Jul 27, 2021

Configuring and Using GitHub Readme Instant Preview

GitHub will render project README and other markdown files to HTML when displaying projects on its website. Those files must be commited and pushed before the developer can see the results which can result in extraneous and unwanted commits. This post discusses installing and using the GitHub Readme Instant Preview (GRIP) tool for previewing GitHub-flavored Markdown locally.

Jun 14, 2021

Ganymede Kernel Released

Ganymede Kernel is released.

The Ganymede Kernel is a Jupyter Notebook Java kernel based on JShell combined with an integrated Apache Maven-like POM, support for JVM languages such as Groovy, Javascript, and Kotlin, and support for Apache Spark and Scala binary distributions.

Oct 31, 2020

Spring Boot Part 7: Spring Security, Basic Authentication and Form Login, and Oauth2

This article explores integrating Spring Security into a Spring Boot application. Specifically, it will examine:

  1. Managing users’ credentials (IDs and passwords) and granted authorities

  2. Creating a Spring MVC Controller with Spring Method Security and Thymeleaf (to provide features such as customized menus corresponding to a user’s grants)

  3. Creating a REST controller with Basic Authentication and Spring Method Security

Aug 11, 2020

java.util.concurrent.ForkJoinPool Example

The combination of RecursiveTask implementations running in a ForkJoinPool allows tasks to be defined that may spawn subtasks that in turn may run asynchronously. The ForkJoinPool manages efficient processing of those tasks.

This article presents a simple calculator application to evaluate a formula defined as a List presents a single-threaded recursive solution, and then converts that solution to use RecursiveTasks executed in a ForkJoinPool.

Jul 19, 2020

Spring Boot Part 6: Auto Configuration and Starters

Spring Boot allows for the creation of “starters:” Convenient dependency descriptors that often provide some specific but complex functionality. Examples from Spring Boot discussed in this series of articles include spring-boot-starter-web, spring-boot-starter-thymeleaf, and spring-boot-starter-actuator.

This article describes some reusable code targeted for development and testing (a REST controller @ /jig/bean/{name}.json and /jig/bean/{name}.xml) and the steps necessary to create a Spring Boot starter. It also describes a starter for the embedded MySQL server process described in “Spring Embedded MySQL Server”.

Jul 19, 2020

Java Multi-Release JARs

“Adding Support to Java InvocationHandler Implementations for Interface Default Methods” describes how to implement an InvocationHandler to invoke default interface methods. This mechanism is critical to the FluentNode implementation described in “Java Interface Facades”. The first article also notes that the MethodHandles.Lookup method used with Java 8 would not work with Java 9 which means the whole API will not work on Java 9 and subsequent JVMs.

This article describes the Java 9-specific solution, refactoring the InvocationHandler implementation to separate and compartmentalize the Java 8 and Java 9-specific solution logic, and introduces “JEP 238: Multi-Release JAR Files” to deliver a Java 8 and Java 9 (and later) solutions simultaneously in the same JAR.

Jun 26, 2020

Spring Boot Part 5: voyeur, A Non-Trivial Application

This series of articles examines Spring Boot features. This fifth article in the series presents a non-trivial application which probes local hosts (with the help of the nmap command) to assist in developing UPNP and SSDP applications.

Jun 17, 2020

Java Stream Tree Walker

This article discusses walking a tree or graph of nodes with a Java 8 Stream implementation. The implementation is codified in a Spliterator The strategy described herein can be a useful alternative to implementing a class-hierarchy specific visitor because only a single per-type method need be defined (often as a Java lambda).

Mar 16, 2020

AWS VPC Set-Up with Ansible

A critical first step to creating an Amazon Web Services (AWS) AWS Elastic Compute Cloud (EC2) configuration is to configure a Virtual Private Cloud (VPC) Often, the default configuration is sufficient for most administrators’ needs but some solutions require an IP address space different than the Amazon default. This article presents the Ansible boilerplate for configuring an alternative IP address space specified by a minimum of parameters: region, VPC CIDR block (e.g., and subnet mask size (e.g., 20). The boilerplate calculates subnet CIDR blocks (e.g.,,, etc…) for each availability zone within the region.

Mar 15, 2020

CentOS In-Place Upgrade

CentOS 8.0 was released on September 24th, 2019 and 8.1 on January 15, 2020. This article describes how a CentOS 7 may be upgraded in place.

