fidzu : Java

Running Apache Flink on a mainframe sounds odd at first. A modern stream processing engine on a platform most people call legacy? But take a closer look. It is not only possible. It might be a smart move for some of the largest financial institutions in the world. This post explores why some enterprises want Apache Flink on the mainframe, how it could work, and whether it is a brilliant innovation or a technical detour.

Disclaimer: The views and opinions expressed in this blog are strictly my own and do not necessarily reflect the official policy or position of my employer.

10 Sep 2026 7:00pm GMT

If you ask Java developers about the concept of 'Sneaky Throws,' I am almost sure there will be a couple of opinions that are quite differently expressed, but similar in their meaning. Some will sum it up as being able to throw checked exceptions without declaring them explicitly; others will amend that it means writing functional-style code (lambdas) and being allowed to call methods that throw checked exceptions.

Most probably, it will be surely mentioned that there's a Lombok annotation called exactly @SneakyThrows that solves the problem immediately when put on a method. Last but not least, to outline it in a more pragmatic manner, the concept allows tricking the Java compiler into treating checked exceptions as runtime exceptions.

10 Sep 2026 6:00pm GMT

In a previous article, Working with Spreadsheets in Java: A Practical Overview, we walked through the common scenarios where Java applications need to interact with spreadsheets and the categories of tools available for the job. One of the factors mentioned there was support for modern Excel formulas - a topic that deserves more space than a single bullet point.

Java applications interact with Excel more often than most teams plan for: file uploads from finance, calculation logic authored in a workbook, reporting exports back to business users. The files these users produce today are not the same as the files they produced five years ago. Excel 365 and Excel 2021 introduced a new formula model, and workbooks authored in those versions routinely use it. Depending on which library you use, those formulas may evaluate correctly, fail silently with stale cached values, or throw exceptions at recalculation time.

09 Sep 2026 2:00pm GMT

A pull request arrives. A few hundred lines of Java implementing the new discount rule: tiered thresholds, a regional exception, something about loyalty tiers that nobody can quite explain. It compiles. The tests pass. An LLM wrote it in about forty seconds.

Now: who reviews it?

04 Sep 2026 2:00pm GMT

Every Java developer who runs services on Kubernetes has watched this scene play out. Traffic spikes, the autoscaler adds a pod, and then everyone waits. The container is running in two seconds. The application is not ready for another twelve seconds. During those ten seconds, your existing pods absorb the extra load, latency climbs, and if things are bad enough, the autoscaler panics and adds even more pods that are also not ready.

I spent years treating Spring Boot startup time as a fact of life, the way you treat weather. Then I found out the JVM has had a fix for a big chunk of it since Java 12; it works beautifully inside Docker, and almost nobody bakes it into their images. It is called Class Data Sharing, CDS for short, and this article shows you how to make your Docker build do the work

03 Sep 2026 6:00pm GMT

Any input/output operation, be it accessing a file, handling an HTTP request, or a database connection, is based on 3 fundamental system concepts - file descriptors, kernel memory, and heap size.

This article discusses how modern languages help developers handle behind-the-scenes file descriptor, kernel memory, and heap management. These three concepts are major bottlenecks for scaling.

03 Sep 2026 4:00pm GMT

"...premature optimization is the root of all evil…"

Donald Ervin Knuth

28 Aug 2026 5:00pm GMT

In a chapter of The SingleStore Cookbook, there is a complete sentiment analysis pipeline using Rust compiled to WebAssembly and loaded directly into SingleStore via its Code Engine. The result was clean: one CLI command to deploy, sentiment scoring running inside the database engine alongside the data and a full stock-price-plus-headlines analytical pipeline built on top of it.

Can we do the same thing in Neo4j?

27 Aug 2026 2:00pm GMT

Goose - the open-source, Rust-based AI developer agent from Block (donated to the Linux Foundation's Agentic AI Foundation) - interacts natively with your local development environment via the Model Context Protocol (MCP). In this tutorial, you will learn how to build stateless, cloud-native Java microservices using Quarkus LangChain4j and expose them as governed MCP extensions that Goose can discover and run seamlessly.

Autonomous AI coding agents like Goose go far beyond simple code autocompletion. Built in Rust for speed and portability, Goose runs on your local machine, inspects files, runs terminal commands, and uses tools over MCP to automate complex engineering tasks.

