How to Build a Simple Jenkins‑Maven‑Git CI/CD Pipeline for Java Apps

Prerequisites

Three servers are required: a GitLab server (192.168.40.99, 8C8G, gitlab), a Jenkins server (192.168.40.98, 4C4G, jenkins/jdk/maven/git) and a test server (192.168.40.97, 2C2G, jdk).

1. GitLab Project Setup

Create a group in GitLab → Your work / Groups / New group.

Create a new blank project → New project → enter project name and click Create project.

Generate a personal access token (Preferences → Access Tokens) and copy the token value.

2. IDE Project Setup

In IntelliJ IDEA create a new Spring Web project.

Change the server port in application.properties to server.port=8088.

Add a simple @RestController that returns Hello dev.

@RestController
@RequestMapping("/")
public class HelloController {
    @RequestMapping
    public String sayHello() {
        return "Hello dev";
    }
}

3. Git Configuration in IDEA

Open Settings > Git and set the path to the local Git executable.

Initialize a Git repository, add files and commit.

Add the remote GitLab URL and push the code.

4. Jenkins CI/CD Configuration

Install the Maven plugin (Dashboard → Manage Jenkins → Plugin Manager → Available → search "maven").

Create a new Jenkins job (Dashboard → New Item → give it a name, e.g., first).

Configure the job:

Source Code Management: Git → set repository URL and credentials (use the GitLab token).

Build Triggers: enable as needed.

Build Environment: add Maven build step with goal clean package.

Configure Maven tool location (Dashboard → Manage Jenkins → Global Tool Configuration → Maven → set installation path).

5. Post‑Build Actions – Deploy JAR

Install the SSH Publisher plugin.

Add the test server under Manage Jenkins > Configure System > SSH remote hosts (host, credentials, remote directory).

In the job configuration, add a Post-build Action → Send files or execute commands over SSH.

Source files: **/target/*.jar.

Remove prefix: /target (so the JAR is placed directly in the remote directory).

Exec command:

nohup java -jar /root/jenkins-study/jenkins*.jar >> /root/jenkins-study/log.out 2>&1 &

.

6. Pre‑Build Cleanup Script

Create clean.sh on the test server ( /root) with the following content:

#!/bin/bash
appname=$1
if [ -z $appname ]; then
    echo "Application name cannot be empty!"
    exit -1
else
    echo "Application name is $1"
fi
# Remove old JARs
rm -rf $appname/${appname}*.jar
# Find running PID
pid=$(ps -ef | grep $1 | grep 'java -jar' | awk '{print $2}')
if [ -z $pid ]; then
    echo "$appname is not started"
else
    kill -9 $pid
    echo "$appname was stopped"
fi

Make it executable ( chmod 777 clean.sh) and add it as a Pre Steps command in the Jenkins job (e.g., sh ./clean.sh jenkins-study).

7. Verify Deployment

After a build, the JAR is transferred to /root on the test server.

Run jps to see the new process PID.

Access the application in a browser at http://192.168.40.97:8088 to confirm it returns the expected response.

Conclusion

The guide demonstrates a complete Jenkins CI/CD pipeline that pulls code from GitLab, builds a Spring Boot JAR with Maven, cleans up previous deployments, and deploys the new JAR to a test server using SSH, providing a foundation for further automation and scaling.