DevopsPilot

What is Maven?

Maven is a build automation and project management tool used primarily in Java projects.

Here are some reasons why Maven is widely used:

Build Automation: Maven automates the build process, including compiling code, running tests, packaging the application (e.g., creating JAR/WAR files), and generating reports. This reduces manual work and the likelihood of errors.

Dependency Management: Maven automatically downloads and links libraries and dependencies required for your project. This ensures that all the necessary dependencies are available and correctly versioned, making it easier to manage complex projects.

Standardized Project Structure: Maven enforces a standard directory layout and build process. This consistency makes it easier to understand and navigate projects, especially when working in teams.

Reference: click here

Why do you need Maven?

The main purpose of Maven is to build automation and dependency management

When you start working on the Java project, initially you will create 1 or 2 files, compiling those Java files and running the Java program should be fine.

But when your project grows, you will start creating multiple Java files (E.g. 50 Java files), then compiling each Java file will be a boring task. To automate this build process maven is used effectively

After compiling, using Maven you can easily run the unit test case and package them as (jar, war) for deployment

During compilation, your project might depend on external libraries (dependencies), this can be easily defined in pom.xml and automatically downloaded and linked by Maven.

Java Program without Maven

1. Create a sample Calculator.java file

This Java code has methods(add, subtract) to do the addition and subtraction of two numbers defined in the variables num1, and num2 and finally print the output.

public class Calculator {
    // Method to add two numbers
    public double add(double num1, double num2) {
        return num1 + num2;
    }

    // Method to subtract two numbers
    public double subtract(double num1, double num2) {
        return num1 - num2;
    }

    public static void main(String[] args) {
        Calculator calculator = new Calculator();

        double num1 = 3;
        double num2 = 2;

        System.out.println("Sum: " + calculator.add(num1, num2));
        System.out.println("Difference: " + calculator.subtract(num1, num2));
    }
}

2. Run the ll command to check Calculator.java file is created

ll

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu  598 Aug 12 13:14 Calculator.java

3. Compile the Java file Calculator.java

Run the javac command followed by file name to compile the Java file. E.g. javac Calculator.java

javac Calculator.java

Once the compilation finishes, it will create a HelloWorld.class file

 4. Run the ll command to check the created Calculator.class file

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu 1086 Aug 12 13:20 Calculator.class
-rw-rw-r-- 1 ubuntu ubuntu  598 Aug 12 13:14 Calculator.java

5. Run the Calculator Java program

Type the java command following the Filename without extension to run the Java program E.g. java Calculator

java Calculator

Output:

ubuntu@vignesh-jenkins2:~/java$ java Calculator
Sum: 5.0
Difference: 1.0

6. Create a Unit Test Java file for the Calculator Program

Unit test is a process to test the method or small unit in a program.

In the above program, you have 2 methods add and subtract. Unit test is used to test whether these 2 methods will give a correct output when you give different inputs (scenarios).

JUnit is a widely used unit testing framework for Java programming language

Create a file CalculatorTest.java

import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class CalculatorTest {

    @Test
    public void testAdd() {
        Calculator calculator = new Calculator();
        double result = calculator.add(10, 5);
        assertEquals(15, result, 0);
    }

    @Test
    public void testSubtract() {
        Calculator calculator = new Calculator();
        double result = calculator.subtract(10, 5);
        assertEquals(5, result, 0);
    }
}

The above Java file will refer to the Calculator Java file and call the add method by passing two numbers (10, 5), expecting the result to be 15. If the add method returns 15, then this test case is a pass.

Similarly, it calls the subtract method by passing two numbers (10, 5), expecting the result to be 5. If the subtract method returns 5, then the test case is a pass else fail.

It uses the JUnit assertEquals methods to check whether the output is Equal to your expected value or not.

