as in my question, so I am only adding the differences:

   <plugin>
     <artifactId>maven-antrun-plugin</artifactId>
     <version>1.7</version>
     <executions>
       <execution>...</execution>
       <execution>
         <id>step-3-rename-assembly-and-sources</id>
         <phase>package</phase>
         <configuration>
           <target>
             <copy file="${project.build.directory}/${project.build.finalName}-deterministic.zip"
                   tofile="${project.build.directory}/${project.build.finalName}.jar"
                   overwrite="true"/>
           </target>
         </configuration>
       </execution>
         . . .
     </executions>
   </plugin>
   

   The copy operation now has overwrite="true" specified. Originally, the copy operation seemed to ignore files in the destination if they already exist, and what happened is that the maven-jar-plugin had already produced the default jar artifact when the copying occured. With this option set, the maven-antrun-plugin now overrides the former jar with the deterministic one, and the latter becomes a subject of the maven install phase.

3. Removed the setup from the build-helper-maven-plugin, so that the main jar artifact is not copied a second time:

            <artifact>
              <file>${project.build.directory}/${project.build.finalName}.jar</file>
              <type>jar</type>
            </artifact>

That's it, the correct jar is installed in the .m2 dir.

Answer 2

In case you don't have a plugin to create and attach main artifact for you, there is a more generic solution with Groovy Maven plugin:

<plugin>
    <groupId>org.codehaus.gmaven</groupId>
    <artifactId>groovy-maven-plugin</artifactId>
    <version>2.1</version>
    <executions>
        <execution>
            <id>set-main-artifact</id>
            <phase>package</phase>
            <goals>
                <goal>execute</goal>
            </goals>
            <configuration>
                <source>
                    project.artifact.setFile(new File(project.build.directory, project.build.finalName + ".zip"))
                </source>
            </configuration>
        </execution>
    </executions>
</plugin>

Inspired by post https://stackoverflow.com/a/31513690/2053580 many thanks to https://stackoverflow.com/users/1314907/lukasz-guminski