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Large JSON responses with Jackson

Published on February 1, 2025

Jackson is the standard Object to JSON mapping library for Java. It converts POJOs to JSON strings and it parses JSON strings to populate POJOs. It sits behind many JSON based REST servers in Java including Spring MVC. For basic use cases it is very simple to use. Indeed, with Spring Boot it is completely transparent – the framework leverages Jackson to do Object to JSON mapping for you. It’s feature rich and extensible so it can usually handle more complex use cases too. One such use case is returning large JSON responses with Jackson.

Testing System.exit()

Published on October 30, 2022

Using JUnit for testing System.exit() calls from application code can be tricky. This is because System.exit() terminates the JVM running it. If you’re running JUnit, this is the JUnit runner. If JUnit invokes System.exit() in application code it will end your test without deciding a success / fail status and will also terminate the test run.

Scan a Redis Cluster

Published on July 30, 2022

The Redis SCAN command allows you to iterate over the key space. On a single Redis node you can SCAN all keys or just keys matching a pattern. It’s a slow operation: O(N) where N is the number of keys in the database. However, it can be useful when you want to view every item in the database or when there’s no way to find your values without traversing everything. Due to the way that Redis shards data though, it may be difficult to SCAN keys on a Redis Cluster. It is possible but it takes a little more work.

Testing Spring reactive WebClient

Published on January 15, 2022

Spring WebClient is the reactive replacement for the legacy RestTemplate. It has a more modern fluent API and first class support for Reactive Streams. This means it supports non-blocking, asynchronous responses.

However, the reactive WebClient does not yet have the mature test support that RestTemplate now has. There is not yet a standard recipe to test Spring WebClient applications. No doubt support will be improved in future versions but for now, here’s what works for me.

Securing a Zookeeper ensemble

Published on November 30, 2021

In the previous post, we looked at how to build a three cluster Zookeeper ensemble. However, the ensemble was not secured in any way. This would allow unauthorised clients to query Zookeeper and to push data to znodes. It also allows unauthorised Zookeeper instances to join the ensemble and potentially even instruct the cluster to shut down.

Even in secured networks, it’s a good idea to use some of the security features available in Zookeeper. In this post we’ll look at two security mechanisms: mutual TLS (mTLS) and SASL authentication. We’ll set up these security features on the server-server communication (leader election protocols) and client-server communication (Kafta to Zookeeper).

Building a Zookeeper ensemble

Published on October 28, 2021

Some notes on setting up and configuring a Zookeeper ensemble. Many guides use some shortcuts to setting up the ensemble such as running multiple Zookeeper instances on a single machine or running them in Docker. Both require some workarounds to make it work. As a better example, this guide runs three Zookeeper instances across three different VMs.

Microsoft Bot Framework Part 3: Connect to channels

Published on September 1, 2021

In the first two parts we built a bot using the Microsoft Bot Framework SDK and registered it in Azure. In this third and final part we’ll consume the bot using three of the available Bot Framework Channels: A simple chat component on a web page, SMS text and a fully custom Node.js application.

Microsoft Bot Framework Part 2: Build a bot with Bot Framework SDK

Published on August 7, 2021

The Microsoft Bot Framework is a flexible framework for building conversational bots. A bot can be written once and deployed to multiple channels including webchat, Microsoft Teams, Alexa and SMS. It supports text, speech and rich GUIs with images and controls.

In this three part series, I’ll register a ‘hello world’ bot application as an Azure Bot Resource and then look at how to customise my bot behaviours. Finally I’ll make it available to a chat widget on a web page, SMS and consume it from a Node.js application.

In the first part, we created an Azure Bot registration and connected to a demo bot application. In this part we’ll swap out the demo bot for one we’ve built using the Microsoft Bot Framework SDK.

Microsoft Bot Framework Part 1: Create an Azure Bot Resource

Published on July 27, 2021

In this part, I’ll register and configure a bot with Microsoft Azure Bot Service. It might seem odd to start here rather than going straight into the application code. However, getting this step out of the way gives us something simple to play with that works end to end.

Execute Around idiom in Java

Published on November 28, 2020

The Execute Around idiom is a pattern that allows you to wrap an action with some standard setup / tear down steps. Examples might include:

Execute within a lock: acquire the lock, do the action, release the lock
Resource handling: acquire the resource, do the action, close the resource
Execute as a user: switch to the user, do the action, switch back to the original user
Exception handling: do the action, handle the exceptions
Time an action: start a timer, do the action, stop the timer

The pattern allows you to pass in arbitrary actions and have them run with the same setup / tear down steps.

Category: How To