Hands-on Maven-01: Using Maven As a Build Tool

The purpose of this hands-on training is to teach the students how to use Maven with Java as a build tool.

Learning Outcomes

At the end of this hands-on training, students will be able to;

• install Maven and Java-11 on Amazon Linux EC2 instance

• explain various build phases of a Java Application

• use Maven's clean, compile, package, install, and site commands

Outline

• Part 1 - Launch Amazon Linux EC2 Instance with Cloudformation Template

• Part 2 - Generate a Java application using Maven's Archetype Plugin

• Part 3 - Run Maven Commands

Part 1 - Launch Amazon Linux EC2 Instance and Connect with SSH

• Launch an EC2 instance using maven-java-template.yml file located in this folder.

  • This template will create an EC2 instance with Java-11 and Maven.

• Connect to your instance with SSH.

• Check if you can see the Maven's binary directory under /home/ec2-user/.

• Run the command below to check if Java is available.

java -version

• Cat ~/.bash_profile file to check if Maven's path is correctly transferred. If not paste the necessary lines manually.

# Append the lines below into ~/.bash_profile file by making necessary changes.
M2_HOME=/home/ec2-user/<apache-maven-directory-with-its-version>
export PATH=$PATH:$M2_HOME/bin

• Run the command below to check if mvn commands are available.

mvn --version

• If not, run the command below and wait for the EC2 machine to get ready.

sudo reboot

Part 2 - Generate a Java application using Maven's Archetype Plugin

• Run the command below to produce an outline of a Java project with Maven.

mvn archetype:generate -DgroupId=com.clarus.maven -DartifactId=maven-experiment -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

• Cd into the project folder.

• Run the command below to be able to use the tree command.

sudo dnf install -y tree

• Run the command below to show the directory structure of the project.

tree

• Go into the folder where App.java resides and cat the auto-generated hello world application in Java.

• Replace the content of the App.java file with the content of the App.java file in this repo.

• Go into the project's root folder.

• Replace the content of the pom.xml file with the content of the pom.xml file in this repo.

• Explain that dependencyManagement section in the pom file will import multiple dependencies with compatible versions.

Part 3 - Run Maven Commands

mvn compile

 

• Run the command below.

mvn compile

• Go into the folder <project-root>/target/classes/ and show the class file.

• Run the command below to show how to test a Maven project.

mvn clean test

mvn clean test

• Show that there is a new folder named target in the project root.

• inspect the target folder with the tree command.

• Show the content of the file <project-root>/target/surefire-report/com.clarus.maven.AppTest.txt as the output of the test.

mvn package

• Run the command below.

mvn clean package

• Go into the folder <project-root>/target/ and show the maven-experiment-1.0-SNAPSHOT.jar file as the output of the mvn package command.

• Run the command below to start the application.

java -jar maven-experiment-1.0-SNAPSHOT.jar

• Explain the error in the standard output.

  • Maven's jar file is not executable. The jar file does not have either the Main Classor the necessary packages to run the application.

• Add the plugin below to the pom file and run mvn clean package command again.

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-assembly-plugin</artifactId>
      <executions>
          <execution>
              <phase>package</phase>
              <goals>
                  <goal>single</goal>
              </goals>
              <configuration>
                  <archive>
                  <manifest>
                      <mainClass>
                          com.clarus.maven.App
                      </mainClass>
                  </manifest>
                  </archive>
                  <descriptorRefs>
                      <descriptorRef>jar-with-dependencies</descriptorRef>
                  </descriptorRefs>
              </configuration>
          </execution>
      </executions>
    </plugin>
  </plugins>
</build>

mvn clean package

Run The Application

• Now, open up a fresh terminal on your local computer and run the command below.

scp -i <path-to-your-pem-file> -r <path-to-your-home-directory>/.aws ec2-user@<IP-of-your-instance>:/home/ec2-user/

• Check if the credentials are transferred to the EC2 instance.

• Go into your target folder.

• Run the command below to start the application. This time we are running the executable jar file with the suffix jar-with-dependencies.

java -jar maven-experiment-1.0-SNAPSHOT-jar-with-dependencies.jar

• Explain what the application does in the background.
  • Note that to be able to see the object and the S3 bucket, we should comment the lines 142 and 150.

mvn install

• Run the command below to install our own package into .m2 folder.

mvn install

• Go into ~/.m2/repository folder and show where our package is installed.

mvn site

• Run the command below.

mvn clean site

• Show the output site directory under the target directory.

• Run the command below to install Apache Server.

sudo dnf install -y httpd
sudo systemctl start httpd
sudo systemctl enable httpd

• Run the command below to copy the contents of the site folder under /var/www/html folder.

sudo cp -a site/. /var/www/html

• You can also use Python httpserver module:

python -m SimpleHTTPServer # for python 2.7
python3 -m http.server # for python 3+

• Go to http:// on browser to check project site.

Multi-stage builds with maven (Optional)

• Install docker

sudo dnf update -y
sudo dnf install docker -y
sudo systemctl start docker
sudo systemctl enable docker
sudo systemctl status docker
sudo usermod -a -G docker ec2-user
newgrp docker

• Create a folder named docker.

mkdir docker && cd docker

• Create a maven project.

mvn archetype:generate -DgroupId=com.clarus.maven -DartifactId=myproject -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

• Add the maven-assembly-plugin to the pom file to run the application.

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-assembly-plugin</artifactId>
      <executions>
          <execution>
              <phase>package</phase>
              <goals>
                  <goal>single</goal>
              </goals>
              <configuration>
                  <archive>
                  <manifest>
                      <mainClass>
                          com.clarus.maven.App
                      </mainClass>
                  </manifest>
                  </archive>
                  <descriptorRefs>
                      <descriptorRef>jar-with-dependencies</descriptorRef>
                  </descriptorRefs>
              </configuration>
          </execution>
      </executions>
    </plugin>
  </plugins>
</build>

• Create a multi-stage Dockerfile.

FROM maven:3.9.4-eclipse-temurin-8-alpine AS builder
COPY /myproject /app
WORKDIR /app
RUN mvn clean package

FROM openjdk:11-jre-slim
COPY --from=builder /app/target/myproject-1.0-SNAPSHOT-jar-with-dependencies.jar /app/app.jar
WORKDIR /app
CMD ["java","-jar","app.jar"]

• Build the image.

docker build -t maven-project .

• Run the container.

docker run maven-project