Monday, February 08, 2016

JHipster Entities, JDL and how to regenerate

I have been playing around with jhipster for 1-2 days now to understand how this could help out on some of our projects. Note that I have been using jhipster on Windows 10 , basically pre-requisites is that you have installed the following :
1. npm
2. Java 8
3. maven 3

We have been using spring-boot for quite some time now on a number of different projects
 and jhipster is an interesting framework to consider on top of spring-boot to quickly setup a project which has :

  1. Security already enabled
  2. Domain layer already configured
  3. Basic AngularJS UI in place for CRUD operations
  4. Metrics information
  5. REST api
  6. Swagger integration
  7. Liquidbase integration
  8. and a host other neat features
Now everything really is based on the entities within your domain model . There are different means of Entity generation :

1. through  command line using : yo jhipster:entity NameofYourEntity 
2. or using jhipster-uml

I prefer the jhipster-uml option as its much faster for you to generate your entities rather than having to go through the command line which is error prone and more time consuming.

Assuming that you have installed jhipster properly the first thing you need to do is to install jhipster-uml using the following command :

npm install -g jhipster-uml

Now for jhipster-uml there are a basically 2 fundamental ways to use it either through:

1. UML editors such as Modelio or UML Designers
2. or using the JHipster Domain Language  (JDL)

In our case we are going to use the  JDL because  its agnostic of any UML tooling , faster and you can provide more options e.g pagination which typically you cannot do with the UML tools as they are not specific to jhipster .

1. So first things first create a directory e.g Parking ( am creating a  sample Parking app )

2. Execute yo jhipster on the directory and follow the standard questions depending on what you want  in terms of project name , packing , caching , websockets etc.., this will roughly take a good 3-5 mins to generate a project depending how fast our internet connection is to download everything , am executing this on a Windows Amazon Ec2 instance and its pretty fast 

3. Now we need to create a .jh file in the root folder which will contain our  Entities , their relationships and the options we want enabled. We will call it parking-uml.jh

4. The file content looks like the following, note that the JDL is pretty straightforward: 

-- parking-uml.jh contents-----------

entity ParkingSpace {
  name String required,
  description String  minlength(5) maxlength(50),
  expiration LocalDate

enum AvailabilityReason {

entity AvailabilitySlot {
  description String  minlength(5) maxlength(50),
  availabilityReason AvailabilityReason required,
  fromDate ZonedDateTime,
  toDate ZonedDateTime

entity BookingSlot {
  description String  minlength(5) maxlength(50),
  fromDate ZonedDateTime,
  toDate ZonedDateTime

relationship OneToMany {
  ParkingSpace{availabilitySlots} to AvailabilitySlot{parkingSpace(name)}

relationship OneToMany {
  ParkingSpace{bookingSlots} to BookingSlot{parkingSpace(name)}

paginate ParkingSpace, AvailabilitySlot, BookingSlot with pagination

service ParkingSpace, AvailabilitySlot, BookingSlot with serviceImpl


The documentation page at jhipster-uml already explains the structure of the JDL so i will not go duplicate information from there in this post , however I will explain some of the stuffs to look out for.

The options paginate and  service need to contain all the entities that share the same pagination option on the same line . For example if you wrote them with same option but on different lines for each entitiy then only the BookingSlot will have pagination within the generated AnjularJS pages , ParkingSpace will have no pagination:

paginate ParkingSpace with pagination
paginate BookingSlot with pagination

However if you have different options per entity then you need to have a line per option eg.

paginate ParkingSpace, AvailabilitySlot with pagination
paginate  BookingSlot with infinite-scroll

Also each time you define a relationship create a specific block for that relationship as shown above.

It took me some amount of time to figure this out as was not explicit within the docs.

Now we are ready to generate the Entities , navigate on command line to the root of the directory and execute :

jhipster-uml parking-uml.jh

This will go about generating a number of classes and AngularJS files .

You will see that there is a .jhipster directory which created in your root directory that contains a number of JSON files representing your entities. Do take the time to open the JSON files to  have a look at the generated data.

Running the application is then pretty straight-forward execute on command line:
mvn spring-boot:run
This will tell maven to launch an instance of the application typically at .

