[英]Callable lambda expression with argument
我正在嘗試使用泛型(我第一次嘗試使用泛型)和使用ExecutorService來實現“TaskExecutor”。
這是我的“TaskExecutor”類:
public class ExecuteAlerterTask<T> {
public List<T> process(String executorName, Callable<T> task) throws ExecutionException, InterruptedException {
final ThreadFactory threadFactory = new ThreadFactoryBuilder()
.setNameFormat(executorName + "-%d")
.setDaemon(true)
.build();
ExecutorService executor = Executors.newFixedThreadPool(10, threadFactory);
Collection<Future<T>> futures = new ArrayList<>();
IntStream.range(1, 10).forEach(i -> {
Future<T> future = executor.submit(task);
futures.add(future);
});
List<T> result = new ArrayList<>();
for (Future<T> f : futures) {
result.add(f.get());
}
executor.shutdown();
return result;
}
}
這是我運行它的方法:
@Test
public void process() throws Exception {
Callable<String> callable = () -> "Do something on ";
ExecuteAlerterTask<String> executeAlerterTask = new ExecuteAlerterTask<>();
List<String> result = executeAlerterTask.process("TaskName", callable);
result.forEach(System.out::println);
}
這是我的問題 :如何編寫我的Callable,它會在一行接受參數i :
Future<T> future = executor.submit(task);
例如,期望的結果將是:
Do something on 1
Do something on 3
Do something on 7
Do something on 2
<...etc...>
如果我的代碼有其他問題 - 請告訴我。
編輯
刪除了實現Callable
上面的代碼是我真正想要做的事情的抽象 :
EDIT2
在我提出以下解決方案的所有建議后
public class ExecuteAlerterTask<T> {
public List<T> process(String executorName, Collection<Callable<T>> task) throws ExecutionException, InterruptedException {
final ThreadFactory threadFactory = new ThreadFactoryBuilder()
.setNameFormat(executorName + "-%d")
.setDaemon(true)
.build();
ExecutorService executor = Executors.newFixedThreadPool(10, threadFactory);
Collection<Future<T>> futures = executor.invokeAll(task);
List<T> result = new ArrayList<>();
for (Future<T> f : futures) {
result.add(f.get());
}
executor.shutdown();
return result;
}
}
以及運行方式:
@Test
public void process() throws Exception {
Collection<Callable<String>> tasks = new ArrayList<>();
IntStream.range(1, 10).forEach(i -> {
tasks.add(new Task(i).callable);
});
ExecuteAlerterTask<String> executeAlerterTask = new ExecuteAlerterTask<>();
List<String> result = executeAlerterTask.process("TaskName", tasks);
result.forEach(System.out::println);
}
private class Task {
private int i;
private Callable<String> callable = () -> "Doing something on i: " + i;
private Task(int i) {
this.i = i;
}
}
EDIT3
更簡單的運行方式:
@Test
public void process() throws Exception {
Collection<Callable<String>> tasks = new ArrayList<>();
IntStream.range(1, 10).forEach(i -> {
tasks.add(() -> "Do something on i: " + i * 2);
});
ExecuteAlerterTask<String> executeAlerterTask = new ExecuteAlerterTask<>();
List<String> result = executeAlerterTask.process("TaskName", tasks);
result.forEach(System.out::println);
}
我想我對最終解決方案非常滿意。 謝謝大家!
首先,你根本不需要call()
,你也不需要在這個類中實現Callable<T>
,因為你從不使用它。
要以你想要的方式創建一個可調用的,你可以做到
Callable<String> task; // from the parameter
int i; // from the loop
Callable<String> wrapper = () -> { return task.call() + " on " + i; }
executor.submit(wrapper);
你實際上是給lambda外部變量i
作為參數。
這有點不可能。 如果是lambda,則無法將變量傳遞給callable。 另一方面,您可以使用自己的特定對象來實現Callable
,並為變量設置一個setter:
public class CallableWithParam implements Callable<String> {
// protected for subclassing call()
// volatile for multi-threaded reasons
protected volatile int param = 0;
public void setParam(int param) {
this.param = param;
}
@Override
public String call() {
return "my param is: " + param;
}
}
用法:
@Test
public void process() throws Exception {
CallableWithParam callable = new CallableWithParam() {
@Override
public String call() {
// an anonymous inner class is almost a lambda ;)
return "my param is: " + param + "in subclass";
}
};
callable.setParam(3);
ExecuteAlerterTask<String> executeAlerterTask = new ExecuteAlerterTask<>();
List<String> result = executeAlerterTask.process("TaskName", callable);
result.forEach(System.out::println);
}
或者,您可以在構造函數中設置param而不是setter。
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