CODEWITHSUNDEEP
concurrencyparallel-processingjava-8
sunil
sunil

Reputation: 41

How to execute multiple sql query parallel in java

I have 3 method which is returning a List of result and my sql query execute in each method and returning a list of result .I want to execute all 3 method parallel so it will not wait to complete of one and another . I saw one stachoverflow post but its not working. that link is [How to execute multiple queries in parallel instead of sequentially? [Execute multiple queries in parallel via Streams

I want to solve using java 8 features. But the above link how I can call multiple method please tell me.

Upvotes: 0

Views: 6962

Answers (2)

immiKhan
immiKhan

Reputation: 1

The solution from Alex won't work in an expected way. CompletableFuture executes effects one after another. You will have to run parallel streams for this or use CompletableFuture with parallelStream

Upvotes: -1

Alex M981
Alex M981

Reputation: 2374

Execute multiple queries in parallel via Streams works for your task. Here is a sample code which demonstrates it:

public static void main(String[] args) {
    // Create Stream of tasks:
    Stream<Supplier<List<String>>> tasks = Stream.of(
            () -> getServerListFromDB(),
            () -> getAppListFromDB(),
            () -> getUserFromDB());

    List<List<String>> lists = tasks
            // Supply all the tasks for execution and collect CompletableFutures
            .map(CompletableFuture::supplyAsync).collect(Collectors.toList())
            // Join all the CompletableFutures to gather the results
            .stream()
            .map(CompletableFuture::join).collect(Collectors.toList());
    System.out.println(lists);
}

private static List<String> getUserFromDB() {
    try {
        TimeUnit.SECONDS.sleep((long) (Math.random() * 3));
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName() + " getUser");
    return Arrays.asList("User1", "User2", "User3");
}

private static List<String> getAppListFromDB() {
    try {
        TimeUnit.SECONDS.sleep((long) (Math.random() * 3));
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

    System.out.println(Thread.currentThread().getName() + " getAppList");
    return Arrays.asList("App1", "App2", "App3");
}

private static List<String> getServerListFromDB() {
    try {
        TimeUnit.SECONDS.sleep((long) (Math.random() * 3));
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

    System.out.println(Thread.currentThread().getName() + " getServer");
    return Arrays.asList("Server1", "Server2", "Server3");
}

The output is: 

ForkJoinPool.commonPool-worker-1 getServer
ForkJoinPool.commonPool-worker-3 getUser
ForkJoinPool.commonPool-worker-2 getAppList
[[Server1, Server2, Server3], [App1, App2, App3], [User1, User2, User3]]

You can see that default ForkJoinPool.commonPool is used and each get* method is executed from separate thread in this pool. You just need to run your SQL queries inside these get* methods

Upvotes: 1

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