DevOps Classroom Series – 11/Jul/2021

Building Java Applications using Maven

• JDK comes with in built java compiler, which can be used to create the java compiled classes
• Build tools in Java help in building the jar/war files from the java code
• In this we would also like to run unit tests
• There was a popular tool called as Ant to perform these operations.
• In Ant we are supposed to write configuration files and in the configuration files we need to define the sequence of instructions that needs to be carried out.
• The instructions are generally written in build.xml file Refer Here for the sample
• Refer Here for the sample java project with ant
• When we write the java code, we use lot of code which is already. This is something which we call as dependency
• So now in this day , we need build tools to
  • build the java code
  • unit test the java code
  • manage the dependencies.

Maven

• Maven is a powerful build tool for Java Projects (Java Based Languages).
• Maven believes in Convention over Configuration
• Refer Here for the website of maven
• Lets use maven to build some java code
• Lab Setup
  • System 1: Create an ubuntu linux instance in any cloud/hypervisors and ensure it has internet connection
    • Install Open JDK8

    sudo apt update
    sudo apt install openjdk-8-jdk -y
    

    • JAVA is installed on the folder /usr/lib/jvm/java-8-openjdk-amd64 which is considered as JAVA HOME and we need to create an environment variable JAVA_HOME representing home directory of java

    export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
    

    • Add the JAVA_HOME to either /etc/environment or ~/.bashrc
    • Download the latest version of maven

    cd /tmp
     wget https://mirrors.estointernet.in/apache/maven/maven-3/3.8.1/binaries/apache-maven-3.8.1-bin.tar.gz
     tar -xvzf apache-maven-3.8.1-bin.tar.gz
     sudo mv apache-maven-3.8.1 /var/lib/maven-3.8.1
    

    • Now we need to create M2_HOME environment variable which point to /var/lib/maven-3.8.1 and add /var/lib/maven-3.8.1/bin to path
    • Open ~/.bashrc and add the following lines to the end of the file

    export JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64"
    export M2_HOME="/var/lib/maven-3.8.1"
    export PATH=$PATH:$JAVA_HOME/bin:$M2_HOME/bin
    

    • Now logout and login

    mvn --version
    

    • Can we install maven latest version with JDK 11
• On windows to install java and maven . First install chocolatey Refer Here

choco install jdk11 -y
choco install maven -y

• On Mac install homebrew Refer Here

  • Java Refer Here
  • maven Refer Here

• Conventions over configurations

Maven POM

• POM stands for Project Object Model.

• This is fundamental unit of work in Maven

• This contains information about the project and various configuration details used by Maven

• Goals:

  • compile: will compile the java code
  • test: will compile and run the test code
  • package: will test and create the jar/war file
  • install: will package and copy the package with pom file in local repository
  • deploy: will install and deploy the package to maven repository
  • clean : will remove the target folder

• In POM we will have the following information

  • project dependencies
  • plugins
  • goals
  • build profiles
  • project version

• Elements of POM

• The build package will have the following format

<artifactId>-<version>.<packagingformat>

• Super POM:
  • This is Maven’s default POM. All POMs inherit from this parent or default POM
  • Try executing

  mvn help:effective-pom
  

• What are Repositories in maven?
• What is Build life cycle in maven
• What are Build profiles
• What are Plugins

Jenkins contd

• From Jenkins lets build a java project and show the jar files to user

• Execute mvn package from Execute shell after configuring git repository of java project Refer Here

• Now lets explore how jenkins is storing the projects

• cd in to the home directory of jenkins (/var/lib/jenkins) as jenkins user and see the contents

• Now get into jobs/your job name

• The jenkins project created gets stored as xml file in /var/lib/jenkins/jobs/$job-name/config.xml

• Now lets cd into /var/lib/jenkins/workspace

• Now lets cd into firstbuild

• Jenkins when a project is created stores an xml file in the $JENKINS_HOME/jobs/<your-job-name>/config.xml and when the project is executed all the work is done in the workspace folder $JENKINS_HOME/workspace/<your-job-name>/