Slides part of Deep dive reactive java live coding session on DevoxxPL.

1. T O M A S Z K O W A L C Z E W S K I

2. Agenda
• A little bit of history
• Challenges before us
• A few words about API
• Code!

3. Reactive, asynchronous
• People have been doing it for years
• (Re)invented time and again by big companies
and/or in high performance products
–Donald Knuth
“The idea that people knew a thing or two in the
70s is strange to a lot of young programmers”

4. Reactive, asynchronous
• People have been doing it for years
• (Re)invented time and again by big companies
and/or in high performance products
• Now every company may need to operate at that
scale
• As users demand more and faster we need tools to
do it right

5. It started in Microsoft

6. Brought to you by Erik Meijer & co.

7. Synchronous pull communication
Client Server
Request
Response
Processing
Network latency

8. Asynchronous push
Processing
Network latency

9. Asynchronous push
t
subscribe
onNext*
onCompleted | onError
unsubscribe

10. Synchronous design
List<String> tweets = client.getNextTweets();
List<Tweet> validTweets = Lists.newArrayList();
for (String jsonTweet : tweets) {
Tweet tweet = gson.fromJson(jsonTweet, Tweet.class);
Image image;
image = download(tweet.getUser().getProfileImage());
Tweet.setImage(image);
if (tweet.isValidTweet()) {
validTweets.add(tweet);
}
}

11. Decomposing individual operations
List<String> tweets = client.getNextTweets();
List<Tweet> validTweets = Lists.newArrayList();
for (String jsonTweet : tweets) {
Tweet tweet = gson.fromJson(jsonTweet, Tweet.class);
Image image;
image = download(tweet.getUser().getProfileImage());
Tweet.setImage(image);
if (tweet.isValidTweet()) {
validTweets.add(tweet);
}
}

12. Decomposing individual operations
List<String> tweets = client.getNextTweets();
List<Tweet> validTweets = Lists.newArrayList();
for (String jsonTweet : tweets) {
Tweet tweet = gson.fromJson(jsonTweet, Tweet.class);
Image image;
image = download(tweet.getUser().getProfileImage());
Tweet.setImage(image);
if (tweet.isValidTweet()) {
validTweets.add(tweet);
}
}

13. Decomposing individual operations
List<String> tweets = client.getNextTweets();
List<Tweet> validTweets = Lists.newArrayList();
for (String jsonTweet : tweets) {
Tweet tweet = gson.fromJson(jsonTweet, Tweet.class);
Image image;
image = download(tweet.getUser().getProfileImage());
Tweet.setImage(image);
if (tweet.isValidTweet()) {
validTweets.add(tweet);
}
}

14. Decomposing individual operations
List<String> tweets = client.getNextTweets();
List<Tweet> validTweets = Lists.newArrayList();
for (String jsonTweet : tweets) {
Tweet tweet = gson.fromJson(jsonTweet, Tweet.class);
Image image;
image = download(tweet.getUser().getProfileImage());
Tweet.setImage(image);
if (tweet.isValidTweet()) {
validTweets.add(tweet);
}
}

15. What is missing?
List<String> tweets = client.getNextTweets();
List<Tweet> validTweets = Lists.newArrayList();
for (String jsonTweet : tweets) {
Tweet tweet = gson.fromJson(jsonTweet, Tweet.class);
Image image;
image = download(tweet.getUser().getProfileImage());
Tweet.setImage(image);
if (tweet.isValidTweet()) {
validTweets.add(tweet);
}
}
Error
handling
Timeouts
Monitoring
Logging
Back pressure
Parallelism

17. Available in a language or
framework near you

18. source: flatmapthatshit.com

19. Credits
• Cat picture taken from http://www.teckler.com/en/
Rapunzel