Jan 1, 2020

Spring Boot Part 4: Spring MVC with Thymeleaf

This series of articles will examine Spring Boot features. This fourth installment discusses Spring MVC, templating in Spring, and creates a simple internationalized clock application as an example. The clock application will allow the user to select Locale and TimeZone.

Dec 15, 2019

Spring Boot Part 3: Dependency Injection and @RestController

This series of articles will examine Spring Boot features. This third article builds on the series by demonstrating the basics of Spring Dependency Injection. To create demonstrable code the example also creates a @RestController implementation, a simple shared property server where clients may put and get property values.

Nov 17, 2019

Spring Boot Part 2: Static Resources

This series of articles will examine Spring Boot features. This second article builds on the first article by demonstrating how to serve static resources from the classpath and WebJars.

Nov 16, 2019

Spring Boot Part 1: Minimum Web Server, Devtools, and Actuator

This series of articles will examine Spring Boot features. This first article will look at the minimum Spring Boot application, Spring Boot Devtools, and the Spring Boot Actuator. There are already a wealth of resources for Spring Boot including the Spring Initializr; these articles do not intend to replace these resources but instead provide a collection of skeletal projects which may be quickly and easily used to experiment with specific Spring Boot features.

Oct 19, 2019

Spring Embedded MySQL Server

This article describes a method to create a mysqld Process managed by the Spring Boot Application conditioned on the definition of an application.properties property, ${mysqld.home}.

Sep 15, 2019

Maven toolchains.xml Script

Apache Maven has introduced Maven Toolchains to ease configuring plug-ins and to avoid specifying any JDK location in the project POMs. Available JDKs are configured in ${HOME}/.m2/toolchains.xml. This article introduces a script to automate the generation of the toolchains.xml file, toolchains.xml.bash.

Jul 8, 2019

FiveThirtyEight "What’s Your Best Scrabble String?" Solution

FiveThirtyEight presented a challenge to order Scrabble tiles to generate the largest score.

Jun 3, 2019

Spring PasswordEncoder Implementation

Spring Security provides multiple PasswordEncoder implementations with BCRYPT as the recommended implementation. However, the use-case of sharing an authentication database with an external application, Dovecot, is examined in this article.

Mar 30, 2019

Java Interface Facades

This article discusses extending final implementation classes through the use of Proxy InvocationHandlers and Default Interface Methods introduced in Java 8. The specific use case described here is to add fluent methods to Document Object Model (DOM) to enable Javadoc implementations to provide snippets of well-formed HTML/XML.

Mar 28, 2019

Java Streams and Spliterators

This article discusses implementing Java 8 Streams and the underlying Spliterator implementation. The nontrivial implementations described here are Permutations and Combinations streams, both of which provide a stream of List<T> instances representing the combinations of the argument Collection<T>.

Jan 31, 2019

Adding Support to Java InvocationHandler Implementations for Interface Default Methods

Java 8 introduced default methods to interfaces. Existing InvocationHandler implementations will not invoke default interface methods. This short article documents the necessary changes.

Jan 30, 2019

A java.net.ResponseCache Implementation

The Java URLConnection mechanism may be configured to use a ResponseCache. This article describes a ResponseCache implementation.

Dec 18, 2018

Google Cloud Platform App Engine Deployment Experience

This article describes some of the challenges and pecularities of deploying an annotated @SpringBootApplication application to Google Cloud Platform.

Aug 22, 2018

AWS EC2 User Data Shell Script

Creators of Amazon Elastic Compute Cloud (EC2) instances may stuff a script into the “user data” which will be executed on the instance’s initial boot. This script may be useful to mount Elastic Block Store (EBS) volumes as file systems since those volumes cannot be attached to the instance until after the instance has been created and started.

This article presents a script which leverages the functions provided in the aws.rc script described in a previous article.

Aug 20, 2018

automount/autofs Executable Map for Amazon EBS Volumes

Amazon Web Services (AWS) provides their Elastic Block Store (EBS) service for persistent block storage for Amazon Elastic Compute Cloud (EC2) instances in the AWS cloud. Linux/UNIX file systems may be created on these volumes and then attached to an instance and subsequently mounted as a file system. However, the EC2 instance must be started before the volume can be attached which may lead to significant challenges in architecture design as both the numbers of instances and volumes increase.

This article presents an implementation of an executable automount map which may be leveraged to attach and mount EBS volumes on demand. The implementation includes a mechanism for detaching unmounted EBS volumes so they me be attached to different instances in the future.

Aug 6, 2018

Ghost Theme and Site Development

This is the inaugural post to this blog. Specifically, this post documents setting up this blog.