======================
Java Development Tools
======================

When developing with Java, you will want to use some tooling for deeper
analysis of failures, hot-redeploys of the application, etc.

Please step through the different tools below to learn how you can use them
when using a (local) Kubernetes deployment as a part of your development
workflow.

These functionality is only enabled in the development flavors of :doc:`/images/dataverse-k8s`.
You should not (and cannot) enable this in production.

**When using the** ``dev`` **persona (default with** ``skaffold``\ **), JMX and JDWP support**
**will be enabled for you. See below for details on how to use.**

.. seealso:: If you need to swap out your production pod, take a look at `telepresence <https://www.telepresence.io/>`_.

Metrics and Performance with VisualVM
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. note:: The below is for Glassfish based images. Payara enables
          JMX on port 8686 by default, but requires SSL handling.
          Find more details in `this Payara Blog entry <https://blog.payara.fish/monitoring-payara-server-with-jconsole>`_.
          Setting ``ENABLE_JMX=1`` has no effect.

On startup, when the environment variable ``ENABLE_JMX=1``, the application
server is configured to listen on port ``4000`` and ``4001`` for JMX & RMI traffic
from ``localhost``. This cannot be changed.

You might set this variable in any way you like. On Kubernetes, the easiest way
is likely to be via the Dataverse ``ConfigMap`` (see also :doc:`/day1/config`):

.. code-block:: yaml

  # [...]
  data:
    ENABLE_JMX: "1"

You will need to port-forward this to your host. Example:

.. code-block:: shell

  kubectl port-forward deployment/dataverse 4000 4001 8080

A well known tool for memory, thread and sample analysis is `VisualVM <https://visualvm.github.io/>`_.
After installing and activating the port forwarding, connect VisualVM to
the running JMX service like this:

.. code-block:: shell

  visualvm --openjmx localhost:4000

.. thumbnail:: img/jmx-port.png
  :group: jmx
  :title: Port forwarding with kubectl
  :width: 24%
.. thumbnail:: img/jmx-visualvm-overview.png
  :group: jmx
  :title: VisualVM: overview of connected JVM
  :width: 24%
.. thumbnail:: img/jmx-visualvm-memory.png
  :group: jmx
  :title: VisualVM: memory of connected JVM
  :width: 24%
.. thumbnail:: img/jmx-visualvm-threads.png
  :group: jmx
  :title: VisualVM: threads of connected JVM
  :width: 24%





Debugging with JDWP
^^^^^^^^^^^^^^^^^^^

On startup, when the environment variable ``ENABLE_JDWP=1``, the application
server is configured to listen on port ``${JDWP_PORT}`` defaulting to 9009.

You might set this variables in any way you like. On Kubernetes, the easiest way
is likely to be via the Dataverse ``ConfigMap`` (see also :doc:`/day1/config`):

.. code-block:: yaml

  # [...]
  data:
    ENABLE_JDWP: "1"
    JDWP_PORT: "9009"

You will need to port-forward this to your host. Example:

.. code-block:: shell

  kubectl port-forward deployment/dataverse 9009 8080

Then configure your IDE to connect to the remote debugger. Below is an example
for IntelliJ IDEA:

.. thumbnail:: img/jdwp-idea-port.png
  :group: jdwp
  :title: Port forwarding with kubectl
  :width: 24%
.. thumbnail:: img/jdwp-idea-config.png
  :group: jdwp
  :title: Remote debugger configuration in IntelliJ IDEA
  :width: 24%
.. thumbnail:: img/jdwp-idea-connect.png
  :group: jdwp
  :title: Remote debugger in IntelliJ IDEA connected
  :width: 24%
.. thumbnail:: img/jdwp-idea-breakpoint.png
  :group: jdwp
  :title: Remote debugger at work
  :width: 24%



Hot-Reploy of evolving parts with JRebel
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

On startup, when the environment variable ``ENABLE_JREBEL=1``, the application
server is configured to enable JRebel support on deployment.

You might set this variable in any way you like. On Kubernetes, the easiest way
is likely to be via the Dataverse ``ConfigMap`` (see also :doc:`/day1/config`):

.. code-block:: yaml

  # [...]
  data:
    ENABLE_JREBEL: "1"

Once your application server is up, JRebel communicates with the IDE extensions
via the very same port that you use to access Dataverse in the browser. Please
follow their instructions to configure your IDE plugin.

Below is an example using IntelliJ IDEA and its JRebel Plugin, syncing via
a ``kubectl port-forward`` from localhost into the cluster:

.. thumbnail:: img/jrebel-idea.png
  :title: JRebel in Dataverse Pod enabled in IntelliJ IDEA.

.. danger::

  You will need to raise the RAM limit of the pod when enabling this.
  Dev default 1 GiB RAM is not sufficient, 1.5 GiB (= 750 MiB heap) is bare
  minimum. You might need to add more RAM to your Kubernetes cluster, depending
  on your setup.

.. important::

  Please be aware that you will need a JRebel license to use this timesaving
  feature. Good products have a reasonable price. You have been warned.
  https://www.jrebel.com/products/jrebel

.. seealso::

  In the future, when Dataverse runs on Java JDK 11, one might take a look at
  http://hotswapagent.org. There are only outdated DCEVM patches for JDK 8,
  so this is currently not an alternative.