Showing posts with label docker. Show all posts

Thursday, 8 May 2025

Releasing unused but committed Heap memory

As mentioned in the references below, with some commandline arguments to the JVM, you can force periodic Garbage Collection cycles when on low load to reclaim memory that isn't used (because it's not doing anything).

This comes in handy when using containers, where committed unused memory in the node just costs money.

The application is considered inactive, and G1 triggers a periodic garbage collection if the following conditions hold:

G1PeriodicGCInterval: number of milliseconds have passed since any previous garbage collection pause and there is no concurrent cycle in progress at this point. A value of zero indicates that periodic garbage collections to promptly reclaim memory are disabled.
G1PeriodicGCSystemLoadThreshold: The average one-minute system load value as returned by the getloadavg() call on the JVM host system (e.g. container) is below this value. A value of zero means this is ignored.

As an example:

java -server -XX:+UnlockExperimentalVMOptions -XX:+UseStringDeduplication -XX:+UseG1GC \
-XX:G1PeriodicGCInterval=30000 -XX:G1PeriodicGCSystemLoadThreshold=0.5 \
-Xmaxf0.3 -Xminf0.1 -Xmx2048M -Xms32M \
-jar ../releases/mrbear.war

This example would indicate that every 30 seconds, if the average system load is below 0.5, a Garbage Collection cycle may be initiated to reclaim memory.

Java Agent

In the past Virtuozzo, which I used, had to put in a java-agent in the command line to have the same functionality. So this is no longer necessary.

Progress!

References

Virtuozzo - Elastic JVM with Automatic Vertical Memory Scaling: https://www.virtuozzo.com/company/blog/elastic-jvm-vertical-scaling/
JEP 346: Promptly Return Unused Committed Memory from G1: https://openjdk.org/jeps/346

Friday, 9 June 2023

Podman

Podman is a drop-in replacement for Docker, at least that's what I hear.

From the little experience I currently have, the commands on the command line seem to be almost equivalent if not in syntax at least in intention to Docker.

Installing Podman

mrbear % brew install podman

Running Podman

podman machine init
Downloading VM image: fedora-coreos-38.20230514.2.0-qemu.aarch64.qcow2.xz: done
Extracting compressed file
Image resized.
Machine init complete
To start your machine run:

podman machine start

podman machine start
Starting machine "podman-machine-default"
Waiting for VM ...
Mounting volume... /Users:/Users
Mounting volume... /private:/private
Mounting volume... /var/folders:/var/folders

This machine is currently configured in rootless mode. If your containers
require root permissions (e.g. ports < 1024), or if you run into compatibility
issues with non-podman clients, you can switch using the following command:

podman machine set --rootful

API forwarding listening on: /Users/mrbear/.local/share/containers/podman/machine/qemu/podman.sock

The system helper service is not installed; the default Docker API socket
address can't be used by podman. If you would like to install it run the
following commands:

sudo /opt/homebrew/Cellar/podman/4.5.0/bin/podman-mac-helper install
podman machine stop; podman machine start

You can still connect Docker API clients by setting DOCKER_HOST using the
following command in your terminal session:

export DOCKER_HOST='unix:///Users/mrbear/.local/share/containers/podman/machine/qemu/podman.sock'

Machine "podman-machine-default" started successfully

Verify Podman

podman info

A GUI

I will be trying out Podman Desktop. Under Docker I was very used to Portainer.

Networking

Non-root containers use slirp4netns and have no routable IP address. Root containers use netavark.

Glossary of commands

podman machine init

initializes the machine

podman machine start

starts the machine

podman info

verify installation

podman ps [-a]

list creating and running containers

podman pull <container url>

pull an image, for example "podman pull docker.io/library/postgres:14" or simply "podman pull mariadb"

podman images

show all images

podman rmi <image>

remove an image, for example "podman rmi 0c1418f4071b", where the id can be ascertained using "podman images"

podman run ...

run a container, for example:

podman run --detach --tty --name webserver --publish 8080:80 quay.io/libpod/banner
podman run --name postgres --detach --publish 5432:5432 --env POSTGRES_USER=admin --env POSTGRES_PASSWORD=Passw0rd postgis/postgis
podman run --name postgres --detach --publish 5432:5432 --env POSTGRES_USER=admin --env POSTGRES_PASSWORD=Passw0rd docker.io/library/postgres:latest
podman run --detach --name mariadb --publish 3306:3306 --env MARIADB_USER=root --env MARIADB_PASSWORD=Passw0rd --env MARIADB_ROOT_PASSWORD=Passw0rd docker.io/library/mariadb

