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I’m an independent IT consultant and entrepreneur in the Internet and software business. I’m interested in design, enterprise applications, web apps and SaaS products. I design and develop business solutions and applications. I help companies in terms of software quality and knowledge transfer, e.g. with Angular and Spring Boot.

Inversion of Control vs Dependency Injection

Dependency injection is one way of implementing inversion of control - a programming principle that allows for better modularity and extensibility. Dependency injection is commonly achieved via constructor injection, field injection, or setter injection. Inversion of control is an abstract concept, which dependency injection is a realisation of. Other methods of implementing inversion of control for example include the template pattern, service discovery, delegates, events, and currying (when applying a functional programming paradigm). Read more

A Catalogue of Design Patterns

Recently, I came across this well-structured as well as visually appealing catalogue of software design patterns on Refactoring.Guru. The subject of design patterns can be a somewhat dry, unwieldy one. Hence, using visuals and metaphors can come in handy when explaining both the general idea behind design patterns and specific patterns alongside with their use cases. Refactoring.Guru does a great job not only at explaining the origin and purpose of and rationale behind design patterns and pattern languages but also at describing each ... Read more

Cloud Design Patterns

In the past few months, I've been working a lot with distributed applications and more complex cloud architectures, both in terms of Stratospheric - From Zero to Production with Spring Boot and AWS (the eBook I'm currently writing together with Tom Hombergs and Philip Riecks) and client work. Microsoft's library of Cloud Design Patterns (as previously mentioned in this blog post) is a collection of cloud-related software and infrastructure design patterns that can help you with weighing up the merits of common ... Read more

Push Notifications with Amazon MQ – Sample From “Stratospheric – From Zero to Production with Spring Boot and AWS”

The following is an excerpt from the chapter on "Push Notifications with Amazon MQ" from the eBook "Stratospheric – From Zero to Production with Spring Boot and AWS" I'm currently writing together with Tom Hombergs and Philip Riecks. You can get the eBook over at Leanpub. Push Notifications With Amazon MQ As discussed in the chapter "Sharing Todos with SQS and SES" we might want to share our Todos with others. Being able to share Todos is already quite helpful for working on tasks ... Read more

CORS: What It Is and How It Works

Expanding on last week's article on best practices for REST API Design I'd like to point to a specific aspect working REST APIs frequently entails: A browser security feature called "Cross-Origin Resource Sharing (CORS)". This feature allows you to define which resources provided by a web application are supposed to be accessible from which origin, which in turn typically is comprised of protocol, host / domain name and port. This website's origin for example is https://bjoernkw.com:80 (port 80 is the default port ... Read more

REST API Design: Best Practices

It's probably safe to say that REST (REpresentational State Transfer - originally described by Roy Fielding) is the most widely used architectural pattern when it comes to APIs in web application contexts. From statelessness, to self-descriptive messages, and hypermedia as the engine of application state (HATEOAS) REST comes with quite a few principles, constraints, patterns, and flavours, not all of which are used or applied consistently with each REST API. REST often is a rather loosely-applied architectural pattern or a continuum, on ... Read more

Five Articles on Software Quality and Design Patterns

This week I'd like to point you to five articles I previously posted on this blog and from which I think that they're as relevant as they were at the time. The first three are about general software design principles, software architecture and software quality while the final two refer to specific best practices and common design patterns for Angular: Writing Disposable Code, Not Reusable Code (November 06, 2016) What Causes Over-engineering and How Can You Prevent It? (April 16, 2017) Less Is More ... Read more

The Mother of All Leaky Abstractions: The 500-mile Email

In last week's musings I complained about leaky abstraction on two counts, which reminded me of what in my opinion must be the mother of all leaky abstractions: The notorious 500-mile email. Impedance mismatches and TCP connections seeping through the cracks of the latest reactive programming frameworks certainly at times are difficult to deal with but the actual underlying transmission protocol of the relativistic universe shining through when trying to send an email? It can't get any better than that ... Read more

Monoliths Aren’t Inherently Bad

Self-professed minimalist developer Kelsey Hightower a few months ago wrote about monoliths being the future. The microservice design pattern has been trending in software development for quite some now. Unfortunately, more often than not it's been indiscriminately treated as a panacea to every software architecture and design problem out there. Microservices can help with one aspect specifically: Reducing deployment risk. If you have a large monolith and frequently need to make changes to a specific part or feature provided by that monolith the whole ... Read more

The Richardson Maturity Model for REST APIs

On his website about software design patterns Martin Fowler provides an in-depth explanation of the Richardson Maturity Model for HTTP-based REST APIs by Leonard Richardson. According to that model REST APIs come in 4 levels of sophistication: Level 0, aka the "Everything is a POST request" model for example propagated by SOAP. This is basically tantamount to remote procedure invocation. Level 1 - Resources: Every resource is accessed through its own canonical URL. Level 2 - HTTP Verbs: Verbs such as GET, PUT, PATCH and ... Read more
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