Celinio A quick way to create an instance on OpenStack is to use Terraform, an open-source Infrastructure-as-Code (IaC) tool developed by HashiCorp. Here is my environment, quickly drawn 😉 : This instance will be provisioned with Linux CirrOS. The Terraform plan that i used : The provider to use to interact with OpenStack is terraform-provider-openstack : … Read more
In the Horizon dashboard, I tried to access the instances section, which is part of the compute service. I got this error : I checked all the running devstack services, they were all running but one : I tried to start this service only but it was not enough. I had to restart all services … Read more
Here are the steps to install OpenStack with DevStack on Ubuntu 20.04.3 LTS. DevStack really simplifies the installation of OpenStack. I followed the steps described here : https://docs.openstack.org/devstack/latest/ 1) First you need to create the user “stack” : sudo useradd -s /bin/bash -d /opt/stack -m stack 2) That user should have no password and have … Read more
Graylog is a platform (free and enterprise) that is useful for log management of aggregated data. It is based on Elasticsearch, MongoDB and Scala. It can display messages and histograms. To send data to a graylog server through an HTTP appender with log4J2, i used the GELF layout with the following configuration : I had … Read more
With the help of Groovy, we can delete a file from a generated project if it meets a condition (for instance if a maven property equals a certain value). Here is the procedure : 1) Create the archetype. To do that, type the following command from the root of a Maven project : mvn archetype:create-from-project … Read more
It is possible to add UML diagrams to the JavaDoc generated during the build phase. The first thing to do is to install Graphviz which is an open source graph visualization software. After installation, add the bin folder (D:\Graphviz\bin for instance) to the PATH environment variable. Then configure the pom.xml : Here i chose to … Read more
Modularity and plug-ability features in Servlet 3.0 specification is also called web fragments. The JSR 315 (Java Servlet 3.0 specification) is already 9 years old. The final release dates back to december 10, 2009. https://jcp.org/en/jsr/detail?id=315 Web fragments are one of the main features of this JSR. A web fragment is an XML file named web-fragment.xml … Read more
So you coded the data layer of your application using JPA (with for instance the Hibernate implementation) and when the application reaches the staging environment, you hear it is too slow ! Too many queries, too long queries, etc. What do you do ? You try to optimize your data layer ! One possible optimization … Read more
Java 8 has an interesting feature that I learnt recently. A variable can become “effectively final”. Very useful. For instance, the following class would not compile in Java 1.7. It would return the following error : “Cannot refer to the non-final local variable myVocabulary defined in an enclosing scope”. It would require to add the … Read more
When checking the issues detected by Sonar, i noticed a few issues related to cyclomatic complexity. The usual message is clear : The Cyclomatic Complexity of this method “checkSomething” is 22 which is greater than 12 authorized. Indeed, the method checkSomething has way too many if conditions : Question : how is the cyclomatic complexity … Read more
If you are behind a corporate proxy, you might end with a connection error while running this command : Here is how to set up Docker so that it works behind a corporate proxy: 1) Edit the Docker VM /var/lib/boot2docker/profile 2) Add these lines at the end of the file : 3) Finally, restart Docker … Read more
Here is a complete and short example of asynchronous development using JMS and a Message-Driven Bean (MDB). First the procedure to configure inside Weblogic Server a JMS server in order to create a queue, then the code for the producer/sender of a message to the queue and then the code for a consumer (MDB). 1) … Read more
By default, Weblogic Server wraps data types such as Struct, Blob, Array, Clob, etc. For instance, oracle.sql.STRUCT becomes weblogic.jdbc.wrapper.Struct_oracle_sql_STRUCT. That can become a problem if for instance you’re expecting a data type : This would raise the following error : To avoid it, one can simply disable that wrapping in the Weblogic administration console : … Read more
I found out that it is important to specify the exact version of Oracle in the persistence.xml file. I am currently using EclipseLink as the persistence framework provider. Oracle hints were introduced to speed up/optimize SQL queries. Starting with Oracle 10, some of them have become almost unecessary because the optimizer was greatly improved. Also, … Read more
I had to find a way to test a method from a stateful session bean (EJB PersonSABean implements PersonSF) defined in a service layer that calls another method from another stateful session bean (EJB HouseSFBean implements HouseSF) defined in a business layer. To call that method from EJB HouseSFBean, the EJB PersonSABean needs to perform a … Read more
It seems to me that the order of execution of the reader, the processor and the writer, inside a step and a chunk, is not always clear in everybody’s mind (included mine when i started with Spring Batch). So I made the following 2 tables that should help – I hope – clarify things. 1) … Read more
I wrote this small class to illustrate the use of the Async and Await keywords which were added in .NET 4.5. It should quickly help anyone curious to understand this easier way to write asynchronous programs in C#. The output below (DOS window) shows clearly the difference between the call of a synchronous method and … Read more
With EclipseLink used as the JPA provider, the following error message “Null primary key encountered in unit of work clone” may appear if the value 0 is used for a field which is a primary key. To resolve it, a few solutions : 1) start your primary key values from 1 instead of 0, which … Read more
Here are the steps to run the super dev mode which is a new feature of GWT 2.5. The versions i used are GWT 2.5.1-rc1 and Chrome 26.0. That version of Chrome requires the latest version of GWT, otherwise it will not work. I tested it with GWT 2.5 previously and I could not see … Read more
Just want to signal something that a lot of Java developers seem not to be aware of : a few of the upcoming features of the JDK 8 have been available in C# for some time now. .NET / C# Java Lambda expressions (closures) .NET 3.5 – C# 3 – 2007 JDK 8 – 2013 … Read more
WebLogic 10.3.5 is JAVA EE 5 certified. However JPA 2 is not part of the JAVA EE 5 (2006) specifications, it is part of the JAVA EE 6 (2009) specifications. So since WebLogic Server implements the Java EE 5 specification, it is not required to support JPA 2. However it is possible to add support … Read more
To print a widget or an entire page with GWT, you can use JSNI and the JavaScript print function. A good practice is to put all the content you want to print inside a DIV tag, for instance : An id is assigned to that DIV tag (line 10) and a button is added to … Read more
Here is my book review of the second edition of the book Programmation GWT 2 (author : Sami Jaber). In French since the book is written in French. Cette deuxième édition fait 21 chapitres (516 pages) alors que la première édition comptait 17 chapitres (461 pages). Soit environ 50 pages supplémentaires. Elle prend en compte … Read more