--detach/-d: run the container in the background and print the new container ID. The default is false.
--tty/-t: Allocate a pseudo-TTY. The default is false.
--publish/-p [[ip:][hostPort]:]containerPort[/protocol]¶: Publish a container’s port, or range of ports, to the host.
--env/-e: Set environment variables.
--name: Assign a name to the container.

podman ps

lists the running containers on the system. Use the --all flag to view all the containers information.

podman attach <container_id>

sttached tty to a running container

podman inspect -l

metadata and details about the running containers

podman logs <container_id>

log container logs

podman top <container_id>

show processes running in the container

podman start <container_id>

start a container

podman stop <container_id>

stop a container

podman rm <container_id>

remove a container

I'll add to this as I get more information.

References

Podman: https://podman.io/
Podman - Installation: https://podman.io/docs/installation
TechViewLeo - How To Run PostgreSQL 14|13 in Podman Container: https://techviewleo.com/how-to-run-postgresql-in-podman-container/?utm_content=cmp-true
podman desktop: https://podman-desktop.io/
ImaginaryCloud - Podman vs Docker: What are the differences?: https://www.imaginarycloud.com/blog/podman-vs-docker/
Portainer: https://www.portainer.io/

Thursday, 7 October 2021

Running Payara Micro on Java 11 via GraalVM on Docker on Jelastic

Boy, that title was a mouth full.

Now if you want more information on Docker, you can check out reference [3]. Or if you're looking for Java 11 GraalVM Dockerimages suitable for Jelastic, you can check out [1] and [2].

This blog is more about the contents of the Dockerimage than Docker itself.

GraalVM

Well, I've been using Jelastic for a while now, and it suited my needs, until it didn't.

They provide GraalVM out of the box, but not the Java 11 version yet.

I was using a Payara Server image for Jelastic, and I had good results just installing GraalVM on the Image afterwards and run Payara using that, but I was looking for something a little more lean.

Sooo, in short, I used the GraalVM image used by Jelastic as a baseline in my Docker image (jelastic/javaengine:graalvm-21.0.0.2).

Then it was just install the JDK11 version of GraalVM and create my Image.

Less troublesome than I thought it would be.

Payara Micro

So Payara Micro is awesome. The way this differs from Microprofile, is that Microprofile contains only Microprofile and the Payara Micro basically seems to be a small Payara server run from the command line. It is based off the Payara Embedded Web release. See [4].

So there's basically two things:

you run it from the command line using java and the payara-micro-5.2020.7.jar
you provide a postboot file containing the settings

Example

Let's try an example.

The example basically runs a Payara Micro instance, with some wars deployed and a JDBC library for connecting to a database.

All configuration of the database connection is done using the afore mentioned postboot file.

Some notes on the postboot file.

I am not interested in Hazelcast, so I turned this off. The main result should be faster startup.
I added eclipselink.target-database to the jdbc string, otherwise the JDBC driver will identify itself as MariaDB driver, and it is unknown. You can immediately tell by the following error message in the log:
Not able to detect platform for vendor name [MariaDB[10.4.20-MariaDB, 10]]. Defaulting to [org.eclipse.persistence.platform.database.DatabasePlatform]. The database dialect used may not match with the database you are using. Please explicitly provide a platform using property "eclipselink.target-database".
I also added a config property to it. Microprofile (which is included) has support for Configuration. And it's great!

Secure Socket Layer

There's a simple self signed SSL Certificate included in the Payara Micro, which works fine, unless, like me, you wish to use a genuine SSL Certificate.

The idea here is to expand on the command line (see above in run.sh) with SSL options, for example as follows:

-Djavax.net.ssl.trustStore="/home/jelastic/cacerts.jks"
-Djavax.net.ssl.keyStore="/home/jelastic/keystore.jks"
-Djavax.net.ssl.trustStorePassword="changeit"
-Djavax.net.ssl.keyStorePassword="changeit"

References

[1] Dockerhub - my jelastic graal with jdk 11 docker image: https://hub.docker.com/r/maartenl22/jelasticgraaljdk11
[2] Github - Docker file: https://github.com/maartenl/jelasticgraaljdk11
[3] MyBlog - Docker: https://randomthoughtsonjavaprogramming.blogspot.com/2021/06/docker.html
[4] Payara Micro Documentation: https://docs.payara.fish/community/docs/documentation/payara-micro/payara-micro.html
Releases - graalvm/graalvm-ce-builds: https://github.com/graalvm/graalvm-ce-builds/releases
How to install GraalVM on Linux with alternatives: https://gist.github.com/ricardozanini/fa65e485251913e1467837b1c5a8ed28
GraalVM - GraalVM Community Images: https://www.graalvm.org/docs/getting-started/container-images/
Github - graalvm-ce: https://github.com/orgs/graalvm/packages/container/package/graalvm-ce

