Javamon is a lightweight JVM monitoring agent. It can be used as a Java library or a wrapper (launcher). In the latter case there is no need to modify or recompile the target Java application source code. Javamon exposes an HTTP endpoint compatible with Prometheus, an open source monitoring system. The reference implementation has the following metrics:

More metrics can be added. For example, the source code shows how to include the active user threads count.

Adding the javamon endpoint to Prometheus (prometheus.yml):

scrape-configs:
  - job_name: 'javamon'

    # Change the target IP and port according to the javamon configuration
    static_configs:
      - targets: ['127.0.0.1:9091']

A sample Grafana dashboard is available:

Every monitoring solution introduces some overhead in terms of memory, CPU and other system resources. Javamon pretends to be as lightweight as possible while relying on standard Java features only. Javamon is implemented as a single class file, without any external dependencies. The jar file size is less than 3.5Kb. Javamon creates only one thread. It doesn't impact Garbage Collection (GC) activity.

If javamon is used as a wrapper (or launcher), there is no need to modify or recompile the source code of the target Java application. For example, let's suppose the Java application is launched as follows:

java -cp app.jar com.package.myapp var1 var2

Let's include javamon as a wrapper:

java -Djm.main=com.package.myapp -cp app.jar:javamon.jar com.agent.javamon var1 var2

Note: When using Windows, the classpath separator is ; instead of :.

The following configuration parameters are supported by the javamon wrapper:

For security reasons, the default javamon host is not 0.0.0.0, but 127.0.0.1. Therefore, if the jm.host configuration parameter is missing or empty, the HTTP endpoint will be bound to localhost. This means that by default it will be accessible only if Prometheus is running on the same host.

Please, check the javamon javadoc.

The following sample shows how to use javamon as a library (API):

import com.agent.javamon;

public class MyTestClass{
   public static void main(String[] args){
      javamon jm = new javamon("127.0.0.1", 9091);
      jm.start(); // launch the endpoint: http://127.0.0.1:9091/metrics
      // The main loop...
      jm.shut(); // signal the endpoint to stop gracefully before exiting
   }
}

A more complete example using javamon as a wrapper is available here.