Building a simple java app with external dependencies

This blog describes, how we can build a simple java application using couple of external dependencies. This can help in decopuling certain components from a big corporate application and test it.

We will use maven to create the project and the dependency.

Create project:

Follwing official maven instructions, let’s create a project

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

Dependency

We will take dependency on couple of logging realted jars.

Write code

import lombok.extern.log4j.Log4j2;
@Log4j2
public class App 
{
    public static void main( String[] args )
    {
        System.out.println( "\nHello World!"+ log.getClass() );
        log.error("\nHello world from logger log4j");
    }
}

Add dependencies

Add the following 3 dependencies in pom.xml’s

<dependencies>
...
</dependencies>

section.

These dependencies should be provided both during compile and run time.

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.22</version>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.17.2</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.17.2</version>
</dependency>

Build and run

This shortcut command both creates and runs the final application by properly resolving dependencies.

mvn exec:java -Dexec.mainClass="com.mycompany.app.App"'

This should print couple of messages. One from System.out.println and another from log.error.

If you are using mvn package just to build and planning to run the jar after that, then make sure to provide the dependencies again while running the final jar or create a jar with dependencies in the first place.