recent posts related to java, jdbc, spring, etc.

Best RxJava links: map, flatMap, concatMap, and more

As often happens, I have about 50 browser tabs open, and in an effort to close some of those down, these are some of the best links I found while working with RxJava a week or two ago:

RxJava’s Side Effect Methods

RxJava's Observable class has plenty of methods that can be used to transform the stream of emitted items to the kind of data that you need. Those methods are at the very core of RxJava and form a big part of it's attraction. But there are other methods, that do not change the stream of items in any way - I call those methods side effect methods.

How to debug RxJava Observable method calls/chains

As a brief note to self, when you need to debug a chain of RxJava Observable method calls, you can use the doOnNext method to log the current values or print them to STDOUT or STDERR with println. Here’s an example from RxJava For Android Developers, where the debug output is logged with the Android Log.d method:

Jeyes, a Java version of Xeyes

Jeyes, a Java version of Xeyes

In my spare time back in 2011 I created a Java version of the old Unix/X-Windows “Xeyes” application. If you ever used Xeyes, you know it as a set of eyes that are displayed on-screen, and follow the mouse cursor as you move it around.

Now in 2019 I just brought it back to life, and here’s a 56-second video that shows how it works:

A simple RxJava 2 “Hello, world” example

As a brief note, and assuming that you already know a little bit about RxJava, here’s the simplest possible RxJava 2 “Hello, world” example I think you can create:

package hello;

import io.reactivex.Observable;

public class HelloWorld {

    public static void main(String[] args) {
        Observable<String> observable = Observable.just("Hello, world");