security Attach API JMX JConsole

Beware the Attach API

A post brought to light an interesting feature of the JDK I didn’t know about: the ability to update a code running in a JVM. The referenced post shows how to apply a bugfix using that feature. The devious white hat JVM hacker in me started to think how one could apply that trick for other less beneficial purposes. And of course, how to prevent that. Hack overview Let’s imagine a banking application based on the familiar Spring Boot stack. A TransferService class is dedicated to

Kotlin collection sequence stream lazy evaluation

Kotlin, collections and sequences

When streams were added to Java 8, I wanted to jump on the bandwagon. I read blog posts, watched videos, attended workshops to understand what this was all about. After a while, I became comfortable enough…​ but I was unhappy with the implementation: while streams offer methods with a functional approach, legacy collections do not. When one wants to use Java capabilities on an existing collection, the later needs to be transformed to a stream, and then back again. For example, the f

Clojure sequence stream

Feedback on Learning Clojure: comparing with Java streams

Coming from a Java background, I'm currently trying to learn the Clojure programming language, with the help of online resources and mentorship. Some weeks ago, I tried to wire things together by trying to find equivalent methods to those available in Java streams. While I managed to get things working, writing working code and writing idiomatic code are two very different things. I was fortunate to have a good degree of feedback from different sources: Hacker News, Reddit and on this very blog.

builder design pattern state machine

The Builder pattern is a finite state machine!

Some weeks ago, I read the post referenced in a tweet. In short, the article provides two ways to generate the boilerplate code required by the Builder pattern: Lombok, to generate code at compile time and the Spark Eclipse plugin, to generate code at development time. However, I already wrote about the Builder pattern. And it's a bit more complex than what's described in the referenced post.

annotations reflection vaadin

Listing annotated classes in Java EE

The Java EE platform is huge, and I must confess I'm not aware of every one of its API. This is also true of the Spring framework, even though I think I know more of Spring than of Java EE. Lately, I was working on the version 10 of the Vaadin framework also known as Vaadin Flow. This version introduces routes. When a path is requested, the Vaadin Servlet displays the component. Routes are created by annotating specific components with the @Route annotation. Thus, Vaadin needs to list all annotat

API JDK design Cloneable

Cloneable, a Java design gotcha

Some time ago, I described a couple of surprising design choices in the JDK functional interfaces API. Lately, during a lesson, a student of mine proposed to shallow-copy an ArrayList by using the clone() method: I thought this is another API gotcha worth writing about. Cloning an object means a new object is created with the same state as the original one. As per the JavaDoc: Creates and returns a copy of this object. The precise meaning of 'copy' may depend on the class of the object.

Clojure arrow threading

Learning Clojure: the arrow and doto macros

For me, learning a new language is like getting into the sea: one toe at a time. Last week was the occasion to get familiar with the spec library. This week, we will have a look at some powerful macros. The problem When you’re not used to Clojure, parentheses may sometimes impair the readability of code. (- 25 (+ 5 (* 3 (- 5 (/ 12 4))))) The Kotlin equivalent of the above snippet would be: 25 - (5 + (3 * (5 - (12 / 4)))) Obviously, it’s related neither to Clojure nor