7. Run the ll command to check CalculatorTest.java file is created

ll

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu 1086 Aug 12 13:20 Calculator.class
-rw-rw-r-- 1 ubuntu ubuntu  598 Aug 12 13:14 Calculator.java
-rw-rw-r-- 1 ubuntu ubuntu  468 Aug 12 13:47 CalculatorTest.java

8. Compile the Test Java file CalculatorTest.java

Run the following command to compile the CalculatorTest.java

javac CalculatorTest.java

Output:

ubuntu@vignesh-jenkins2:~/java$ javac CalculatorTest.java
CalculatorTest.java:1: error: package org.junit does not exist
import org.junit.Test;
                ^
CalculatorTest.java:2: error: package org.junit does not exist
import static org.junit.Assert.assertEquals;
                       ^
CalculatorTest.java:2: error: static import only from classes and interfaces
import static org.junit.Assert.assertEquals;
^
CalculatorTest.java:6: error: cannot find symbol
    @Test
     ^
  symbol:   class Test
  location: class CalculatorTest
CalculatorTest.java:13: error: cannot find symbol
    @Test
     ^
  symbol:   class Test
  location: class CalculatorTest
CalculatorTest.java:10: error: cannot find symbol
        assertEquals(15, result, 0);
        ^
  symbol:   method assertEquals(int,double,int)
  location: class CalculatorTest
CalculatorTest.java:17: error: cannot find symbol
        assertEquals(5, result, 0);
        ^
  symbol:   method assertEquals(int,double,int)
  location: class CalculatorTest
7 errors

Compilation fails since it depends on the junit Java library

9. Download the Junit library file

In Java library files are available in the .jar extension.

Run the following command to download the 2 jar files. junit library depends on the hamcrest-core library. This is called transitive dependency

wget https://repo1.maven.org/maven2/junit/junit/4.13.2/junit-4.13.2.jar
wget https://repo1.maven.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar

Output:

ubuntu@vignesh-jenkins2:~/java$ wget https://repo1.maven.org/maven2/junit/junit/4.13.2/junit-4.13.2.jar
--2024-08-12 14:22:37--  https://repo1.maven.org/maven2/junit/junit/4.13.2/junit-4.13.2.jar
Resolving repo1.maven.org (repo1.maven.org)... 151.101.40.209, 2a04:4e42:a::209
Connecting to repo1.maven.org (repo1.maven.org)|151.101.40.209|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 384581 (376K) [application/java-archive]
Saving to: ‘junit-4.13.2.jar’

junit-4.13.2.jar                    100%[================================================================>] 375.57K   417KB/s    in 0.9s    

2024-08-12 14:22:38 (417 KB/s) - ‘junit-4.13.2.jar’ saved [384581/384581]
ubuntu@vignesh-jenkins2:~/java$ wget https://repo1.maven.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar
--2024-08-12 14:22:44--  https://repo1.maven.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar
Resolving repo1.maven.org (repo1.maven.org)... 151.101.40.209, 2a04:4e42:a::209
Connecting to repo1.maven.org (repo1.maven.org)|151.101.40.209|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 45024 (44K) [application/java-archive]
Saving to: ‘hamcrest-core-1.3.jar’

hamcrest-core-1.3.jar               100%[================================================================>]  43.97K   177KB/s    in 0.2s    

2024-08-12 14:22:46 (177 KB/s) - ‘hamcrest-core-1.3.jar’ saved [45024/45024]

 10. Run the ll command to see the downloaded files

ll

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu   1086 Aug 12 13:20 Calculator.class
-rw-rw-r-- 1 ubuntu ubuntu    598 Aug 12 13:14 Calculator.java
-rw-rw-r-- 1 ubuntu ubuntu    468 Aug 12 13:47 CalculatorTest.java
-rw-rw-r-- 1 ubuntu ubuntu  45024 Jul  9  2012 hamcrest-core-1.3.jar
-rw-rw-r-- 1 ubuntu ubuntu 384581 Feb 13  2021 junit-4.13.2.jar

11 Compile the Test Java file CalculatorTest.java

You need to pass the jar files as parameters to the javac command to refer to the jar files during compilation

