Future将从执行程序服务提交返回null

Question

在执行Java到Groovy代码迁移的初始阶段时,我遇到了一个问题,即Groovy版本从Future返回null,而Java返回正确的整数(123).

J1.java和G1.groovy之间唯一的变化是类名和lambda到闭包转换.

//文件:J1.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class J1 {
  public static void main (String... args) throws Exception {
    ExecutorService executor = Executors.newFixedThreadPool (1);
    Future<Integer> future = executor.submit (() -> 123);
    System.out.println ("Result: " + future.get ());
    executor.shutdown ();
  }
}

//文件:G1.groovy

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class G1 {
  public static void main (String... args) throws Exception {
    ExecutorService executor = Executors.newFixedThreadPool (1);
    Future<Integer> future = executor.submit ({ -> 123 });
    System.out.println ("Result: " + future.get ());
    executor.shutdown ();
  }
}

Java结果:123

Groovy结果:null

这是预期的,如果是这样,为什么？我尝试了很多变化,都产生了相同的结果.是否有一些我缺少使用Groovy产生相同结果的东西？

Groovy: 2.4.5
Java: 1.8 64-bit
Platform: Windows 7 64-bit

Answer 1

在Groovy中,闭包是a Runnable和a Callable.

不幸的是,当你调用时executor.submit { .. },运行时选择调用executor.submit(Runnable)哪个不返回值.

你应该明确地将你的闭包转换为Callable:

def executor = Executors.newFixedThreadPool(1)
def future = executor.submit ({ -> 123 } as Callable)
println "Result: ${future.get()}"
executor.shutdown()