Stream[Article]: 2017

Verifying End-to-end Test Code Coverage using Jacoco Agent

Fact - End-to-end tests are critical if you want to make sure your software works as it should. To be 100% sure that you covered every (or almost every) possible branch in your business code, it is worth to check what code has been invoked after your E2E suite finished successfully. The solution I am going to present may be much easier, if you are able to stand up your application locally. Sometimes though, it is not the case.

In this scenario, we are going to start two instances of some web application at the remote servers, with code invocation recording turned on. Next, we are going to run integration test pointing to them one after another with different parameters, to test different paths.

Jul

Lifting functions to work with monads in Java

Functional Programming in Java

Stream and Optional classes - added to Java 8 - allow you to have some fun with functional programming. The problem is Java still misses quite a lot to be taken as a serious FP language. Lambda notation and two monads (Optional and Stream) are just the tip of the iceberg. This leads to arising of libraries like vavr or functionaljava - both deriving from purely functional language Haskell.

Jul

Composing functions with java.util.function.Function.andThen() trick

In this article, I am going to present you a simple trick that will make using java.util.function.Function.andThen() more useful.

As an example I will use ExternalSystemGateway class, which job is to call external system along with serializing/mapping the messages:

You can see that every line of the invoke method does some kind of action, which transforms some input type to another output type.

Jul

Exception-free code using functional approach

Checked exceptions & Java 8

Defining custom exceptions (both checked and unchecked) is a common approach to handling errors in Java applications. It usually leads to creating a new class for every different type of error, marking methods with throws keyword or wrapping code with try-catch blocks. This can lead to the code which is hard to read since every block adds another level of complexity.

Lambdas in Java 8 started the boom for functional approach in writing the code.