What is pom.xml in Maven

 

✅ 1. What is pom.xml in Maven?

• pom.xml (Project Object Model) is the configuration file for Maven.

• It defines:

  • Your project details

  • Dependencies (like libraries you use)

  • Build settings

  • Plugins (extra build tools, like making fat JAR)

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✅ 2. Maven pom.xml Structure with Explanation

xml

<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.mitesh</groupId>
    <artifactId>myproject</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <!-- ✅ Dependencies: libraries your code needs -->
    <dependencies>
        <!-- Example 1: Gson -->
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.10.1</version>
        </dependency>

        <!-- Example 2: Apache Commons Lang -->
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.12.0</version>
        </dependency>
    </dependencies>

    <!-- ✅ Build section: define plugins and extra build behavior -->
    <build>
        <plugins>
            <!-- Fat JAR Plugin -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>3.3.0</version>
                <configuration>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                    <archive>
                        <manifest>
                            <mainClass>com.mitesh.MainApp</mainClass> <!-- Replace with your actual class -->
                        </manifest>
                    </archive>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

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✅ 3. What Each Section Means

Section	Purpose
<dependencies>	Libraries you need (like Gson, Spring, etc.)
<build>	Defines plugins and how to build
<plugins>	Extra build tools (e.g., for fat JAR)
<mainClass>	Entry point (the main() method class)

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✅ 4. Maven Commands

Task	Command
Clean old builds	mvn clean
Compile Java code	mvn compile
Create normal JAR	mvn package
Create fat JAR (with plugin)	mvn clean compile assembly:single

🔹 This command will generate:

target/myproject-1.0.0-jar-with-dependencies.jar

---

✅ 5. Run the Fat JAR

java -jar target/myproject-1.0.0-jar-with-dependencies.jar

This works anywhere — no need to install the 3 dependencies on target machine.

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🧪 Sample Java Class

File: src/main/java/com/mitesh/MainApp.java

package com.mitesh;

import com.google.gson.Gson;

public class MainApp {
    public static void main(String[] args) {
        Person p = new Person("Mitesh", 30);
        String json = new Gson().toJson(p);
        System.out.println("JSON = " + json);
    }
}

class Person {
    String name;
    int age;
    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}