A few Java libraries have shown up recently that use text templates, but compile to Java classes at build time. They can thus claim to some extent to be "reflection free". Together with potential benefits of runtime performance, they promise to be easy to use and integrate with GraalVM native image compilation, so they are quite interesting for people just getting started with that stack in Spring Boot 3.x. We take a look at a selection of libraries (JStachio, Rocker, JTE and ManTL) and how to get them running. The source code for the samples is in GitHub and each template engine has its own…

Front end development these days is dominated by large JavaScript client side frameworks. There are plenty of good reasons for that, but it can be very inefficient for many use cases, and the framework engineering has become extremely complex. In this article, I want to explore a different approach, one that is more efficient and more flexible, built from smaller building blocks, and well-suited to server side application frameworks like Spring (or similar tools in a range of server side languages). The idea is to embrace the concept of hypermedia, imagine how a next-generation browser would…

Part 1 Plain Javascript with SSE Stream Vue isn’t really adding a lot of value in this simple HTML replacement use case, and it would add no value at all to the SSE example, so we will go ahead and implement that in vanilla Javascript. Here’s a stream tab: and some Javascript to populate it: Dynamic Content with React Most people who use React probably do more than just a bit of logic and end up with all of the layout and rendering in Javascript. You don’t have to do that, and it’s quite easy to use just a bit of React to get a feel for it. You could leave it at that and use it as a utility…

This article explores the different options that Spring Boot developers have for using Javascript and CSS on the client (browser) side of their application. Part of the plan is to explore some Javascript libraries that play well in the traditional server-side-rendered world of Spring web applications. Those libraries tend to have a light touch for the application developer, in the sense that they allow you to completely avoid Javascript, but still have nice a progressive "modern" UI. We also look at some more "pure" Javascript tools and frameworks. It’s kind of a spectrum, so as a TL;DR here…

If you have an application that connects to an RSocket server at runtime, how do you test it? We need a way for a test to start a server and tell us where it is listening, and then we need to be able to register request and response examples (a.k.a. "contracts"). That’s what this project provides - it’s like Wiremock but for RSocket. Getting Started The easiest way to use the project is as a JUnit (Jupiter) extension, e.g: With this extension installed the Spring Boot tests will run with an RSocket server listening on a port given by test.rsocket.server.port, so the test can connect directly…

Here's the latest graph of memory versus billing for Spring Cloud Function on AWS Lambda. It shows the billing metric GBsec as a function of memory allocation in Lambda for two custom runtimes, one in plain Java and one using a GraalVM native image, as described recently in this blog by Andy Clement: aws-billing-3.x In both cases the functionality is identical (a simple POJO-POJO function), and they both show only the results for cold start. Warm starts, where the function was already active when the request came in, were much faster and cheaper (except for the smallest memory setting they all…

Suppose you want to use Spring Boot, but you don’t want to @EnableAutoConfiguration. What should you do exactly? In an earlier article I showed that Spring is intrinsically fast and lightweight, but one of the short pieces of advice improve startup time was to consider manually importing the Spring Boot autoconfigurations, instead of sucking them all in automatically. It won’t be the right thing to do for all applications, but it might help, and it certainly won’t hurt to understand what the options are. In this piece we explore various ways of doing manual configuration and assess their…

Performance has always been one of the top priorities of the Spring Engineering team, and we are continually monitoring and responding to changes and to feedback. Some fairly intense and precise work has been done recently (in the last 2-3 years) and this article is here to help you to find the results of that work and to learn how to measure and improve performance in your own applications. The headline is that Spring Boot 2.1 and Spring 5.1 have some quite nice optimizations for startup time and heap usage. Here’s a graph made by measuring startup time for heap constrained apps: heap-size-…

Many people are using containers to wrap their Spring Boot applications, and building containers is not a simple thing to do. This is an article for developers of Spring Boot applications, and containers are not always a good abstraction for developers - they force you to learn about and think about very low level concerns - but you will on occasion be called on to create or use a container, so it pays to understand the building blocks. Here we aim to show you some of the choices you can make if you are faced with the prospect of needing to create your own container. We will assume that you…

Spring Cloud Function has a couple of new features in 2.0 (still in milestone phase), and possibly the most dramatic is the ability to go "fully functional". This is made possible by changes in Spring Boot 2.1 together with Spring Framework 5.1, and it means a different way of thinking about bean definitions in Spring applications, but also significant improvements in startup performance. AWS Cost Savings It’s always good to start with a picture, especially if it tells a story. Here’s a graph that shows the improvement in Spring Cloud Function 2.0 over 1.0, comparing the cost of cold starts in…