Question

I am brand new to both java and to maven, so this is likely very simple.

If I follow the maven2 hello world instructions here:

http://maven.apache.org/guides/getting-started/maven-in-five-minutes.html

everything works OK. If I then alter pom.xml to bring in a dependency from a remote repository, the files for this dependency get stored in ~/.m2/repository/new-dependency/.

Using the syntax in the hello world instructions to run the application requires that I add the absolute path to the dependency to my classpath (either by setting the environment variable or via the command line switch):

java -cp target/my-app-1.0-SNAPSHOT.jar:/.../.m2/.../new-dependency.jar com.mycompany.app.App

This will obviously get unwieldy quickly 🙂

I suspect that this is not the usual way of running a java program and that I just need to read more about .jar files, but while I am doing so I would appreciate any tips on how to do this properly.

I am not using an IDE, btw. vim from the command line.

Thanks!

Mike.

Answer 1

You can make a jar executable by adding the Main-Class attribute to its manifest file. In Maven this is done by the archiver plugin. To add the Main-Class attribute, add this to your pom.xml:

 <build>
   <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-jar-plugin</artifactId>        
      <configuration>
        <archive>
          <manifest>
            <addClasspath>true</addClasspath>
            <mainClass>com.mycompany.app.App</mainClass>
          </manifest>
        </archive>
      </configuration>
    </plugin>
  </plugins>
 </build>

You can now run your jar with the command: java -jar myjar.jar or by double clicking on it (not available in all platforms).