Wednesday, 16 June 2021

Docker

$ sudo systemctl start docker

Configuration

I am on a low bandwith thing, so needed to add max-concurrent-uploads to the /etc/docket/daemon.json, otherwise I got connection timeouts. (default is 5)

{
  "experimental": false,
  "max-concurrent-uploads": 1,
  "data-root": "/mnt/docker" }

I've since moved the docker data directory ("data-root") to a separate mount ("/mnt/docker"), as it takes up a deal of space.

See reference 1.

Basics

docker pull dockerimageurl: downloads a particular image, probably from Docker Hub
docker images: can show you all the images the docker has at its disposal
docker container create: creates a new container based on an image
docker run --rm -i -t -p portext:portint dockerimageurl: start running a new container (-d is detached, -p is portmap, -i keep STDIN open even if not attached , -t allocates a pseudo-TTY, --rm removes container on exit ), basically does all of the previous steps if necessary

Administration

docker inspect dockerimageurl: shows low level information on the running container
docker exec <container-id> cat /data.txt: run a single command on the container, can be run as long as the master process (pid 1) is running
docker ls [-a]: seems to be exactly the same as ps
docker ps [-a]: list docker containers (-a for aboth started and stopped)
docker attach <the-container-id>: stttach to a running docker container with the ID from docker ps. Convenient if you've run it "detatched".
docker stop <the-container-id>: stop docker container with the ID from docker ps
docker rm <the-container-id>: remove docker container
docker rmi <the-image-id>: removes an image

Examples

Simply running an image can be done with:

docker run --rm -i -t -p 80:8080 -p 443:8181 --name jelasticgraaljdk17 jelastic/javaengine:graalvm-21.0.0.2

"--name" is a nice option to prevent docker from assigning meaningless auto-generated names to your containers.

It will help tremendously if we could look at how an original image was made. This is possible with the history command.

docker history jelastic/javaengine:graalvm-21.0.0.2

Add --no-trunc to show entire command lines.

For example in the example, it will show the following:

IMAGE	CREATED	CREATED BY	SIZE
72627645230f	12 days ago		24.4MB
<missing>	12 days ago	/bin/sh -c #(nop) WORKDIR /etc/init.d	0B
<missing>	12 days ago	/bin/sh -c #(nop) LABEL actions=webAccess a…	0B
<missing>	12 days ago	/bin/sh -c #(nop) EXPOSE 21 22 25 80 8080	0B

Added 443 8743 to the exposed ports in my new image.

Creating your own image

docker build: build a new container image based on a Dockerfile. (-t is tag)
docker commit c16378f943fe rhel-httpd:latest
docker login -u YOUR-USER-NAME: logging into the Docker hub
docker tag c16378f943fe YOUR-USER-NAME/name: tag your image appropriately before pushing it to the repo
docker push imagename:tag: pushes an image to a remote Docker repository. If you do not provide a tag, it will automatically become "latest".

Examples

cd ../graalvm
docker build -t maartenl22/jelasticgraaljdk11:latest -t maartenl22/jelasticgraaljdk11:v0.1 .
cd ../karchan
docker build -t maartenl22/karchan:latest -t maartenl22/karchan:v2.0.8 .

Check that this worked by running:

docker run --name graalvm --rm -i -t -p 8080:8080 -p 8743:8743 maartenl22/jelasticgraaljdk11:latest
docker run --name karchan --rm -i -t -p 8080:8080 -p 8743:8743 maartenl22/karchan:latest

Pushing your image to Docker Hub

Examples

docker build -t maartenl22/jelasticgraaljdk11 .

docker build -t maartenl22/karchan .

docker image ls

First do this, just to make sure:

docker logout

docker login

docker push maartenl22/jelasticgraaljdk11

docker push maartenl22/karchan

You should see both jelasticgraaljdk11 and registry-host:5000/maartenl22/jelasticgraaljdk11 listed.