26 Aug 2026 6:00pm GMT

Java Meets the Spreadsheet

Apache POI has been the standard Java library for reading and writing Excel files for over twenty years. It handles the majority of everyday spreadsheet tasks well. But a growing category of real-world Excel files now contains formulas that POI's evaluator cannot execute at all.

This is one of several situations Java developers hit when working with spreadsheets that are not obvious until you are already in production. Business users produce, share, and reason about data in spreadsheets. Finance teams model in Excel. Operations teams track inventory in Excel. Analysts hand deliverables to engineering as .xlsx files. Java applications end up interacting with all of it: back-office services accept Excel uploads, pricing engines run calculations that were originally authored in a workbook, reporting tools export data in a format the recipient can open in Excel without formatting problems.

26 Aug 2026 3:00pm GMT

Scaling JMS Listeners With Java Virtual Threads

Event-driven architecture is widely used in enterprise systems to decouple services, absorb traffic spikes, and move work out of request paths. Java Message Service (JMS), now standardized as Jakarta Messaging, remains common in systems built around ActiveMQ, IBM MQ, Solace, TIBCO EMS, and similar brokers.

Java 21 virtual threads give these systems another scaling option. A JMS listener often spends more time waiting on a database, HTTP service, cache, or file system than it spends using the CPU. Moving that blocking work to virtual threads can reduce platform-thread pressure without forcing the application into a reactive programming model.

21 Aug 2026 4:00pm GMT

Artificial intelligence is changing software engineering, impacting automation, user interaction, data analysis, and application development. Developers are evaluating how their technology stacks fit with these changes. For Java developers in enterprise settings, a main question is whether the Java enterprise ecosystem is prepared for AI.

The short answer is yes. You do not need to abandon Java or wait for a new platform to build AI-enabled applications. Java already provides a mature ecosystem of AI libraries, model providers, APIs, and integration patterns. Jakarta EE offers the capabilities required to deploy these technologies in production-grade enterprise systems today.

18 Aug 2026 5:00pm GMT

The Problem: Our p99 Was 3-5 Seconds

Our PyFlink pipeline was missing its latency SLO by seconds. The pipeline itself was straightforward: consume events from Kafka, transform them, serialize them as Protobuf, and write the results to downstream systems. Yet under production load, p99 end-to-end latency was consistently in the 3-5 second range.

Profiling pointed us to an unexpected bottleneck: we were deserializing Protobuf messages in Python, even though the Flink runtime processing our stream was JVM-based. Every record that entered the Python path had to cross the JVM-to-Python process boundary, get parsed by a Python UDF, and then cross back. The business logic wasn't the problem. The doorway was.

07 Aug 2026 4:00pm GMT

Building autonomous AI agents with large language models (LLMs) is easy when writing single-turn demo scripts. However, moving multi-agent loops into production introduces serious architectural challenges. Agents hallucinate, loop infinitely without reaching convergence, require human approval for high-risk operations, and need standard tool-calling integrations alongside clear operational governance.

Historically, Java developers faced a tough choice: either rely on heavyweight, external workflow clusters (like Temporal or Camunda) that add operational overhead, or hand-craft fragile while loops and custom state machines inside their services.

07 Aug 2026 3:00pm GMT

Then the search form grows, filters multiply, and nested criteria appear. Since using GET means placing the query inside the URI, a length limit problem emerges. Worse, placing sensitive query values in the URI increases the chance of exposure through access logs, browser history, proxies, and monitoring systems. Because the HTTP protocol does not forbid it, sending a body with GET may look like a way out, but building your design on behavior the standards leave undefined is not a recommended practice. Elasticsearch's GET-with-body search API is a well-known example, and Elastic's own documentation openly acknowledges the problem:

"As a result, some HTTP servers allow it, and some-especially caching proxies-don't. [...] However, because GET with a request body is not universally supported, the search API also accepts POST requests."

06 Aug 2026 5:00pm GMT

Every Java developer knows the ritual. A JAVA_HOME export in one profile file, a different one in another. sdk use java 21 in this terminal, but the other terminal is still on 8. The build passes in your shell and fails in the IDE because the IDE launched from the dock and never sourced your init line. A teammate's "works on my machine" that turns out to mean "works on my shell."

I got tired of it, so I built Jolta. It's Volta, but for Java. This article is partly about what it does, but mostly about how I built it, because the process is the part I'd recommend to anyone building in a crowded tool category: I mined my competitors' bug trackers and turned their backlogs into my test suite.

04 Aug 2026 5:00pm GMT