Maven - Executable file from a java project

Question

I need to use maven (for a school project) to create an executable file from a single maven command. I've never used maven and tried many solutions here on stackoverlow. The solutions created a jar file, but the file never opened.

This is my project structure

src
    com
        project
                code
                       swing
                             programm
                                      interface
                                               Main.class

I know this isn't maven convention, however changing it now would mean I would have to adjust the imports (as intelliJ doesn't refactor everything perfectly) for around 40 classes.

<?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>MyGroup</groupId>
<artifactId>myProgramm</artifactId>
<version>0.7-SNAPSHOT</version>
<packaging>jar</packaging>
<name>Hello World</name>
<description>Course Project</description>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <java.version>1.8</java.version>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

<dependencies>
    <!-- https://mvnrepository.com/artifact/org.xerial/sqlite-jdbc -->
    <dependency>
        <groupId>org.xerial</groupId>
        <artifactId>sqlite-jdbc</artifactId>
        <version>3.25.2</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.junit/junit5-engine -->
    <dependency>
        <groupId>org.junit</groupId>
        <artifactId>junit5-engine</artifactId>
        <version>5.0.0-ALPHA</version>
    </dependency>

</dependencies>

<build>

</build>

What do I have to put inside to make an executable file?

Irrelevant

In executable you mean a platform-specific binary or a jar file, which can be executed using JVM installed on the PC? – Arnaud

"as intelliJ doesn't refactor everything perfectly" why do you say that? I've not had a problem with that...basically ever, with any IDE I've used. – Caraway

By maven default convention java sources should be placed in src/main/java – Tenement

@Arnaud by executable I mean a jar file, should have clarified that. At: VLAZ I also usually never had a problem with refactoring, however, this time it didn't work. Don't know why... – Irrelevant

Answer 1

You need to add plugin to your pom.xml file

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>1.2.1</version>
            <configuration>
                <mainClass>com.example.Main</mainClass>
            </configuration>
        </plugin>
    </plugins>
</build>

and to run the program: mvn clean install exec:java

... here is the link for doc http://www.mojohaus.org/exec-maven-plugin/usage.html

There are possible different solutions, depends on your requirements: https://www.baeldung.com/executable-jar-with-maven

Perla

I'm getting a java.lang.ClassNotFoundException. Trying to execute the file with norbert's idea, also gives me the error message that the main class couldn't be found – Irrelevant

I've seen to have found the solution. I added the <sourceDirectory></sourceDirectory> to my build. Now I'm getting new errors that do not seem related to this one. – Irrelevant

@Irrelevant You can share the error and maybe some one will help with it – Perla

Answer 2

TimurJD's answer is correct however I would like to explain step by step what is actually happening and why.

• To have a jar be executable the JVM needs to know where your main method is.

• For that you need a file called META-INF/MANIFEST.MF inside the jar you create.

• This file must contain a reference to the class containing your main method which is done like this:

   Main-Class: com.example.ClassContainingMainMethod
  

• There are many ways of creating said file but since you are using maven here is the plugin that will help you create this manifest file

  <build>
      <plugins>
          <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-jar-plugin</artifactId>
              <version>3.1.1</version>
              <configuration>
                  <archive>
                      <manifest>
                          <addClasspath>true</addClasspath>
                          <classpathPrefix>lib/</classpathPrefix>
                          <mainClass>com.my.packege.Main</mainClass>
                      </manifest>
                  </archive>
              </configuration>
          </plugin>
      </plugins>
  </build>
  

• Once you have the plugin in your pom.xml simply run the maven install goal, either from your IDE or the command line. After you should find a folder called target in your project. That folder will contain the executable jar.

• To run the jar you can call from the command line:

  java -jar MyProject.jar
  

It should also be noted that unless you abide by the maven standard of keeping your source code in src/main/java you will have to specify your source folder explicitly.

Humbertohumble