Entities Regeneration

Now the tricky bit is when you need to re-generate your entity classes and I spent hours trying to find the right set of actions so this is what i find works best :

1. update your .jh JDL file in our case its parking-uml.jh with your changes
2. execute a mvn clean this will delete the target directory from all previousy generated classes
3. navigate from within your root directory to src\main\resources\config\liquibase 
4. now edit the master.xml file by removing all the include tags except for  :

<include file="classpath:config/liquibase/changelog/00000000000000_initial_schema.xml" relativeToChangelogFile="false"/>

5. Now go to the changelog sub-directory and delete all xml files except 00000000000000_initial_schema.xml  .

6. We are done with our cleansing , we can regenerate entities using jhipster-uml parking-uml.jh
7. Execute  mvn spring-boot:run to start your app

You should be able to have  now a jhipster app with the updated entities .

Thursday, July 23, 2015

Docker first steps

Currently looking at implementing DevOps based solution at work and whenever you hear DevOps one of the most famous trending buzz work is Docker .

I decided to give it a try on a Windows 7  pc , basically you need to follow the tutorial to install Boot2Docker which will is simple enough in terms of just being an exe that will kick start a stripped down Linux instance on your Windows pc or Mac .

The first thing you need to do is try out this simple command:

docker run hello-world

The picture below explains syntax within the commands:
Now the first issue I got however that no Docker images were being downloaded , i just kept getting i/0 timeout errors . Figureout that something might be blocking the images being downloaded.

A simple googling provided a rapid answer that the problem had to do with Cisco Connect Anywhere , if you have it installed either you need to exit it ( and close from system tray ) or you  can follow the instructions from this stackoverflow query:

Sure enough once Cisco Connect Anywhere was closed i was able to download the image.

Sunday, April 12, 2015

Control GPIO Pins on Raspberry Pi 2 using Webiopi

I recently started working on a robot controlled with my Raspberry Pi , it is at the moment kind of rover which is attached to my Raspberry Pi through a long umbellical cord of wires. There are 2 servos to which my Raspberry Pi sends out data through an L298N H-Bridge which makes the Robot "Rover" wheels  move either backward or forward .

I managed to also write a python code to send signals to the servers which looks a bit like this :

import RPi.GPIO as GPIO
import time



Now that is great but what would have been better would be to access to the GPIO pin remotely via a REST API for example and here is where Webiopi kicks in which basically provides you a WEB and a REST interface to connect to you GPIO pins of your PI :  

As a first setup you need to follow the instructions from the Webiopi install page above .

Note: that current version ,  WebIOPi-0.7.1 ,didn't work straight off with my Raspberry Pi 2 I had to do the following changes to the following c files  once the Webiopi setup was completed:

1.python/native/cpuinfo.c,change "BCM2708" to "BCM2709";
2.python/native/gpio.c, change "#define BCM2708_PERI_BASE 0x20000000" to "#define BCM2708_PERI_BASE 0x3f000000"; again.

The above solution was found from RaspberryPi forums .

Now you should be up and running after having re-run the setup for WebIOPI. You launch the server using command:

sudo /etc/init.d/webiopi start

Then you go to navigate to the following location on your PI :


Note that you can get the IP_ADDRESS_OF_YOUR_PI using ifconfig command .

To quickly test the setup navigate to :

For those pins on which servos are connected change them from IN to OUT  and click on the number corresponding to the pin to execute .


Note that WebIOPI is supported by Weaved which provides you to install a package on your Raspberry PI that allows you to control your RaspberryPi WebIOPI from anywhere as long as  you and your PI are connected to the internet .

What nice is that this is a free service and I justed it works .

Sunday, September 21, 2014

Starting Chromium on the PI in full screen mode

OK this is something fairly easy but do remember that you will do first change your settings on raspi-config to boot on desktop:

1. Step one enter the following command , sudo raspi-config
2. The in the menu select the sub menu to choose where you boot to
3. Select to boot to desktop

Now that has been done you follow the commands to be added as described in the following web page (its all straight forward): 

Then you just reboot using sudo reboot .

Saturday, July 12, 2014

NodeJS / Express and Restful API on the PI

Am now looking at how to provide a restful interface for the PI using NodeJS thankfully there was already a blog entry that explained how to get started with exposing a restful interface ( GET , POST , DELETE) using NodeJS express.

So if you are like me and want to have something clean and easy that gets you up and running check out the following :

All the codes work seamlessly on the Raspberry PI .

I also found a NodeJS plugin which seems very promising to integration with omxplayer at the following link:

I have thus managed to integrate a REST API on the PI that allows me to Post a Request to play a file and it actually calls omxplayer and the video file is played on my HDMI TV.

