A Java geek

Security Baked Into the JVM: two Subjects, one call

The constraint system stops a bad call before it leaves the JVM. The Safe Codebase Audit Pipeline stops bad code before a client ever loads it. What remains is identity: who is calling, and can you verify it? Most frameworks answer with a token check at the door. A filter validates a bearer token, sets a thread-local variable, and hopes that nothing downstream forgets to look at it. DirtyChai answers differently.

Technical

GitHub agentic workflows and Renovate

I’ve been a big fan of Renovate for a couple of years already. Renovate scans your repositories, detects outdated package versions, and opens pull requests to automatically bump them. It’s similar to Dependabot in that it keeps your dependencies up to date. If I had to compare them in one sentence, I’d say Renovate is less integrated in the GitHub ecosystem, but handles more ecosystems and, more importantly, is extensible.

Development

RFC 9880 and the IoT Validation Problem

The IoT/IIoT world has a data model problem and the concept of Digital Twin has made this issue more important. Plenty of people have tried to fix it. RFC 9880 and its Semantic Definition Format (SDF) are a serious attempt: a JSON-based, ecosystem-neutral way to describe what a device is and what it does. I have had some experiences with this specification, and I’ve understood that the format shows its full value once you treat it as source code, something you compile.

Technical

Security Baked Into the JVM: the Safe Codebase Audit Pipeline

In Part 1, the minimal deployment showed constraints traveling with the proxy: authentication, encryption, hardened deserialization, all declared in configuration and enforced at the call boundary. The proxy is a JAR. That JAR was downloaded and unmarshalled before any constraint ran. That step is the earlier problem. Distributed Java systems that load remote code are vulnerable to supply chain compromise: an attacker can replace a legitimate JAR with one containing malicious bytecode.

Java

Making ServiceLoader usable: a provider factory

I keep coming back to java.util.ServiceLoader. I have used it to put a JSON layer behind a contract, so the core code carries no direct dependency on any particular JSON library, and I can swap the implementation without touching callers. The same shape works for JWT handling, where the concrete library might be jose4j or another JOSE implementation, and you can easily find other decoupling use-cases.

Technical

Two nasty surprises in Home Assistant's config

Last year, I motorized the rolling shutters on the southern façade of my apartment. My idea was to manage them via Home Assistant. I had a couple of automations in mind: In the evening, roll down the shutters of my bedroomIn the morning:If it’s too hot outside, roll down all shuttersIf it’s too cold outside, roll down all shuttersIn other cases, roll up all shutters but my bedroom’s Living in France, I added the official Météo France integration.

Technical

Security Baked Into the JVM: why fork Apache River and OpenJDK?

The more distributed a system, the harder it is to secure. Code crosses JVM boundaries. Objects are serialized across trust boundaries. Third-party proxies run inside your process. The usual answer is a network firewall. It helps, but it operates at the wrong level. Java 17 deprecated the SecurityManager, Java 24 put the final nail in its coffin. Most developers didn’t notice.

Development

On programming languages, targets, and platforms

I started as a Java developer, but for some time now, I have broadened my horizons. Recently, I thought about how early languages were dedicated to a single target and platform, and now they are broadening their focus. In this post, I want to write down my thoughts in the hope that it may be useful to others, probably to my future self. Definitions You may have been wondering about the title terms.

Java

double, BigDecimal, or Fixed-Point?

There is an evergreen debate in the Java world: should you always use BigDecimal for money? The short answer is no. The real answer is: it depends on your computational context: the precision you need, the rounding rules you must follow, and the performance budget you have. The problem is that this conversation is often driven by dogma rather than engineering.

A Java geek

Nicolas Fränkel's blog