How to create a fat jar?

Question

With SpringBoot, you have the @SpringBootApplication annotation, but what is the equivalent with the neat Java Spark framework?

IntelliJ creates a Maven project and I added the spark dependency, but running the install goal, I get a 5 KB jar with no manifest. Not an executable jar.

The pom.xml created thus far is as follows:

<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>sparkdemo</groupId>
  <artifactId>sparkdemo</artifactId>
  <version>1.0 </version>
  <packaging>jar</packaging>

  <name>sparkdemo</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>com.sparkjava</groupId>
      <artifactId>spark-core</artifactId>
      <version>2.5.4</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.3</version>
        <configuration>
          <source>${java.version}</source>
          <target>${java.version}</target>
          <optimize>true</optimize>
          <debug>true</debug>
        </configuration>
      </plugin>
    </plugins>
  </build>

</project>

Would appreciate any suggestions....Thanks!

Answer 1

What you need here is an executable jar that will not only contain your classes, but also classes from all your dependencies. For that you can use the Maven Assembly Plugin.

See the sample code below.

<project>
  [...]
  <build>
    [...]
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>3.0.0</version>
        <configuration>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
          <archive>
            <manifest>
              <mainClass>org.sample.App</mainClass>     // specify your main class here
            </manifest>
          </archive>
        </configuration>
        <executions>
          <execution>
            <id>make-assembly</id> <!-- this is used for inheritance merges -->
            <phase>package</phase> <!-- bind to the packaging phase -->
            <goals>
              <goal>single</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      [...]
</project>

Then, run mvn package and the executable jar should be located in the folder target (with a name like ProjectName-1.0-SNAPSHOT-jar-with-dependencies.jar).