The state of Java [developers] – reflections on Devoxx 2019

I attended Devoxx Belgium – November 2019. The yearly gathering of over 3000 Java developers (numbers provided by Devoxx website). Maybe not all of them Java and perhaps some not even developers. But by and large … Java and software development are the core themes.

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This conference has taken the place of JavaOne as the premier venue for the Java community – to exchange ideas, make announcement, promote open source projects and win the hearts (more...)

Node JS application running on GraalVM – interoperating with Java, Python, R and more

When you install GraalVM, one of the things you get is a Node runtime environment (GraalVM 19.2.1 is based on Node 10.16.3 – with support for the core Node libraries and un understanding of NPM modules – and has a JavaScript engine that is ECAMScript 2019 compliant). Instead of V8, the usual JavaScript execution engine, this GraalVM environment leverages GraalJS and the JVM as execution platform. GraalJS runs Java Byte code (more...)

DBeaver for PostgreSQL

I’m migrating my database classes from the Oracle database to the PostgreSQL database. Using the Oracle Express Edition has always required a virtualized image because students use Windows and Mac OS. Also, the university doesn’t like my use of a virtualized image. Virtualization imposes incremental cost on students to have high end laptops.

The available Docker images don’t typically support the Oracle Express Edition. That means there are licensing implications tied to Oracle.

As a (more...)

Java and Postgres

I wanted to get Java working with PostgreSQL to test some GUI interfaces on Linux. Figuring out the necessary JAR file for the JDBC was my first hurdle. I found it was postgreSQL-42-2.5.jar file.

You can download it with the following command line:

wget https://jdbc.postgresql.org/download/postgresql-42.2.5.jar

I downloaded it to a Java directory off the home/student directory. Then, I added the following CLASSPATH to local java.env environment file.

 (more...)

Python application running on GraalVM and Polyglotting with JavaScript, R, Ruby and Java

GraalVM is among other things a polyglot language runtime. It can run applications written in many languages – JVM languages like Java, Scala, Groovy and Kotlin as well as non-JVM language such as Python, R, Ruby, JavaScript and LLVM. GraalVM also allows applications in any of these languages to execute code snippets written in any of the other languages it supports. It is like the cab driver that can speak many languages and also is (more...)

Lambda Function to Resize EBS Volumes of EMR Nodes

I have to start by saying that you should not use EMR as a persistent Hadoop cluster. The power of EMR lies in its elasticity. You should launch an EMR cluster, process the data, write the data to S3 buckets, and terminate the cluster. However, we see lot of AWS customers use the EMR as a persistent cluster. So I was not surprised when a customer told that they need to resize EBS volume automatically (more...)

Create a Native Image Binary Executable for a Polyglot Java Application using GraalVM

imageGraalVM provides a runtime component that enhances the JVM in several ways. It makes the JIT compilation better. It also allows the JVM to run non-JVM languages such as JavaScript, R, Python, Ruby and LLVM. And it makes it possible for languages running on the JVM to interact – through the polyglot interoperability. Another valuable capability of GraalVM is called native image generation. This feature allows us to use Ahead of Time Compilation of a (more...)

Oracle Database: Write arbitrary log messages to the syslog from PL/SQL

Syslog is a standard for message logging, often employed in *NIX environments. It allows separation of the software that generates messages, the system that stores them, and the software that reports and analyzes them. Each message is labeled with a facility code, indicating the software type generating the message, and assigned a severity level.

In *NIX systems syslog messages often end up in /var/log/messages. You can configure these messages to be forwarded to remote syslog (more...)

Leverage NPM JavaScript Module from Java application using GraalVM

imageInteroperability from Java to JavaScript has been an objective for the Java community for quite a while. With GraalVM, there is great way to run JavaScript code from within Java applications. The interaction itself is faster, more robust and more ‘native’ (rather than bolt-on) than earlier mechanisms. For developers, the interaction is easy to implement. And this opens up great opportunities for leveraging from Java many of the great community resources in the JavaScript community (more...)

Calling out from Java to JavaScript (with call back) – leveraging interoperability support of GraalVM

imageInteroperability from Java to JavaScript has been an objective for the Java community for quite a while. With Rhino and later Nashorn, two valiant attempts were made to add scripting interaction to the JDK and JVM. Now, with GraalVM, there is a better alternative for running JavaScript code from within Java applications. The interaction itself is faster, more robust and more ‘native’ (rather than bolt-on). For developers, the interaction is easier to implement. And as (more...)