You should see both karchan and registry-host:5000/maartenl22/karchan listed.

docker run --name karchan -cap-add=NET_ADMIN --rm -i -t -p 8080:8080 -p 8743:8743 jelasticgraaljdk11:latest

The -cap-add=NET_ADMIN is necessary to see the iptables configuration.

cd /home/jelastic
java -jar payara-micro-5.2021.1.jar --port 80 --sslport 443 jakartaee-8-project.war

Portainer

Portainer is a docker image containing a simple server that interfaces with the Docker deamon. With it you can get a good view of what Docker is running and what containers and images are available and all that.

Also attaching a terminal via de website is possible. Very nice.

docker volume create portainer_dataa
docker run -d -p 8000:8000 -p 9000:9000 --name=portainer --restart=always -v /var/run/docker.sock:/var/run/docker.sock -v portainer_dataa:/data portainer/portainer-ce

When starting it for the first time, and surfing to localhost:9000, you can add an administrator user.

It works great to get a good overview about what's going on.

Hello, world.

References

[1] GuguWeb - HOW TO MOVE DOCKER DATA DIRECTORY TO ANOTHER LOCATION ON UBUNTU: https://www.guguweb.com/2019/02/07/how-to-move-docker-data-directory-to-another-location-on-ubuntu/
Jelastic - Build software stack container image for private PaaS: https://jelastic.com/blog/build-software-stack-container-image-private-paas/
Jelastic - Building custom containers: https://docs.jelastic.com/building-custom-container/
Docker - Custom container deployment: https://docs.jelastic.com/custom-containers-deployment/
Docker - Installing fedora: https://docs.docker.com/engine/install/fedora/
Docker - Reference manuals: https://docs.docker.com/reference/
Portainer: https://www.portainer.io/
Youtube - Intro to Docker [with Java Examples]: https://youtu.be/FzwIs2jMESM
Dockerhub - my jelastic graal with jdk 11 docker image: https://hub.docker.com/r/maartenl22/jelasticgraaljdk11
Github - Docker file: https://github.com/maartenl/jelasticgraaljdk11

Thursday, 17 November 2016

Workshop Continuous Delivery with Docker

Last Monday, on the 14th of November, I got a chance to attend a little workshop on Docker organised by OV Software. It was at the NH Hotel near the facilities of OV Software in The Hague. It is a little far from my place of residence, but I could tag along with a colleague of mine, which helped.

They did a great job of preparing the workshop properly. A VirtualBox image was provided (https://goo.gl/XUM898). The downloaded file can be "imported" (File -> Import Appliance) into the VirtualBox platform (version minimum is 5.0).

Unfortunately, my labtop is not one of the greatest, and the amount of memory required is too much for it. I had to borrow a labtop from work. If this keeps up, I'll have to buy something better for myself one of these days.

Also, unfortunately, I was unable to attend a previous workshop of which this workshop is a followup, so I did miss some background on Docker, and this was my first foray into this new area. Thankfully, a lot can be found on the internet^{1 2}, and I already had plenty of experience with Linux, Java, Maven, and just software development in general.

I had small problems getting it to run, for example:

I had Vx extentions turned off in the BIOS of my labtop. I needed to turn them on.
PAE - Physical Address Extentions was turned off. It should be on.
Somehow, when importing the image, I had turned the machine to 32bits. It's a Linux 64bits image.
It seems it sometimes helps to turn off your USB in the Virtual Machine settings.

The workshop was provided by an employee of OV Software, Jeroen Peeters, who is an excellent and calm speaker.

One of the first things where I went wrong is thinking that Docker is a kind of Virtualisation. It is not. Docker runs within the same Operating System and the containers also all run in the same Operating System. The images, however, can contain everything the container needs to properly run the image. So, they are simply processes running under the same kernel with the same kernel libraries at their disposal, but it is true that these processes are a little better isolated from the rest of the system.

There are plenty of alternatives to Docker, but Docker seems to be the main menu these days:

LXC
Rocket, tooling for developers and systemmanagement
Lmctfy
OpenVZ
Canonical LXD, a Ubuntu thing but more isoltation, so more Virtualisation as it also runs system images

To be more specific, the workshop was regarding Continuous Delivery^{3 4} with Docker.

During the workshop we set up the following Docker containers inside Docker running on Linux Lite 3.0 LTS (Ubuntu based):

a container of GitLab that held a git repository of a Java Program
a container of Jenkins
a maven container (for inside Jenkins)
a tomcat container
a load balancer container (Haproxy)
a testx container⁶

So a webhook in the GitLab repo made sure that jenkins was notified if the source code had changed. Jenkins would therefore start a build pipeline, that would build the application and deploy it on Tomcat and would start testing it using TestX⁵ (a frontend tester tool sauce over protractor and Selenium).

