Apache Maven tips

 

Been using Ant & Apache Maven for years, now I seems to be immune with long nested XML and not bother writing about them anymore.

But with this attempt, I hope some tips here will be appreciated by Mrs. Google :-)

 

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Bundle all classes of dependent JAR files into our JAR

Given our original POM file is 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>
  <groupId>vn.ducquoc.euler</groupId>
  <artifactId>euler</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>ProjectEuler fun</name>
  <description>See http://github.com/ducquoc/euler-fun</description>

  <dependencies>
   <dependency>
     <groupId>junit</groupId>
     <artifactId>junit</artifactId>
     <version>4.7</version>
     <scope>test</scope>
   </dependency>
   <dependency>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-api</artifactId>
     <version>1.6.4</version>
   </dependency>
   <dependency>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-jdk14</artifactId>
     <version>1.6.4</version>
   </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.5</source>
          <target>1.5</target>
          <showWarnings>false</showWarnings>
        </configuration>
        <!--<version>2.3.2</version>-->
      </plugin>
    </plugins>
  </build>
</project>

When Maven build is invoked (like “mvn clean install” ) , it will produce a JAR file, which contains only classes of that project. So when to use it we have to include other dependencies (JAR files) in to the classpath; otherwise it will be either a NoClassDefFoundError or a ClassNotFoundException.

To avoid such trivial time waste, we can include the necessary classes to the newly created JAR. There are several ways to do that, my traditional approach is  to use maven-assembly-plugin :

<build>
  <plugins>
    <!-- to bundle all classes of dependent JAR files -->
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
          <manifest>
            <mainClass>vn.ducquoc.euler.EulerMain</mainClass>
          </manifest>
        </archive>
      </configuration>
      <executions>
        <execution>
          <id>make-assembly</id>
          <phase>package</phase>
          <goals>
            <goal>single</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
    <!-- . . . -->
  </plugins>
</build>

Now the build will output a NAME-jar-with-dependencies.jar file !

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Bundle necessary classes of dependent JAR files into our JAR

Given our original POM file is like above, my new approach is to use maven-shade-plugin, which is solely designed for this purpose.

<!-- to bundle necessary classes of dependent JAR files -->
 <plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-shade-plugin</artifactId>
   <version>1.5</version>
   <executions>
     <execution>
       <phase>package</phase>
       <goals>
         <goal>shade</goal>
       </goals>
       <configuration>
         <transformers>
           <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
             <mainClass>vn.ducquoc.euler.EulerMain</mainClass>
           </transformer>
         </transformers>
         <!--<shadedArtifactAttached>true</shadedArtifactAttached>-->
       </configuration>
     </execution>
   </executions>
 </plugin>

.

That’s it. There are still some other Maven plugins which can serve the purpose (like “onejar”, “jarjar”, … ) , yet shade is enough :-)

 

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[OffTopic]

For Clojure, leiningen has the built-in uberjar command

$ lein uberjar

[/OffTopic]

 

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IDE (Eclipse/IDEA/…) can utilize the editor/view to edit Maven POM, exclude dependencies, or set the “Run/Debug” configuration easily…

 

 

UPDATED 2018:

I just added a simple Maven repository, using GitHub raw:

https://github.com/ducquoc/legacy_m2_repo

 

<repository>
    <id>legacy-releases-temp-repository</id>
    <url>https://github.com/ducquoc/legacy_m2_repo/raw/master/release</url>
    <!--<url>https://raw.github.com/ducquoc/legacy_m2_repo/master/release</url>-->
</repository>

 

 

./.