I will post a sample Express NodeJS file once I have something working well with basic features e.g

1. Controls for pausing , forward etc..
2. Availability to display currently playing file in list
3. Looping
4. Amount of time remaining (no idea if this is achievable)
5. etc..

Saturday, July 05, 2014

No Audio on Raspberry PI

If for some reason you are not getting any audio through omxplayer on your Raspberry Pi , try the following steps:

  1. Execute:  sudo nano /boot/config.txt
  2. Uncomment line:  hdmi_drive=2
  3. Re-start your Raspberry Pi such as it reboots
  4. Connect to your PI again and try to play a file e.g  omxplayer -o hdmi /home/pi/myNAS/myShare/The.Big.Bang.Theory.mp4
The important thing is to use the -o hdmi option.

Mounting a NAS Drive on Raspberry Pi

I got my Pi last year in December and I know i went through the painful task of searching for all the options for configuring my Pi to access a NAS (Network Attached Storage) drive. In my case my Transcend 750GB HD is connected to my Orange Livebox .

Today I decided that I would restart from scratch with my PI installation as OMXPlayer somehow stopped working so am writing this up such as others can quickly setup their NAS drive.

First thing you need to create the following directory on your PI :


this is simple as executing :

  1. mkdir myNAS
  2. then cd myNAS
  3. mkdir myShare
Once you've create the directory you need the following information :

  • Location of your NAS storage device e.g //livebox/myNASLocation
  • Username and password to connect to the NAS device e.g myUsername / myPassword
Then login to your raspberryPi and execute the following command:

  • sudo nano /etc/fstab
You will need to specify the mapping for the NAS within this file simply add a line like the following to the file within the nano editor:
  • //livebox/myNASLocation/  /home/pi/myNAS/myShare cifs username=myUsername,password=myPassword,uid=pi  0 0

Obviously you will need to replace :

  1. //livebox/myNasLocation/  
  2. , myUsername with your actual NAS username
  3. and myPassword  with password for your NAS
-with your own values.

Now do a CONTROL+X  to exit nano , enter Y to save and enter on your Return to exit Nano.

Just to make sure you might want to re-open the file to check whether the settings were correctly saved.

Now that we have added the value , the last thing that to do is to mount the NAS , simply enter the following command :

  • sudo mount /home/pi/myNAS/myShare

Saturday, January 04, 2014

Firing up Raspberry PI omxplayer using Java code

The Pi has an excellent HDMI media player called omxplayer but it fails short in terms of interface to interact with , for starters by default you can interact with it only via command line for example the following command will play an mp4 file:

omxplayer -r -o hdmi myVideoFile.mp4

I have been working on a Spring Boot Restful application to be able to control the OMXPlayer on the Raspberry Pi . For now my Spring Boot application which runs on Raspberry Pi itself only provides a means to play a specified file and to stop the omxplayer .

Now whats interesting is that Spring Boot provides an easy means to quickly put up an executable jar file which can expose Restful endpoints . So next step is how to call the command above from Java on the Pi which is basically a unix system .


Strangely as it sounds it took me a while to figure this out whilst navigating through stackoverflow , well its not that complicated.

All you need is a ProcessBuilder :

ProcessBuilder pb = new ProcessBuilder("bash", "-c", "omxplayer -r -o hdmi myVideoFile.mp4");
Process process = pb.start();

StringBuffer sb = new StringBuffer();

BufferedReader reader = new BufferedReader(new InputStreamReader(

String line = reader.readLine();
while (line != null) {
line = reader.readLine();

The ProcessBuilder will execute a Java process which in turn execute your omxplayer play command on the unix system , the output of this operation is returned back to the sb StringBuffer . 


Currently I couldn't find an elegant way to stop the playback though so what am doing is that am literally killing the process using the kill command e.g :

kill -9 3144

where 3144 is some PID (Process ID) which you need to capture to kill the process (executed through the process builder) , note that each time you fire off the omxplayer it will have a different ID.

Note that I use the following  command to get the PID 

ps -ef |egrep \"/usr/bin/omxplayer.bin

This will give you something as shown in the screenshot below :

Note that in either case you can use the same codes above to execute the :

1. codes that will return you the output from which you can then extract the PID 
2. execute the kill command to stop the process 

So that's as simple as it is for now.