Maven: Attaching multiple artifacts

Question

I have a maven project that uses some custom jars [not found in any repository]. To add them along with the Maven build I am using the attach-artifact goal in maven. Following is my pom file:

<?xml version="1.0" encoding="UTF-8"?>
<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.maximus</groupId>
  <artifactId>adminbuild</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  <name>adminbuild</name>

  <build>
    <sourceDirectory>src/main/java</sourceDirectory>
    <testSourceDirectory>src/test/java</testSourceDirectory>
    <outputDirectory>target</outputDirectory>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <version>1.7</version>
        <executions>
          <execution>
            <id>attach-artifacts</id>
            <phase>package</phase>
            <goals>
              <goal>attach-artifact</goal>
            </goals>
            <configuration>
              <artifacts>
                <artifact>
                  <file>${basedir}/../../resources/dependencies/java/customjar1.jar</file>
                  <type>jar</type>
                </artifact>
                <artifact>
                  <file>${basedir}/../../resources/dependencies/java/customjar2.jar</file>
                  <type>jar</type>
                </artifact>
              </artifacts>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

My projects that use these jars [customjar1.jar, customjar2.jar] have their dependency on the above pom file [adminbuild].

When I execute the mvn clean install command, I get the following error:

[ERROR] Failed to execute goal org.codehaus.mojo:build-helper-maven-plugin:1.7:attach-artifact (attach-artifacts) on project adminbuild: The artifact with same type and classifier: jar:null is used more than once. -> [Help 1]

Following is the output of mvn -version command:

Apache Maven 3.0.3 (r1075438; 2011-02-28 23:01:09+0530)
Maven home: C:\maven
Java version: 1.6.0_26, vendor: Sun Microsystems Inc.
Java home: C:\Java\jdk1.6.0_26\jre
Default locale: en_IN, platform encoding: Cp1252
OS name: "windows 7", version: "6.1", arch: "amd64", family: "windows"

It seems that the way I am attaching the artifacts is incorrect. Should I not attach multiple artifacts in the same pom file? If yes then how. Please help.

Answer 1

Attached artifacts are normally used to install additional files created by your build, like the classes jar of a webapp, documentation or sources.

To add files to your maven repository so they are available as dependencies you should use the install-file goal.

Edit: Attached artifacts are identified by the same groupId and artifactId as your main project but with a different classifier. In your configuration, you did not specify the classifier, hence the error message.

Answer 2

You would want to have these custom jars in a repository manager like nexus so that they can be downloaded/used like a normal dependency jar.

Assuming that is not possible and seeing that these jars are in well-known location, perhaps you could specify these custom jars with system scope in the projects that need them?

<project>
  ...
  <dependencies>
    <dependency>
      <groupId>my-group</groupId>
      <artifactId>customjar1</artifactId>
      <version>a.b.c</version>
      <scope>system</scope>
      <systemPath>${basedir}/../../resources/dependencies/java/customjar1.jar</systemPath>
    </dependency>
  </dependencies>
  ...
</project>