The github repository containing the Java application can be found at https://github.com/jeroenpeeters/docker-workshop-java-todolist/. It is a simple TODO list registration tool.

All this is running in one virtual server. For clustering and the like, you could have a look at Kubernetes, the google solution for running Docker on several machines. Complexity is quite high. But there are also other solutions.

It looks very interesting if you are interested in using Continuous Delivery. I do know that System Management (where I work) is very apprehensive about it. I think they fear to lose control on what Developers can do. We are already working with it in some fashion, but it needs to be improved.

References

[1] Docker: https://www.docker.com/
[2] Docker - Installation on Fedora: https://docs.docker.com/engine/installation/linux/fedora/
[3] Continuous Delivery: Reliable Software Releases through Build, Test, and Deployment Automation: https://www.amazon.com/dp/0321601912?tag=contindelive-20
[4] MartinFowler.com - ContinuousDelivery: http://martinfowler.com/bliki/ContinuousDelivery.html
[5] TestX: https://github.com/testxio/testx
[6] TestX Docker Image: https://hub.docker.com/r/testx/protractor/
Nginx - Docker for Java Developers: https://www.nginx.com/resources/library/docker-for-java-developers/
The Docker Book - Containerization is the new virtualization: https://www.dockerbook.com/
Jenkins: http://www.jenkins.io

Thursday, 5 November 2015

J-Fall 2015

“Once you stop learning, you start dying.”

- Albert Einstein

I just got back from J-Fall 2015¹.

Seeing as the location had been changed from Nijkerk to Ede, I was unable to attend the Early Bird sessions, much to my dismay. I did manage to hitch a ride with a colleague of mine, but in the future, I will try and get a train. The connection seems to be quite good and once more there is a shuttle bus riding between the location (Cinemec) and the trainstation.

What with traffic (congestion) and my colleague sleeping late, I did miss the first keynote (The Experimental Enterprise - Keynote ING), only arriving at the destination at around 09:45.

The list of sessions I witnessed:

Pushing the limits of Continuous Delivery - Keynote Quintor

Provided by Rene Boere and Pascal Snippen

A fascinating view on what Quintor uses to provide Continuous Delivery (CD) using Docker, Apache Mesos, Marathon and Consul combined with HAProxy. The use of container ships to emphasise Docker was inspired and probably is starting to be overused by now. The microservices landscape is large and you can no longer see the forest for the trees, test environments are hard to set up, deployments are complex and timeconsuming.

Automation of Continuous Delivery is the answer.

Microservices for Mortals

Provided by Bert Ertman

This lecture could be construed as a big, huge, warning if you wish to use Microservices. It had a metaphore comparing coding practices with Italian food. The old way of coding compares to Spaghetti. Then SOA (Service Oriented Architecture) was introduced and those layered coding practices compare to Lasagna. Now the new Microservices compare more to Ravioli (tight independent containers of code bundled together) with sauce. The main idea behind microservices seems to be the ability to easy adapt to change. There is no hard definition on what microservices are. Apparently, microservices are small enough to just replace them with a completely new implementation, or just run 10 instances of one easily. They do away with a lot of items we are software developers have gotten used to:

synchronous programming models
ACID
code reuse
using abstractions

Instead, because of the characteristics of Microservices, you get:

asynchronous programming models
any constraints need to be taken care of at the application level
code duplication, each micro service is independent of the others, so code reuse between microservices doesn't make sense
separate data storages (one data storage per microservice)
passing data using websockets or binary protocols or messaging (REST is too much overhead, I don't want to even mention XML. It's all fine for a public API though.)
prefer conventions over abstractions (see code reuse)

If you have not been doing Devops, you cannot get started using Microservices without getting into a world of hurt.

Code for failure. Microservices are brittle, the distributed asynchronous models make them so. Design for this! Use fail early, use resilience patterns, use redundancy, etc.

10 Awesome Tips for Enterprise Javascript - Oracle

Provided by Geertjan Wielenga

This lecture provided an excellent overview of the current JavaScript landscape. I especially liked the fact that he mentioned that at the end of the lecture the landscape will probably already have changed. The JavaScript ecosystem is in that much flux.

Nowadays we have multiple devices, all with different screensizes requiring responsive design. One common factor in all these devices, is that all of them possess a browser. And the Single Page Application (SPA) is becoming the internet-enabled "application" of choice. Page navigation is irrelevant when it comes to Single Page Applications, yet for most Java-based Web Frameworks, page navigation is still an important part of their programming model.

