Scientist4J

A port of Github's refactoring tool Scientist in Java

Installation

<dependency>
    <groupId>com.github.rawls238</groupId>
    <artifactId>Scientist4JCore</artifactId>
    <version>0.7</version>
</dependency>

Usage

This Java port supports most of the functionality of the original Scientist library in Ruby, however its interface is a bit different.

The core component of this library is the Experiment<T> class. It's recommended to use this class as a Singleton. The main usage is as follows:

Basic Usage

You can either run a synchronous experiment or an asynchronous experiment.

For a synchronous experiment, the order in which control and candidate functions are run is randomized.

To run a synchronous experiment:

Experiment<Integer> e = new Experiment("foo");
e.run(this::controlFunction, this::candidateFunction);

For an asynchronous experiment, the two functions are run asynchronously.

To run an asynchronous experiment:

Experiment<Integer> e = new Experiment("foo");
e.runAsync(this::controlFunction, this::candidateFunction);

Behind the scenes the following occurs in both cases:

It decides whether or not to run the candidate function
Measures the durations of all behaviors
Compares the result of the two
Swallows (but records) any exceptions raised by the candidate
Publishes all this information.

Dropwizard

Out of the box this uses Dropwizard metrics to report the following stats. The following metrics are reported which have the form scientist.[experiment name].*:

duration of default behavior in ms
duration of candidate behavior in ms
counter of total number of users going through the codepath
counter of number of mismatches
counter of candidate exceptions

You can provide your own metric registry object/bean via the constructor or by extending the Experiment class and overriding the getMetrics method.

Optional Configuration

Users can optionally override the following functions:

publish (to publish results of an experiment if you don't want to use the default Dropwizard metrics)
compareResults (by default this library just uses equals between objects for equality, but in case you want to special case equality between objects)
enabled (to limit what % of users get exposed to the new code path - by default it's 100%)
runIf (to enforce conditional behavior on who should be exposed to the new code path)
isAsync (force using the async for legacy code or move to runAsync method)