Spring 5 WebFlux functional programming model

Spring 5 has the new module WebFlux to create reactive web applications. Spring WebFlux supports two programming models: traditional annotation-based programming model and functional programming model. In this post, we’ll going to scratch the surface of the new functional programming model. This post assumes that you already know concepts like Flux and Mono in Reactor.

We’ll use a calculator service as the example. This service supports operations like add, subtract, divide and multiply with two operands. The parameter operator specifies the operation to call, while parameters v1 and v2 specify the two operands. For example, the url /calculator?operator=add&v1=1&v2=2 invokes the add operation with values 1 and 2.

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Clean up disk space of Docker for Mac

After running Docker for Mac for a long time, Docker keeps eating up disk space. Even though the containers and images are removed, the disk space is not reclaimed. The problem is the file /Users/<username>/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2 is too big. For my Mac, this file is about 46G. This is actually a known issue tracked in this GitHub issue. So far, we only have a workaround to fix this issue.

Before applying this workaround, you should try docker system prune to remove unused data.

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JUnit 5 assumptions

Assertions verify that expected conditions are met after some executions. In some cases, the assertions may not even be necessary to run. This means that assertions can have assumptions. JUnit 5 provides static methods in the class org.junit.jupiter.api.Assumptions to describe test assumptions. When the assumption is not valid, the org.opentest4j.TestAbortedException is thrown and the test is aborted. There are three groups of static methods in Assumptions, assumeTrue, assumeFalse and assumingThat.

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JUnit 5 dynamic tests

In JUnit 5, we can create dynamic tests that are generated at runtime by factory methods. These methods are annotated with the annotation TestFactory.

The method annotated with @TestFactory must return a Stream, Collection, Iterable, or Iterator of DynamicNode objects. DynamicNode is abstract. It has two subclasses, DynamicContainer is the container of other DynamicNode objects; DynamicTest is a generated test case. DynamicTest is created from a display name and an Executable object. Executable is a functional interface that contains only one method void execute(). DynamicContainer is created from a display name and a collection of DynamicNodes.

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