Also, resist the hype. Apparently most managers make bad architecture decision based on hype. And you, as a developer, shouldn't want that.

For some applications, Javascript actually doesn't make any sense. The example provided was air traffic controllers. But different architectures can play different roles, even in those applications where Javascript doesn't make any sense. for example:

mobile apps: notifications
web apps: reporting to (upper) management
application itself: what users actually need and use in day-to-day work

NetBeans provided really nice point-and-click programming of the new HTML 5 components. The new HTML 5 components look very snazzy. Apparently, every new HTML 5 component is itself composed of sub-html-components, called the Shadow DOM and can therefore be styled appropriately. CSS has been split up into approximately 50 CSS modules. JavaScript can be used to avoid having to hide HTML using CSS, because hiding certain HTML components still makes the browser get the linked resources contained in those HTML components. Especially on mobiles this can make a huge difference.

In the Java world, the acronym WORA (Write Once Run Anywhere) is very well known. In the JavaScript world its WONTA (Write Once, Never Touch Again). The projects are so small, and the evolution of the Javascript ecosystem is so quick, it makes more sense to re-design and re-write everything from scratch when required.

Oracle has defined a Javascript framework, which is basically a bundling of common javascript libraries, into what is called the "Oracle Javascript Extention Toolkit"².

“Javascript is the assembly language of the web.”

Then there's, if you really do not want to touch JavaScript with a ten-foot pole, the transpilers:

Dukescript: write Java, but also HTML and CSS. Combine those.
GWT/Vaadin: provides a Java backend similar to the Swing toolkit, and translates your code into HTML,CSS and JavaScript for the frontend.
Dart: separate programming language for the web/mobile/desktop.
Typescript: provides static typing to javascript, a sort of superset of JavaScript following ECMA recommendations that is transpiled to JavaScript
Coffeescript: programming language that translates to javascript

The Java renaissance continues - Keynote Oracle

Provided by Sharat Chander

A motivating speech on the fact that Java is still a success primarily because of the community. And a personal appeal to every person there to connect to at least two in the audience during the conference.

Devops - Are you walking or still talking? - Keynote Capgemini

Provided by Remko Reinders

A lecture on Devops, more importantly, what it takes for an organisation to become a success at Devops and what you can do to help your organisation and yourself to become a success as well.

“Most people will talk the talk. Few will walk the walk. Be amongst those few.”

- Steve Maraboli

“Software is eating up the world.”

- Marc Andreessen, Wall Street Journal

Building Asynchronous and Non-Blocking HTTP Applications with Ratpack

Provided by Hubert Klein Ikkink

My first introduction to Ratpack³, which I had never heard of before. It is a small webserver, that can be programmed using Java 8 and Groovy. It uses Netty for the HTTP IO, has a very small footprint, is very fast and is asynchronous. Does not provide JEE, does not follow the Servlet API and can be started by running a Jar file. Spock is used for testing.

If you want a quick webserver to dish out some REST stuff in a distributed environment, this is it. Check his webblog⁴ for more information.

Java modularity, life after Java 9 - Luminis

Provided by Sander Mak & Paul Bakker

“Good fences make good neighbours.”

- Proverb

An excellent talk about the upcoming Jigsaw in Java 9. It provides a faster startup and a smaller footprint, essential for small devices. It compared what little information there is about Jigsaw to the existing implementation of OSGI. Modules are allowed to talk to other modules only by the service contract each module provides. Modules are defined in a module-info.java file. The segregation is looked after by the VM itself and cannot be circumvented. Layers are used to prevent different versions of the same module interfering with each other. Versioning isn't really built into the new system. There is a linking tool called jlink and module maker tool called jmod. Jdebs can provide your program with which modules it needs. Identification of a module is done using a newly defined namespace specific for modules.

Classpath scanning for annotations is going to be a problem. It is going to have to be service-oriented in the future.

Especially application servers are going to need a major overhaul, as well as several annotation-crosscutting concerns frameworks as REST and JPA implementations.

See http://bit.ly/java9demo for more information.

References

[1] NLJUG - J-Fall 2015: http://www.nljug.org/jfall/2015/
[2] Oracle JavaScript Extention Toolkit: http://oraclejet.org
[3] Ratpack: https://ratpack.io/
[4] Mr Haki's Webblog: http://mrhaki.blogspot.nl/