如何编译基于Maven的Java项目以从命令行运行它

Question

I have a Maven project that I need somehow to compile so I'd be able to transfer the compiled file to a different machine and then execute there (with potentially different Java version). I looked at this SO question

and was able to execute:

mvn clean install
mvn dependency:copy-dependencies

Yet when I tried:

cd target/
java -cp myApp-0.0.1.jar:dependency myApp

I got

Error: Could not find or load main class myApp

My pom.xml does not have mvn-assembly-plugin or maven-jar-plugin (and I successfully get the .jar in target/ after mvn clean install).

I am not sure whether those steps are related to my goal because what I need is to create something that will run without any java -jar or mvn and could be ported and run on a different machine.

Answer 1

There is Maven build plugin that would bundle all your dependencies in a JAR. You could execute it simply with

java -jar mybundled.jar

without caring about class path dependencies.

And here comes the Maven plugin. Replace the MainClass with your entry point.

<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-assembly-plugin</artifactId>
   <version>2.4.1</version>
   <configuration>
      <descriptorRefs>
         <descriptorRef>jar-with-dependencies</descriptorRef>
      </descriptorRefs>       
      <archive>
        <manifest>
          <mainClass>com.yourdomain.Main</mainClass>
        </manifest>
      </archive>
     </configuration>
    <executions>
      <execution>
         <id>make-assembly</id>
         <phase>package</phase>
         <goals>
           <goal>single</goal>
         </goals>
       </execution>
    </executions>
</plugin>

As it is bound to the package lifecycle , you would find your bundled JAR in your target directory after doing a ...

mvn package

Regarding your concern that your code won't run on another machine, Java is platform-independent and generally you can rely on that. However, three things come to my mind that can make life hard:

1. Your code depends on the system encoding. Maven should give you a warning on that in the log, advising you to specify it explicitly.
2. You interact with the runtime, like executing system commands. ps won't work on windows and dir /s probably not on *nix.
3. The version of your Java environment differ. Of course, JavaFX code won't run with a Java 1.5. If you use the latest features, make sure your clients already have the respective version or, at least, are able to get it from somewhere. You might want to take a look at the source and target compile options, too: http://docs.oracle.com/javase/7/docs/technotes/tools/windows/javac.html#crosscomp-example