java - Java 中的内部 FutureTask

Question

我尝试实现一个内部方法，以便在新线程中执行以下代码

MyPojo result = null;
final MyPojo result2 = result;

FutureTask<MyPojo> runnableTask = new FutureTask<MyPojo>(
    new Runnable() {  

        BindJSON<MyPojo> binding;

        // Make the URL at which the product list is found
        String sourceURLString = 
            "http://www.....ca/files/{CAT_ID}.json";                

        @Override
        public void run() {  
            sourceURLString = sourceURLString.replace("{CAT_ID}", catId);
            binding = new BindJSON<MyPojo>();  
            result2 = binding.downloadData(sourceURLString, MyPojo.class);  
        }  
    }, 
    result2);

runnableTask.run();

所以，现在我收到一个错误:无法分配最终局部变量 result2，因为它是在封闭类型中定义的。我看一下这个答案:Cannot refer to a non-final variable i inside an inner class defined in a different method但这对我不起作用。我应该做什么才能使这项工作成功？

Answer 1

您可能想使用 Callable ，不是 Runnable:

// the variable holding the result of a computation
String result = null;

FutureTask<String> runnableTask = new FutureTask<String>(
        new Callable<String>() {
            public String call() throws Exception {
                // (asynchronous) computation ...
                return "42";
            }
        });

System.out.println("result=" + result); // result=null

// this will invoke call, but it will all happen in the *same thread*
runnableTask.run();

// to have a parallel thread execute in the 'background'
// you can use java.util.concurrent.Executors
// Note: an ExecutorService should be .shutdown() properly
// Executors.newSingleThreadExecutor().submit(runnableTask);

// waits for the result to be available
result = runnableTask.get();

// you can also add timeouts:
// result = runnableTask.get(100, TimeUnit.MILLISECONDS);

System.out.println("result=" + result); // result=42

• 执行者:http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/Executors.html