線程中創建子線程，實現保證先執行子線程。

package test;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;


public class ChildThreadTest{
    
    public static void main(String[] args){
        ExecutorService executorService = Executors.newCachedThreadPool();
        Future<Boolean> future = executorService.submit(new Callable<Boolean>() {

            // 子線程1
            @Override
            public Boolean call() throws Exception {
                // 子線程1
                Future<Boolean> future1 = executorService.submit(new Callable<Boolean>() {
                    @Override
                    public Boolean call() throws Exception {
                        Thread.sleep(1000);
                        System.out.println("子線程1執行了...");
                        return true;
                    }
                });
                // 子線程2
                Future<Boolean> future2 = executorService.submit(new Callable<Boolean>() {
                    @Override
                    public Boolean call() throws Exception {
                        System.out.println("子線程2執行了...");
                        return true;
                    }
                });
                // 子線程3
                Future<Boolean> future3 = executorService.submit(new Callable<Boolean>() {
                    @Override
                    public Boolean call() throws Exception {
                        System.out.println("子線程3執行了...");
                        return true;
                    }
                });
                future1.get();
                future2.get();
                future3.get();
                return true;
            }
        });
        try {
            // 阻塞
            future.get();
            System.out.println("外部線程執行了....");
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ExecutionException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            // 啓動有序關閉，在此過程中執行先前提交的任務，但不接受任何新任務。如果已經關閉，調用不會產生額外的效果。
            System.out.println("線程關閉！");
            executorService.shutdown();
        }
    }

}

執行結果：