如何在java中并行运行多个方法并从每个方法中获得输出

Question

我想并行运行三种不同的方法来提高Java的性能。此外，我还需要从他们三个人那里得到输出。下面是我试过的样品。在这里，我不知道如何检索返回的字符串值。请帮我添加(将所有三个字符串连接到总数(。

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class test {
public static void main(String[] args) {
String total = "";
Callable<String> callable1 = new Callable<String>()
{
@Override
public String call() throws Exception
{
String t1 = "";
t1 = method1();
return t1;
}
};
Callable<String> callable2 = new Callable<String>()
{
@Override
public String call() throws Exception
{
String t2 = method2();
return t2;
}
};
Callable<String> callable3 = new Callable<String>()
{
@Override
public String call() throws Exception
{
String t3 = method3();
return t3;
}
};
List<Callable<String>> taskList = new ArrayList<Callable<String>>();
taskList.add(callable1);
taskList.add(callable2);
taskList.add(callable3);
ExecutorService executor = Executors.newFixedThreadPool(3);
try
{
executor.invokeAll(taskList);
//total = ;(want to concatenate all the strings here).
System.out.println(total);
}
catch (InterruptedException ie)
{
//do something if you care about interruption;
}
}
public static String method1()
{
System.out.println("method1");
return "1";
}
private static String method2()
{
System.out.println("method2");
return "2";
}
private static String method3()
{
System.out.println("method3");
return "3";
}

}

Answer 1

由于taskList是List<Callable<String>>，executor.invokeAll(taskList)返回一个List<Future<String>>，其中包含对应于taskList中每个任务的Future<String>。您需要保存List<Future<String>>，以便以后可以查看任务的结果。类似这样的东西：

List<Future<String>> futureList = executor.invokeAll(tasklist);
String result = futureList.get(0).get() +
futureList.get(1).get() +
futureList.get(2).get();

除了InterruptedException，Future.get()还可以抛出CancellationException和ExecutionException，因此您需要准备好在try块中处理这些问题。

Answer 2

由于任务数量很少，您可以创建3个CompletableFutures并在其上进行流式传输并加入它。

CompletableFuture<String> task1 = CompletableFuture.supplyAsync(() -> method1());
CompletableFuture<String> task2 = CompletableFuture.supplyAsync(() -> method2());
CompletableFuture<String> task3 = CompletableFuture.supplyAsync(() -> method3());
String concate = Stream.of(task1, task2, task3)
.map(CompletableFuture::join)
.reduce("", (s1, s2) -> s1 + s2);
System.out.println(concate);

Answer 3

在@Govinda答案上添加-您可以使用supplyAsync工厂方法创建CompletableFuture的Stream，通过调用CompletableFuture::join来完成，并通过调用Collectors.joining()来完成concat。

CompletableFuture<String> task1 = CompletableFuture.supplyAsync(Test::method1);      
CompletableFuture<String> task2 = CompletableFuture.supplyAsync(Test::method2);      
CompletableFuture<String> task3 = CompletableFuture.supplyAsync(Test::method3);      
                        
String concat =                                                                               
Stream.of(task1, task2, task3).map(CompletableFuture::join).collect(Collectors.joining());
System.out.println(concat);