I use Apache Airflow 2.10.5 to run a task implemented in Java. This task is implemented by a PythonOperator that calls a Java method by using JPype. The Java method performs System.out.println. Unfortunately, these traces do not appear in Airflow logs (nor in the UI), although the traces from Python code do appear.

What is strange is that the expected trace from System.out.println (i.e. "INFO - Java code JPypeTest.call invoked !!!!!!") can be seen in the console of the airflow scheduler !

Does anyone have solved this kind of issue ?

Here is my DAG :

from datetime import datetime, timedelta
from airflow.models.dag import DAG
from airflow.operators.python import PythonOperator
import jpype


def test_jpype():

    print("Start JVM")
    jpype.startJVM()

    print("Load JPypeTest Java class")
    JPypeTest = jpype.JClass("JPypeTest")
    print("Instanciate JPypeTest Java class")
    jpype_test = JPypeTest()
    print("Invoke method 'call' of JPypeTest Java class")
    jpype_test.call()

    print("Shutdown JVM")
    jpype.shutdownJVM()

    print("Done.")

with DAG(
    "test_jpype",
    default_args={
        "depends_on_past": False,
        "email": ["[email protected]"],
        "email_on_failure": False,
        "email_on_retry": False,
        "retries": 0,
    },
    description="Run a task that calls Java code with JPype",
    schedule=None,
    catchup=False,
    tags=["test_jpype"],
) as dag:

    task_test_jpype = PythonOperator(
        task_id="test_jpype",
        python_callable=test_jpype,
    )

    task_test_jpype

and here is my Java class :

public class JPypeTest
{
    public synchronized void call()
    {
        System.out.println("INFO - Java code JPypeTest.call invoked !!!!!!");
        System.out.flush();
    }
}

Here are the traces found in the log file and the UI :

[2025-04-01T13:44:19.734+0200] {logging_mixin.py:190} INFO - Task instance is in running state
[2025-04-01T13:44:19.735+0200] {logging_mixin.py:190} INFO -  Previous state of the Task instance: queued
[2025-04-01T13:44:19.735+0200] {logging_mixin.py:190} INFO - Current task name:test_jpype state:running start_date:2025-04-01 11:44:19.604270+00:00
[2025-04-01T13:44:19.735+0200] {logging_mixin.py:190} INFO - Dag name:test_jpype and current dag run status:running
[2025-04-01T13:44:19.735+0200] {taskinstance.py:732} INFO - ::endgroup::
[2025-04-01T13:44:19.735+0200] {logging_mixin.py:190} INFO - Start JVM
[2025-04-01T13:44:19.983+0200] {logging_mixin.py:190} INFO - Load JPypeTest Java class
[2025-04-01T13:44:19.983+0200] {logging_mixin.py:190} INFO - Instanciate JPypeTest Java class
[2025-04-01T13:44:19.984+0200] {logging_mixin.py:190} INFO - Invoke method 'call' of JPypeTest Java class
[2025-04-01T13:44:19.984+0200] {logging_mixin.py:190} INFO - Shutdown JVM
[2025-04-01T13:44:19.993+0200] {logging_mixin.py:190} INFO - Done.
[2025-04-01T13:44:19.993+0200] {python.py:240} INFO - Done. Returned value was: None

Many thanks.