[jira] (MJAR-177) Empty string should be treated as default classifier

[Stefan Fussenegger (JIRA)]

Stefan Fussenegger created MJAR-177:
---------------------------------------

             Summary: Empty string should be treated as default classifier
                 Key: MJAR-177
                 URL: https://jira.codehaus.org/browse/MJAR-177
             Project: Maven JAR Plugin
          Issue Type: Bug
    Affects Versions: 2.4
         Environment: $ mvn -version
Apache Maven 3.0.4
Maven home: /usr/share/maven
Java version: 1.7.0_55, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-7-openjdk-amd64/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "3.11.0-14-generic", arch: "amd64", family: "unix"

            Reporter: Stefan Fussenegger


I'm not an expert for Maven internals, but there seem to be subtle differences 
regarding empty properties. Sometimes they are set to null and sometimes they 
remain an empty string (""). The later causes an error when used as classifier

This seems to be the problematic code from AbstratJarMojo.java:

{code:java}
String classifier = getClassifier();
if ( classifier != null ) // ERROR check for empty string
{
    projectHelper.attachArtifact( getProject(), getType(), classifier, jarFile 
);
}
else
{
    getProject().getArtifact().setFile( jarFile );
}
{code}

The resulting error is

{code}
[ERROR] Failed to execute goal 
org.apache.maven.plugins:maven-jar-plugin:2.4:jar (default-jar) on project 
sample-project: Execution default-jar of goal 
org.apache.maven.plugins:maven-jar-plugin:2.4:jar failed: For artifact 
{org.example:sample-project:1.0.0-SNAPSHOT:jar}: An attached artifact must have 
a different ID than its corresponding main artifact. -> [Help 1]
{code}

It's not easy to set a property to "" though as properties from XML will 
typically resolve to null but some plugins do. For example, it's possible to 
use gmaven-plugin to achieve this:

{code:xml}
<plugin>
  <groupId>org.codehaus.gmaven</groupId>
  <artifactId>gmaven-plugin</artifactId>
  <executions>
    <execution>
      <id>artifact-classifier</id>
      <phase>initialize</phase>
      <goals>
        <goal>execute</goal>
      </goals>
      <configuration>
        <source>
          project.properties['artifact.classifier'] = "";
        </source>
      </configuration>
    </execution>
  </executions>
</plugin>
<plugin>
  <artifactId>maven-jar-plugin</artifactId>
  <version>${maven-jar-plugin.version}</version>
  <inherited>true</inherited>
  <configuration>
    <classifier>${artifact.classifier}</classifier>
  </configuration>
</plugin>
{code}



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