Run the following command to compile

javac -cp .:junit-4.13.2.jar:hamcrest-core-1.3.jar CalculatorTest.java

Once the compilation finishes, it will create a CalculatorTest.class file

 12. Run the ll command to check the created CalculatorTest.class file

ll

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu   1086 Aug 12 13:20 Calculator.class
-rw-rw-r-- 1 ubuntu ubuntu    598 Aug 12 13:14 Calculator.java
-rw-rw-r-- 1 ubuntu ubuntu    603 Aug 12 14:29 CalculatorTest.class
-rw-rw-r-- 1 ubuntu ubuntu    468 Aug 12 13:47 CalculatorTest.java
-rw-rw-r-- 1 ubuntu ubuntu  45024 Jul  9  2012 hamcrest-core-1.3.jar
-rw-rw-r-- 1 ubuntu ubuntu 384581 Feb 13  2021 junit-4.13.2.jar

13. Run the JUnit Test

Run the following command to run the CalculatorTest to test the program

java -cp .:junit-4.13.2.jar:hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest

Output:

ubuntu@vignesh-jenkins2:~/java$ java -cp .:junit-4.13.2.jar:hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest
JUnit version 4.13.2
..
Time: 0.018

OK (2 tests)

Both the test cases are passed.

You can see the difficulties in maintaining the dependencies. For a big project, there could be hundreds of dependencies, with Maven this can be easily managed.

14. Cleanup the compiled class files and downloaded jar files

Run the following command to delete the Calculator.class, CalculatorTest.class, junit-4.13.2.jar and hamcrest-core-1.3.jar

rm -f *.class *.jar

Verify the files are deleted

ll

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu  598 Aug 12 13:14 Calculator.java
-rw-rw-r-- 1 ubuntu ubuntu  468 Aug 12 13:47 CalculatorTest.java

Java Program with Maven

Maven expects the Java files to be in a proper folder structure with pox.xml in the root folder like this

├── pom.xml
└── src
    ├── main
    │   └── java
    │       └── Calculator.java
    └── test
        └── java
            └── CalculatorTest.java

1. Create src/main/java folder and move Calculator.java into it

All development Java files are kept inside the src/main/java folder as per the Maven folder structure

Run the following command to create the src/main/java folder

mkdir -p src/main/java

Check folder is created

ll
tree

Output:

ubuntu@vignesh-jenkins2:~/java$ ll
-rw-rw-r-- 1 ubuntu ubuntu  598 Aug 12 13:14 Calculator.java
-rw-rw-r-- 1 ubuntu ubuntu  468 Aug 12 13:47 CalculatorTest.java
drwxrwxr-x 3 ubuntu ubuntu 4096 Aug 13 14:26 src/
ubuntu@vignesh-jenkins2:~/java$ tree
├── Calculator.java
├── CalculatorTest.java
└── src
    └── main
        └── java

Run the following command to move the Calculator.java into src/main/java folder

mv Calculator.java src/main/java

Verify Calculator.java file moved into src/main/java

tree

Output:

ubuntu@vignesh-jenkins2:~/java$ tree
├── CalculatorTest.java
└── src
    └── main
        └── java
            └── Calculator.java

2. Create src/test/java folder and move CalculatorTest.java into it

All Unit Test Java files are kept inside the src/test/java folder as per the Maven folder structure

Run the following command to create the src/test/java folder

mkdir -p src/test/java

Check folder is created

tree

Output:

ubuntu@vignesh-jenkins2:~/java$ tree
├── CalculatorTest.java
└── src
    ├── main
    │   └── java
    │       └── Calculator.java
    └── test
        └── java

Run the following command to move the CalculatorTest.java into the src/test/java folder

mv CalculatorTest.java src/test/java

Verify CalculatorTest.java file moved into src/test/java

tree

Output:

ubuntu@vignesh-jenkins2:~/java$ tree
└── src
    ├── main
    │   └── java
    │       └── Calculator.java
    └── test
        └── java
            └── CalculatorTest.java

3. Create a pom.xml file in the root folder

pom.xml file contains information about the project and configuration details used by Maven to build the project

pom.xml should be kept in the root folder

mvn command should be executed from where the pom.xml is located.

