A simple, minimal Maven example: hello world

To create the files in this git repo we've already run mvn archetype:generate from http://maven.apache.org/guides/getting-started/maven-in-five-minutes.html

mvn archetype:generate -DgroupId=com.myapp.app -DartifactId=myapp -DarchetypeArtifactId=maven-archetype-quickstart -DarchetypeVersion=1.4 -DinteractiveMode=false

Now, to print "Hello World!", type either...

cd myapp
mvn compile
java -cp target/classes com.myapp.app.App

or...

cd myapp
mvn package
java -cp target/myapp-1.0-SNAPSHOT.jar com.myapp.app.App

Running mvn clean will get us back to only the source Java and the pom.xml:

murphy:myapp pdurbin$ mvn clean --quiet
murphy:myapp pdurbin$ ack -a -f
pom.xml
src/main/java/com/myapp/app/App.java
src/test/java/com/myapp/app/AppTest.java

Running mvn compile produces a class file:

murphy:myapp pdurbin$ mvn compile --quiet
murphy:myapp pdurbin$ ack -a -f
pom.xml
src/main/java/com/myapp/app/App.java
src/test/java/com/myapp/app/AppTest.java
target/classes/com/myapp/app/App.class
murphy:myapp pdurbin$ 
murphy:myapp pdurbin$ java -cp target/classes com.myapp.app.App
Hello World!

Running mvn package does a compile and creates the target directory, including a jar:

murphy:myapp pdurbin$ mvn clean --quiet
murphy:myapp pdurbin$ mvn package > /dev/null
murphy:myapp pdurbin$ ack -a -f
pom.xml
src/main/java/com/myapp/app/App.java
src/test/java/com/myapp/app/AppTest.java
target/classes/com/myapp/app/App.class
target/maven-archiver/pom.properties
target/myapp-1.0-SNAPSHOT.jar
target/surefire-reports/com.myapp.app.AppTest.txt
target/surefire-reports/TEST-com.myapp.app.AppTest.xml
target/test-classes/com/myapp/app/AppTest.class
murphy:myapp pdurbin$ 
murphy:myapp pdurbin$ java -cp target/myapp-1.0-SNAPSHOT.jar com.myapp.app.App
Hello World!

Running mvn clean compile exec:java requires https://www.mojohaus.org/exec-maven-plugin/

Running java -jar target/myapp-1.0-SNAPSHOT.jar requires http://maven.apache.org/plugins/maven-shade-plugin/

Runnable Jar:

JAR Plugin The Maven’s jar plugin will create jar file and we need to define the main class that will get executed when we run the jar file.

<plugin>
  <artifactId>maven-jar-plugin</artifactId>
  <version>3.0.2</version>
  <configuration>
    <archive>
      <manifest>
        <addClasspath>true</addClasspath>
        <mainClass>com.myapp.App</mainClass>
      </manifest>
    </archive>
  </configuration>
</plugin>

Folder tree before package:

├── pom.xml
└── src
    ├── main
    │   └── java
    │       └── com
    │           └── myapp
    │               └── app
    │                   └── App.java
    └── test
        └── java
            └── com
                └── myapp
                    └── app
                        └── AppTest.java

Folder tree after package:

.
├── pom.xml
├── src
│   ├── main
│   │   └── java
│   │       └── com
│   │           └── myapp
│   │               └── app
│   │                   └── App.java
│   └── test
│       └── java
│           └── com
│               └── myapp
│                   └── app
│                       └── AppTest.java
└── target
    ├── classes
    │   └── com
    │       └── myapp
    │           └── app
    │               └── App.class
    ├── generated-sources
    │   └── annotations
    ├── generated-test-sources
    │   └── test-annotations
    ├── maven-archiver
    │   └── pom.properties
    ├── maven-status
    │   └── maven-compiler-plugin
    │       ├── compile
    │       │   └── default-compile
    │       │       ├── createdFiles.lst
    │       │       └── inputFiles.lst
    │       └── testCompile
    │           └── default-testCompile
    │               ├── createdFiles.lst
    │               └── inputFiles.lst
    ├── myapp-1.0-SNAPSHOT.jar
    ├── surefire-reports
    │   ├── com.myapp.app.AppTest.txt
    │   └── TEST-com.myapp.app.AppTest.xml
    └── test-classes
        └── com
            └── myapp
                └── app
                    └── AppTest.class