Maven Tutorial for Beginners in 5 Steps


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Defining what Maven does is very difficult.

Every Day Developer does a lot of things

  • Manages Dependencies
    • Web Layer (Spring MVC)
    • Data Layer (JPA - Hibernate) etc..
  • Build a jar or a war or an ear
  • Run the application locally
    • Tomcat or Jetty
  • Deploy to a T environment
  • Add new dependencies to a project
  • Run Unit Tests
  • Generate Projects
  • Create Eclipse Workspace

Maven helps us do all these and more…

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Getting Started

  • Git Repository - https://github.com/in28minutes/getting-started-in-5-steps/tree/master/maven-in-5-steps
  • Pre-requisites
    • Java & Eclipse - https://www.youtube.com/playlist?list=PLBBog2r6uMCSmMVTW_QmDLyASBvovyAO3
  • We will use embedded maven in Eclipse

Overview

  • Step 1 : Creating and importing a Maven Project
  • Step 2 : Understanding Project Object Model - pom.xml
  • Step 3 : Maven Build Life Cycle
  • Step 4 : How does Maven Work?
  • Step 5 : Important Maven Commands

Step 1 : Creating and importing a Maven Project

Creating a Spring Project with Spring Initializr is a cake walk.

Spring Initializr http://start.spring.io/ is great tool to bootstrap your Spring Boot projects.

Image

As shown in the image above, following steps have to be done

  • Launch Spring Initializr and choose the following
    • Choose com.in28minutes.learning.maven as Group
    • Choose maven-in-few-steps as Artifact
    • Choose Dependency
      • Web
  • Click Generate Project.
  • Import the project into Eclipse.
  • If you want to understand all the files that are part of this project, you can go here.

Step 2 : Understanding Project Object Model - pom.xml

Naming a project

How can other projects use our project? By using our project groupId and artifactId

	<groupId>com.in28minutes.learning.maven</groupId>
	<artifactId>maven-in-few-steps</artifactId>

Parent Pom

Similar to Java Inheritance. We inherit a lot of things from starter parent.

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.0.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

Declaring Dependencies

Dependencies are frameworks that you would need to develop your project.

In the example below we are adding two dependencies.

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-test</artifactId>
	<scope>test</scope>
</dependency>

Step 3 : Maven Build Life Cycle

When we run “mvn clean install”, we are executing the complete maven build life cycle.

Build LifeCycle is a sequence of steps

  • Validate
  • Compile
  • Test
  • Package
  • Integration Test
  • Verify
  • Install
  • Deploy

Maven follows Convention over Configuration.

Pre defined folder structure

  • Source Code
    • ${basedir}/src/main/java
    • ${basedir}/src/main/resources
  • Test Code
    • ${basedir}/src/test

Step 4 : How does Maven Work?

Maven Repository contains all the jars indexed by artifact id and group id.

Once we add a dependency to our pom.xml, maven asks the maven repository for the jar dependencies giving group id and the artifact id as the input.

  • Maven repository stores all the versions of all dependencies. JUnit 4.2,4.3,4.4

The jar dependencies are stored on your machine in a folder called maven local repository. All our projects would refer to the jars from the maven local repository.

Local Repository : a temp folder on your machine where maven stores the jar and dependency files that are downloaded from Maven Repository.

Step 5 : Important Maven Commands

  • mvn –version
  • mvn compile (compiles source files)
  • mvn test-compile (compiles test files) - one thing to observe is this also compiles source files
  • mvn clean - deletes target directory
  • mvn test - run unit tests
  • mvn package - creates the jar
  • help:effective-settings
  • help:effective-pom
  • dependency:tree
  • dependency:sources
  • –debug

Complete Code Example

/pom.xml

<?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>com.in28minutes.learning.maven</groupId>
	<artifactId>maven-in-few-steps</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	
	<packaging>jar</packaging>

	<name>maven-in-few-steps</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.0.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

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

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
<!--

Remote Maven Repository
-> 
Local Maven Repository
  
 - Local Repository => Local System

 - Remote Maven repository => Central Repositories
   - stores all the versions of all dependencies. JUnit 4.2,4.3,4.4

 - mvn install vs mvn deploy 
   - copies the created jar to local maven repository - a temp folder on my machine where maven stores the files.
-->
	<repositories>
		<repository>
			<id>spring-snapshots</id>
			<name>Spring Snapshots</name>
			<url>https://repo.spring.io/snapshot</url>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
		</repository>
		<repository>
			<id>spring-milestones</id>
			<name>Spring Milestones</name>
			<url>https://repo.spring.io/milestone</url>
			<snapshots>
				<enabled>false</enabled>
			</snapshots>
		</repository>
	</repositories>

	<pluginRepositories>
		<pluginRepository>
			<id>spring-snapshots</id>
			<name>Spring Snapshots</name>
			<url>https://repo.spring.io/snapshot</url>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
		</pluginRepository>
		<pluginRepository>
			<id>spring-milestones</id>
			<name>Spring Milestones</name>
			<url>https://repo.spring.io/milestone</url>
			<snapshots>
				<enabled>false</enabled>
			</snapshots>
		</pluginRepository>
	</pluginRepositories>


</project>

/src/main/java/com/in28minutes/learning/maven/maveninfewsteps/MavenInFewStepsApplication.java

package com.in28minutes.learning.maven.maveninfewsteps;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MavenInFewStepsApplication {

	public static void main(String[] args) {
		SpringApplication.run(MavenInFewStepsApplication.class, args);
	}
}

/src/main/resources/application.properties


/src/test/java/com/in28minutes/learning/maven/maveninfewsteps/MavenInFewStepsApplicationTests.java

package com.in28minutes.learning.maven.maveninfewsteps;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class MavenInFewStepsApplicationTests {

	@Test
	public void contextLoads() {
	}

}

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