Engineering notes
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ArrayList vs LinkedList: The Numbers Behind the Table
Everyone knows the complexity table. Here is what each operation actually costs when you time it — including the one result that contradicts the folklore.
JavaHow to Run a Spring Boot App as a Linux Service (and How Small a Box It Needs)
The systemd unit file for a Spring Boot jar, the one line most of them are missing, and measured answers to how much memory the thing actually uses.
Cloud & DevOpsHow to Dockerize a Spring Boot Application, and What Each Choice Costs
Four images built from one Spring Boot app, measured — 785MB down to 531MB, and why the layered build that everyone recommends does not shrink anything.
ContainersHow to Secure a Spring Boot API with JWT (Without Writing a Filter)
Spring Security already parses and validates JWTs. Here is the whole setup — two beans and one line of DSL — plus what a short example quietly defers.
Backend & APIsHow to Build a REST API in Spring Boot, Including the Failures
Build a working Spring Boot REST API — GET, POST, 201 with Location — then see what your callers actually get back when the request is wrong, and fix it.
Backend & APIsHow to Create a Spring Boot Project (and What the Generator Actually Gives You)
Create a Spring Boot project with Spring Initializr, then read every one of the ten files it writes — and find out what the 19 MB jar you build actually holds.
Backend & APIsHow to Set the JAVA_HOME Environment Variable on Windows, Linux, and macOS
Set JAVA_HOME correctly on Windows, Linux and macOS — find the JDK folder, make the variable stick across reboots, and fix the errors it causes.
JavaDifference Between JDK, JRE and JVM: What Each One Actually Does
JDK, JRE and JVM explained by following one file from javac to output: what each layer holds, why Oracle stopped shipping a JRE, and which one to install.
JavaMySQL vs PostgreSQL: The Differences That Actually Matter
A concrete comparison of MySQL and PostgreSQL: MVCC and VACUUM, clustered index vs heap, isolation defaults, transactional DDL, and replication durability.
Databases