BlockHound VS initializr

There is a great tool called Blockhound we can use to detect if/when we have a blocking call in our application. This way, we can ensure that we don't break the non-blocking nature of our application by mistake while developing new features. Setting it up is fairly straightforward.

There's even a test library to detect them: https://github.com/reactor/BlockHound

One of the talks in my current portfolio is Migrating from Imperative to Reactive. The talk is based on a demo migrating from Spring WebMVC to Spring WebFlux in a step-by-step approach. One of the steps involves installing BlockHound: it allows to check whether a blocking call occurs in a thread it shouldn't happen and throws an exception at runtime when it happens.

The first step is to make the application compatible with GraalVM. We need to remove Blockhound from the code. Blockhound allows verifying that no blocking code runs in unwanted places. It's a Java agent that requires a JDK, not a JRE. It's great for a demo, but it has nothing to do with a production application.

The best way, for generating a ready-to-run application in Java you can use the Spring Boot Initializr tool.

curl --location 'https://start.spring.io/starter.zip?type=maven-project&language=java&bootVersion=3.2.2&baseDir=ms-xcoffee&groupId=com.xcoffee&artifactId=ms-xcoffee&name=ms-xcoffee&description=Demo%20project%20for%20Spring%20Boot&packageName=com.xcoffee.ms-xcoffee&packaging=jar&javaVersion=21&dependencies=webflux%2Clombok%2Cvalidation' | tar -xzvf -

In this segment we will create a basic Spring boot app from Spring Initializer. Add the below dependencies:

Add the following MongoDB dependencies in your pom.xml or use spring initializer and select the Spring Data MongoDB dependency:

I created all of these applications using start.spring.io's REST API and HTTPie.

An easy way to create the skeleton project is to visit Spring Initializr, I set the Project to Gradle - Groovy, Language to Java, and add Spring Web dependency. Then it's just to generate the project and unpack it.

Create a new Spring Boot application using the Spring Initializr. You can use the web version or the curl command below. Use the default for most of the options. For the dependencies, select web, and okta. For the build tool, select Gradle.

I will start with a simple example of a cloud function, which is the same as a rest endpoint in the classical spring boot web application. You can create a project from your favorite IDE or from Spring Initliazr.