Maven identifies this as a Maven project by identifying the pom.xml file and its information

Create pox.xml file

<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>com.example</groupId>
    <artifactId>calculator-project</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
      <plugins>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.12.1</version>
        </plugin>
      </plugins>
    </build>
    <dependencies>
        <!-- JUnit dependency -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

pox.xml has important fields like groupId, artifactId, and version to track the project details

Now dependencies like JUnit can be easily defined under the dependency block in pom.xml

During compilation, it automatically downloads the jar files and keeps them inside the ~/.m2 folder

One more important thing, it automatically downloads the transitive dependency, you do not need to define it in the pom.xml

Here hamcrest-core-1.3.jar is a transitive dependency for the Junit library, Maven will automatically download it

Final folder structure

tree

Output:

ubuntu@vignesh-jenkins2:~/java$ tree
├── pom.xml
└── src
    ├── main
    │   └── java
    │       └── Calculator.java
    └── test
        └── java
            └── CalculatorTest.java

4. Compile the Java program using the Maven command

Run the following Maven command to compile the Maven project

mvn compile

Output:

ubuntu@vignesh-jenkins2:~/java$ mvn compile
[INFO] Scanning for projects...
[INFO] 
[INFO] -------------------< com.example:calculator-project >-------------------
[INFO] Building calculator-project 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-resources-plugin/2.6/maven-resources-plugin-2.6.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-resources-plugin/2.6/maven-resources-plugin-2.6.pom (8.1 kB at 5.6 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugins/23/maven-plugins-23.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugins/23/maven-plugins-23.pom (9.2 kB at 67 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/maven-parent/22/maven-parent-22.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/maven-parent/22/maven-parent-22.pom (30 kB at 189 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/apache/11/apache-11.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/apache/11/apache-11.pom (15 kB at 95 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-resources-plugin/2.6/maven-resources-plugin-2.6.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-javac/2.14.2/plexus-compiler-javac-2.14.2.jar (23 kB at 63 kB/s)
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-utils/4.0.0/plexus-utils-4.0.0.jar (192 kB at 509 kB/s)
[INFO] Recompiling the module because of changed source code.
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file with javac [debug target 1.8] to target/classes
[WARNING] bootstrap class path not set in conjunction with -source 8
[WARNING] source value 8 is obsolete and will be removed in a future release
[WARNING] target value 8 is obsolete and will be removed in a future release
[WARNING] To suppress warnings about obsolete options, use -Xlint:-options.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  16.675 s
[INFO] Finished at: 2024-08-13T15:13:55Z
[INFO] ------------------------------------------------------------------------

It creates a class file inside the target/classes folder

tree

Output:

ubuntu@vignesh-jenkins2:~/java$ tree
├── pom.xml
├── src
│   ├── main
│   │   └── java
│   │       └── Calculator.java
│   └── test
│       └── java
│           └── CalculatorTest.java
└── target
    ├── classes
    │   └── Calculator.class
    ├── generated-sources
    │   └── annotations
    └── maven-status
        └── maven-compiler-plugin
            └── compile
                └── default-compile
                    ├── createdFiles.lst
                    └── inputFiles.lst

5. Compile the Java program using the Maven command

Run the following Maven command to run the Junit test

mvn test

When you run the mvn test, it compiles first and then executes the Junit test cases.

Output:

ubuntu@vignesh-jenkins2:~/java$ mvn test
[INFO] Scanning for projects...
[INFO] 
[INFO] -------------------< com.example:calculator-project >-------------------
[INFO] Building calculator-project 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-surefire-plugin/2.12.4/maven-surefire-plugin-2.12.4.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-surefire-plugin/2.12.4/maven-surefire-plugin-2.12.4.pom (10 kB at 13 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/surefire/surefire/2.12.4/surefire-2.12.4.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/surefire/surefire/2.12.4/surefire-2.12.4.pom (14 kB at 104 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-surefire-plugin/2.12.4/maven-surefire-plugin-2.12.4.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/surefire/surefire-providers/2.12.4/surefire-providers-2.12.4.pom (2.3 kB at 20 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/surefire/surefire-junit4/2.12.4/surefire-junit4-2.12.4.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/surefire/surefire-junit4/2.12.4/surefire-junit4-2.12.4.jar (37 kB at 313 kB/s)

