One of the shortcomings of the previous solution is that we are yet unable to select a provided service based on non-functional characteristics. As a user, I do not care if the chosen string matcher follows the design of the Knuth-Morris-Pratt or the Boyer-Moore algorithm. Instead, I want it to be stable and fast. If there is a new, but yet not thoroughly tested matcher available, I may want to use that for an experimental client. When we think in terms of suitable implementations for the problem we try to solve, we do not think about implementation internals at first, but rather about the non-functional requirements that govern the process of finding a suitable solution.

Although we progressed through to a working, modularized solution for our string matchers during the last article, we still have an unwanted dependency that goes directly from module matchers.cli to matchers.impl. This prohibits us from using a clean and extensible way of injecting implementations of the Matcher interface. Working through this article, our goal is to end up with a very loose coupling between our Java modules by implementing a mechanism for that kind of dependency injection.

During the course of this article we will migrate an existing Java 8 application to a fully modularized Java 9 application that leverages the capabilities of the Java Platform Module System (JPMS). This article is the first installment of a series of articles that showcases a migration path towards a loosely coupled and modularized application architecture.