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POHow does Java Future multithreading return result ?
 

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  1. POHow does Java Future multithreading return result ?
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    <p>I am still learning about using Future and Callable in Java. Stumble into this question:</p> <p>Say I have class:</p> <pre><code>TaskWorker implements Callable { public String id; public TaskWorker(String id) { this.id = id; } public Documents call() trows Exception { //Assume here, that Search and Doc are my own method to search and retrieve docs Search search = new Search(); Documents docResult = search.process(id); //think about documents has getDocs //docResult.getDocs() will return number of document found from search return docResult; } } </code></pre> <p>And here is the main method:</p> <pre><code>public static void main(String[] args) { //assume here, that I build in request contains many Id Request request = new Request(); request.process; ExecutorService service = Executors.newFixedThreadPool(3); List&lt;Future&lt;Documents&gt;&gt; result = new ArrayList&lt;Future&lt;Documents&gt;&gt;(); for (int i=0;i&lt;request.length;i++) { Callable&lt;Documents&gt; worker = new TaskWorker(request.getId[i]); Future&lt;Documents&gt; submit = executor.submit(worker); result.add(submit); } Response response = new Response(); ArrayList&lt;Documents&gt; docList = new ArrayList&lt;Documents&gt;(); for (Future&lt;Documents&gt; future:result) { docList.add(future.get().getDocs()); } response.setDocuments(docList); } </code></pre> <p>What I am trying to do is, breaking a part the request to run in separate thread since each of the request Id is separate Search process. So I am trying to utilize Java pooling, by storing the result in the future object.</p> <p>The thing I am confused is, how does future will work in this case? For each thread completion, is it going to hold the results? And after all the process finish, I can just loop future object to get the results right?</p> <p>Also, there is no guarantee that process will run in order (1,2,3,4,etc), right? If that the case, then what is the best strategy if I want to associate each original request with the future result?</p> <p>Please advise.</p> <p>Thanks</p>
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