如何监控jar文件变更并自动重启？含app.jar替换重启场景

Hey there! Let's figure out how to get your Java app to auto-restart whenever you replace or update app.jar. I've got a couple of solid methods for you, depending on what your server setup looks like:

Method 1: Shell Script + inotifywait (Lightweight & Flexible) #

This is a straightforward approach that uses file system event monitoring to trigger restarts. First, you'll need inotify-tools installed—it lets you track changes to files in real-time.

Install it on Debian/Ubuntu:

sudo apt update && sudo apt install inotify-tools

Or on RHEL/CentOS:

sudo yum install inotify-tools

Next, create a monitoring script (name it app_monitor.sh):

#!/bin/bash
APP_JAR="/path/to/your/app.jar"
PID_FILE="/tmp/app.pid"

# Start the application
start_app() {
    echo "Booting up app.jar..."
    nohup java -jar "$APP_JAR" > app.log 2>&1 &
    echo $! > "$PID_FILE"
    echo "App started with PID $(cat $PID_FILE)"
}

# Stop the application gracefully
stop_app() {
    if [ -f "$PID_FILE" ]; then
        PID=$(cat "$PID_FILE")
        echo "Shutting down app with PID $PID..."
        kill $PID
        rm "$PID_FILE"
        sleep 2  # Give it a moment to exit completely
    fi
}

# Launch the app initially
start_app

# Monitor for changes to app.jar
echo "Watching $APP_JAR for updates..."
while true; do
    # Trigger on file modifications, saves, or moves (like replacing the jar)
    inotifywait -e modify,close_write,moved_to "$APP_JAR"
    echo "Detected change in app.jar—restarting..."
    stop_app
    start_app
done

Make the script executable:

chmod +x app_monitor.sh

Run it in the background so it keeps working even after you log out:

nohup ./app_monitor.sh > monitor.log 2>&1 &

Pro tip: When replacing app.jar, use an atomic move to avoid partial file writes triggering false restarts:

# Upload your new jar as app.jar.tmp first, then:
mv app.jar.tmp app.jar

Method 2: Systemd Service (For Modern Linux Distros) #

If your server uses systemd (most distros like Ubuntu 16.04+, CentOS 7+), this is the cleanest, most integrated approach. Systemd handles process management and file monitoring natively.

Create a systemd service file at /etc/systemd/system/app.service:

[Unit]
Description=My Java Application
After=network.target

[Service]
Type=simple
ExecStart=/usr/bin/java -jar /path/to/your/app.jar
Restart=always
# Auto-restart when app.jar changes
PathChanged=/path/to/your/app.jar
User=your_username  # Replace with the user that should run the app
WorkingDirectory=/path/to/your/app_dir  # Optional: set the app's working directory

[Install]
WantedBy=multi-user.target

Reload systemd to recognize the new service:

sudo systemctl daemon-reload

Enable the service to start on boot:

sudo systemctl enable app.service

Start the service:

sudo systemctl start app.service

Now whenever you update or replace app.jar, systemd will automatically restart the service. You can check its status anytime with:

sudo systemctl status app.service

Method 3: Supervisor (Advanced Process Management) #

If you're already using Supervisor to manage server processes, you can pair it with inotifywait to trigger restarts on file changes.

First, install Supervisor (if not already set up):

# Debian/Ubuntu
sudo apt install supervisor
# RHEL/CentOS
sudo yum install supervisor

Create a Supervisor config for your app at /etc/supervisor/conf.d/app.conf:

[program:my_app]
command=/usr/bin/java -jar /path/to/your/app.jar
directory=/path/to/your/app_dir
user=your_username
autostart=true
autorestart=true
stdout_logfile=/var/log/app_stdout.log
stderr_logfile=/var/log/app_stderr.log

Reload Supervisor to apply the config:

sudo supervisorctl reread
sudo supervisorctl update
sudo supervisorctl start my_app

Modify the monitoring script from Method 1 to use Supervisor's restart command instead of manual PID management:

#!/bin/bash
APP_JAR="/path/to/your/app.jar"

# Restart via Supervisor
restart_app() {
    echo "Restarting app through Supervisor..."
    sudo supervisorctl restart my_app
}

echo "Watching $APP_JAR for updates..."
while true; do
    inotifywait -e modify,close_write,moved_to "$APP_JAR"
    echo "Detected change in app.jar—restarting..."
    restart_app
done

Make it executable and run it in the background just like before.

内容的提问来源于stack exchange，提问作者lessisawesome