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.
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
- Choose
- 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>2.3.1.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>2.3.1.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>
<maven-jar-plugin.version>3.1.1</maven-jar-plugin.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() {
}
}