Java Web Development (JSP/Servlets) Services

This article is part of the series “Stranger things in Java,” dedicated to language deep dives that will help us master even the strangest scenarios that can arise when we program. All articles are inspired by content from the book “Java for Aliens” (in English), the book “Il nuovo Java”, and the book “Programmazione Java.”

This article is a short tutorial on enumeration types, also called enumerations or enums. They are one of the fundamental constructs of the Java language, alongside classes, interfaces, annotations, and records. They are particularly useful to represent sets of known and unchangeable values, such as the days of the week or the cardinal directions.

When designing a Java library, extensibility is often a key requirement, especially in the later phases of a project. Library authors want to allow users to add custom behavior or provide their own implementations without modifying the core codebase. Java addresses this need with the Service Loader API, a built-in mechanism for discovering and loading implementations of a given interface at runtime.

Service Loader enables a clean separation between the Application Programming Interface (API) and its implementation, making it a solid choice for plugin-like architectures and Service Provider Interfaces (SPI). In this post, we’ll look at how Service Loader can be used in practice, along with its advantages and limitations when building extensible Java libraries.

Major version upgrades of search infrastructure are often treated as dependency and configuration exercises. In practice, when search sits upstream of machine-learning pipelines and directly impacts revenue, such upgrades can fail in far more subtle — and harder to diagnose — ways.

This article describes how a long-stalled migration of a production ads retrieval system from Apache Solr/Apache Lucene 5 to 8 was unblocked after multiple prior attempts had failed. The failures were not caused by missing dependencies or misconfiguration, but by cumulative semantic drift and execution-path changes that only manifested under real production conditions.

Point-of-Sale (POS) systems are no longer just cash registers. They are becoming real-time, connected platforms that handle payments, manage inventory, personalize customer experiences, and feed business intelligence. Small and medium-sized merchants can now access capabilities once reserved for enterprise retailers. Mobile payment platforms like Square, SumUp, and Shopify make it easy to sell anywhere and integrate sales channels seamlessly.

At the same time, data streaming technologies such as Apache Kafka and Apache Flink are transforming retail operations. They enable instant insights and automated actions across every store, website, and supply chain partner.