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running CalculatorTest
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.141 sec

Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  10.415 s
[INFO] Finished at: 2024-08-13T15:17:01Z
[INFO] ------------------------------------------------------------------------

Test class files are kept inside the target/test-classes folder

tree

Output:

ubuntu@vignesh-jenkins2:~/java$ tree
├── pom.xml
├── src
│   ├── main
│   │   └── java
│   │       └── Calculator.java
│   └── test
│       └── java
│           └── CalculatorTest.java
└── target
    ├── classes
    │   └── Calculator.class
    ├── generated-sources
    │   └── annotations
    ├── generated-test-sources
    │   └── test-annotations
    ├── maven-status
    │   └── maven-compiler-plugin
    │       ├── compile
    │       │   └── default-compile
    │       │       ├── createdFiles.lst
    │       │       └── inputFiles.lst
    │       └── testCompile
    │           └── default-testCompile
    │               ├── createdFiles.lst
    │               └── inputFiles.lst
    ├── surefire-reports
    │   ├── CalculatorTest.txt
    │   └── TEST-CalculatorTest.xml
    └── test-classes
        └── CalculatorTest.class

6. Package the program and create a Jar file

With Maven you can package your Java program/application into a JAR/WAR package

JAR can be created and used in another Java program as a library.

Similarly, WAR can be created to deploy to the Tomcat Webserver to see your application from a Browser like Chrome

Add this maven-jar-plugin plugin code under the plugins block in the pom.xml to generate a jar file

<!-- Jar plugin to specify the main class -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>3.2.0</version>
    <configuration>
        <archive>
            <manifest>
                <mainClass>Calculator</mainClass>
            </manifest>
        </archive>
    </configuration>
</plugin>

Final pom.xml after adding the maven-jar-plugin plugin

<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>com.example</groupId>
    <artifactId>calculator-project</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
      <plugins>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.12.1</version>
        </plugin>
    
        <!-- Jar plugin to specify the main class -->
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-jar-plugin</artifactId>
          <version>3.2.0</version>
          <configuration>
            <archive>
              <manifest>
                <mainClass>Calculator</mainClass>
              </manifest>
            </archive>
          </configuration>
        </plugin>    
      </plugins>
    </build>
    <dependencies>
        <!-- JUnit dependency -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

Run the following command to create a Jar package

mvn clean package

When you run the mvn clean package, it deletes the existing target folder, compiles freshly, executes the Junit test cases, and then creates the Jar file

Output:

ubuntu@vignesh-jenkins2:~/java$ mvn clean package
[INFO] Scanning for projects...
[INFO] 
[INFO] -------------------< com.example:calculator-project >-------------------
[INFO] Building calculator-project 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-jar-plugin/3.2.0/maven-jar-plugin-3.2.0.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-jar-plugin/3.2.0/maven-jar-plugin-3.2.0.pom (7.3 kB at 8.1 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugins/33/maven-plugins-33.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugins/33/maven-plugins-33.pom (11 kB at 75 kB/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-jar-plugin/3.2.0/maven-jar-plugin-3.2.0.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-jar-plugin/3.2.0/maven-jar-plugin-3.2.0.jar (29 kB at 188 kB/s)
[INFO] Building jar: /home/ubuntu/java/target/calculator-project-1.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  16.728 s
[INFO] Finished at: 2024-08-15T11:09:33Z
[INFO] ------------------------------------------------------------------------

The jar file is here target/calculator-project-1.0-SNAPSHOT.jar

7. Execute the Jar file to run the Java program

Run the following command to run the program

java -jar target/calculator-project-1.0-SNAPSHOT.jar

Output:

ubuntu@vignesh-jenkins2:~/java$ java -jar target/calculator-project-1.0-SNAPSHOT.jar
Sum: 15.0
Difference: 5.0

Maven is very useful in the CI/CD process to automate the building of application