{"id":55083,"date":"2016-04-19T16:00:00","date_gmt":"2016-04-19T13:00:00","guid":{"rendered":"https:\/\/www.javacodegeeks.com\/?p=55083"},"modified":"2016-04-18T14:05:42","modified_gmt":"2016-04-18T11:05:42","slug":"spring-async-javas-8-completablefuture","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2016\/04\/spring-async-javas-8-completablefuture.html","title":{"rendered":"Spring Async and Java’s 8 CompletableFuture"},"content":{"rendered":"

It is known that I am not the biggest fan of\u00a0Spring<\/a>, but at the time being I work for an organization that maintains too many projects utilizing Spring (in different forms and versions). I still remain skeptic towards Spring, of course there are some very nice ideas, there are some nice (too many) abstractions, there are some very handy ‘shortcuts’ to bootstrap complex projects. I am not going to elaborate on the things I don’t like in this post.<\/span><\/p>\n

One thing I like on Spring’s documentation, is their getting started guides. Well written and concrete. I was reading through, a short guide, for ‘\u00a0Async<\/a>‘ method execution, through\u00a0SpringBoot<\/a> \/RestApi [\u00a0link<\/a>] .<\/p>\n

So this is this the implementation of the example ‘asynchronous’\u00a0findUser() method. Full source\u00a0here<\/a>.<\/p>\n

@Async\r\npublic Future<User> findUser(String user) throws InterruptedException {\r\n  System.out.println(\"Looking up \" + user);\r\n  User results = restTemplate.getForObject(\"https:\/\/api.github.com\/users\/\" + user, User.class);\r\n  \/\/ Artificial delay of 1s for demonstration purposes\r\n  Thread.sleep(1000L);\r\n  return new AsyncResult<User>(results);\r\n}<\/pre>\n
I was wondering why there is still a ‘\u00a0Future’ in the example, while we have been introduced Java8,\u00a0CompletableFuture<\/a>.\u00a0I guess the original authors want to preserve backwards compatibility with previous versions of Java (6 \/ 7 ) – where this construct is not available<\/i>.<\/p>\n
It seems that someone else had the same question, and wrote a very nice example\u00a0here<\/a>. In one of the comments, you can see a hint that from\u00a0version 4.2 <\/a>and onward the Spring API, would be compatible with the use of\u00a0CompletableFuture, on top of\u00a0Future &\u00a0AsyncResult which are already provided. I thought, `\u00a0well it’s a shame, why not try it or even document it, because if someone lands on this example, he\/she might stay with the current implementation<\/i>` – why not use something standard?.
 
<\/div> <\/div><\/p>\n
So I decided to make a tiny change, remove\u00a0Future and replace it with\u00a0CompletableFuture, also comment out the calls to\u00a0Future.isDone()<\/a> and replace it with the very handy\u00a0CompletableFuture.allof()<\/a> method.<\/p>\n
So I changed the return type on the ‘service’ method\u00a0while, updating the, caller code – to sync on all 3 futures and once allof() them were done, we could print the results.<\/p>\n
package hello;\r\n\r\nimport java.util.concurrent.CompletableFuture;\r\nimport java.util.concurrent.Future;\r\n\r\nimport org.springframework.scheduling.annotation.Async;\r\nimport org.springframework.scheduling.annotation.AsyncResult;\r\nimport org.springframework.stereotype.Service;\r\nimport org.springframework.web.client.RestTemplate;\r\n\r\n@Service\r\npublic class GitHubLookupService {\r\n\r\n    RestTemplate restTemplate = new RestTemplate();\r\n\r\n    @Async\r\n    public CompletableFuture findUser(String user) throws InterruptedException {\r\n        System.out.println(\"Looking up \" + user);\r\n        User results = restTemplate.getForObject(\"https:\/\/api.github.com\/users\/\" + user, User.class);\r\n        \/\/ Artificial delay of 1s for demonstration purposes\r\n        Thread.sleep(1000L);\r\n        return CompletableFuture.completedFuture(results);\r\n    }\r\n\r\n}\r\n<\/pre>\n
The modified, example can be found\u00a0here<\/a><\/b>. I found\u00a0this<\/a> and\u00a0this<\/a> blog posts from\u00a0Tomasz Nirkewicz<\/a>, a very nice and pragmatic walk through of\u00a0CompletableFuture, rich method list. There is also a quite complete presentation by my favorite\u00a0Devoxx<\/a> Speaker ,\u00a0Jose Paumard<\/a> you can find it\u00a0here<\/a>.<\/p>\n
@Override\r\n    public void run(String... args) throws Exception {\r\n        \/\/ Start the clock\r\n        long start = System.currentTimeMillis();\r\n\r\n        \/\/ Kick of multiple, asynchronous lookups\r\n        CompletableFuture page1 = gitHubLookupService.findUser(\"PivotalSoftware\");\r\n        CompletableFuture page2 = gitHubLookupService.findUser(\"CloudFoundry\");\r\n        CompletableFuture page3 = gitHubLookupService.findUser(\"Spring-Projects\");\r\n\r\n        \/\/ Wait until they are all done\r\n        \/\/while (!(page1.isDone() && page2.isDone() && page3.isDone())) {\r\n          \/\/  Thread.sleep(10); \/\/10-millisecond pause between each check\r\n        \/\/}\r\n\r\n        \/\/wait until all they are completed.\r\n        CompletableFuture.allOf(page1,page2,page3).join();\r\n        \/\/I could join as well if interested.\r\n\r\n        \/\/ Print results, including elapsed time\r\n        System.out.println(\"Elapsed time: \" + (System.currentTimeMillis() - start) +\" ms\");\r\n        System.out.println(page1.get());\r\n        System.out.println(page2.get());\r\n        System.out.println(page3.get());\r\n    }\r\n<\/pre>\n
Links<\/p>\n