Postgres Print Debug Notes

A student asked how you print output from PL/pgSQL blocks. The student wanted to know if there was something like the following in Oracle’s PL/SQL programming language:

dbms_output.put_line('some string');

or, in Java programming the:

System.out.println("some string");

The RAISE NOTICE is the equivalent to these in Postgres PL/pgSQL, as shown in the following anonymous block:

do $$
begin
  raise notice 'Hello World!';
end;
$$;

It prints:

NOTICE:  Hello World!

I hope (more...)

Amazon QLDB and the Missing Command Line Client

Amazon Quantum Ledger Database is is a fully managed ledger database which tracks all changes of user data and maintains a verifiable history of changes over time. It was announced at AWS re:Invent 2018 and now available in five AWS regions: US East (N. Virginia), US East (Ohio), US West (Oregon), Europe (Ireland), and Asia Pacific (Tokyo).

You may ask why you would like to use QLDB (a ledger database) instead of using your traditional (more...)

Sample AWS Lambda Function to Monitor Oracle Database

I wrote a very simple AWS Lambda function to demonstrate how to connect an Oracle database, gather the tablespace usage information, and send these metrics to CloudWatch. First, I wrote this lambda function in Python and then I had to re-write it in Java. As you may know, you need to use cx_oracle module to connect Oracle Databases with Python. This extension module requires some libraries which are shipped by Oracle Database Client (oh God! (more...)

Getting Started With Redis Streams & Java

Read this article on my new blog As you may have seen, I have joined Redis Labs a month ago; one of the first task as a new hire is to learn more about Redis. So I learned, and I am still learning. This is when I discovered Redis Streams. I am a big fan of streaming-based applications so it is natural that I start with a small blog post explaining how to use Redis Streams and Java. (more...)

First episode of the bol.com TechLab podcast

First episode of the bol.com TechLab podcast

Today we released the first episode of the bol.com TechLab podcast. The subject of this first episode is our Kotlin adoption journey.

In this podcast, we share our experience with you to learn and entertain. Peeking behind the screens of IT and Tech in general at bol.com. Showing you our approach to IT, e-commerce and retail platforms. We have a lot of fun creating the (more...)

Lies, darn lies and sampling bias

Sampling profiling is very powerful technique widely used across various platforms for identifying hot code (execution bottlenecks).

In Java world sampling profiling (thread stack sampling to be precise) is supported by every serious profiler.

While being powerful and very handy in practice, sampling has well known weakness – sampling bias. It is real and well-known problem, though its practical impact is often being over exaggerated.

A picture is worth a thousand of words, so let (more...)

Intercepting ADF Table Column Show/Hide Event with Custom Change Manager Class

Ever wondered how to intercept ADF table column show/hide event from ADF Panel Collection component? Yes, you could use ADF MDS functionality to store user preference for table visible columns. But what if you would want to implement it yourself without using MDS? Actually, this is possible through custom persistence manager class. I will show you how.

If you don't know what I'm talking about. Check below screenshot, this popup comes out of the box (more...)

Java 11: JEP 333 ZGC A Scalable Low-Latency Garbage Collector

After i found this strange "No-Op Garbage Collector", i was keen, if there are some other new GC features with Java 11.


There is another JEP with the number 333:
 If you look here, the goals are:

  • GC pause times should not exceed 10ms
  • Handle heaps ranging from relatively small (a few hundreds of megabytes) to very large (many terabytes) in size
  • No more than 15% application throughput reduction compared to using G1
  • (more...)

Java 11: JEP 318 Eplison / A No-Op Garbage Collector

This week i read about the new JDK Enhancement Proposal (JEP) of Java 11.
One of my favourites is JEP 318:

The summary of this JEP says:
Develop a GC that handles memory allocation but does not implement any actual memory reclamation mechanism. Once the available Java heap is exhausted, the JVM will shut down.
For which scenario could this garbage collector be useful?

If you skip to the "motivations" at the JEP, i (more...)

Oracle ADF BC Reusing SQL from Statement Cache

Oracle ADF BC by default is trying to reuse prepared SQL query from statement cache. It works this way when ADF BC runs with DB pooling off (jbo.doconnectionpooling=false). Normally we tune ADF application to run with DB pooling on (jbo.doconnectionpooling=true), this allows to release unused DB connection back to the pool when a request is completed (and in this case, statement cache will not be used anyway). If View Object is re-executed multiple (more...)