本文详细对比了线程池中的submit与execute方法，包括它们的参数差异、异常处理方式及应用场景。submit能提交Runnable和Callable任务并返回Future，execute仅支持Runnable任务且异常直接抛出。
execute和submit都属于线程池的方法，execute只能提交Runnable类型的任务，而submit既能提交Runnable类型任务也能提交Callable类型任务。
execute会直接抛出任务执行时的异常，submit会吃掉异常，可通过Future的get方法将任务执行时的异常重新抛出。
execute所属顶层接口是Executor,submit所属顶层接口是ExecutorService，实现类ThreadPoolExecutor重写了execute方法,抽象类AbstractExecutorService重写了submit方法。
submit和execute由于参数不同有四种实现形式，如下所示，本文主要研究这四种形式在各自使用场景下的区别和联系
<T> Future<T> submit(Callable<T> task);
<T> Future<T> submit(Runnable task, T result);
Future<?> submit(Runnable task);
void execute(Runnable command);关于Runnable和Callable任务如果你还存在疑惑，建议你先看看我的上篇文章Runnable和Callable的区别和联系。
测试代码的整体框架如下：
import java.util.concurrent.*;
public class TestSubmitAndExecute {
static ExecutorService executor = Executors.newCachedThreadPool();
public static void main(String[] args) {
initExecutors();
/**put test codes here*/
/***/
waitToTerminated();
}
private static void initExecutors() {
if (executor.isTerminated()) {
executor = Executors.newCachedThreadPool();
}
}
private static void waitToTerminated() {
executor.shutdown();
while (!executor.isTerminated()) {
}
}
/**
* 测试 submit(Callable<T> task)
*
* @param callable
* @param <T>
* @return
*/
public static <T> T testSubmitCallable(Callable callable) {
Future<T> future = executor.submit(callable);
T result = null;
try {
result = future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
return result;
}
/**
* 测试submit(Runnable task, T result)
*
* @param runnable
* @param t
* @param <T>
* @return
*/
public static <T> T testSubmitRunnable(Runnable runnable, T t) {
Future<T> future = executor.submit(runnable, t);
T result = null;
try {
result = future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
return result;
}
/**
* 测试 submit(Runnable task)
* submit提交Runnable任务会默认返回null
*
* @param runnable
* @return
*/
public static Object testSubmitRunnable(Runnable runnable) {
Future<?> future = executor.submit(runnable);
Object v = null;
try {
v = future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
return v;
}
/**
* 测试 execute(Runnable command)
* execute会直接抛出异常，submit只有通过调用Future对象的get方法才能获取异常
*
* @param runnable
*/
public static void testExecuteRunnable(Runnable runnable) {
executor.execute(runnable);
}
}
这个测试框架提供了4个静态方法用来测试submit和execute总共包含的四种表现形式，除此之外提供initExecutors用于提前检测线程池是否终止，若终止则初始化，waitToTerminated方法用于关闭线程池，并阻塞到线程池终止为止。
除了测试框架之外提供了4个不同的任务，分别测试Callable和Runnable在抛异常时的表现形式。
class CallableTask implements Callable<Integer> {
@Override
public Integer call() throws Exception {
int sum = 0;
for (int i = 0; i < 520; i++) {
sum += i;
}
return sum;
}
}
/**
* 会抛异常的CallableTask
*/
class ExceptionCallableTask implements Callable<Boolean> {
public Boolean call() throws Exception {
int num = 1 / 0;
return false;
}
}
class RunnableTask implements Runnable {
@Override
public void run() {
System.out.println("I am a runnable task");
}
}
/**
* 会抛异常的RunnableTask
*/
class ExceptionRunableTask implements Runnable {
@Override
public void run() {
int num = 1 / 0;
}
}整体结构搭起来，下来就是研究具体差异的时刻了。
1）首先研究Future<?> submit(Runnable task)和void execute(Runnable command)，这两个方法都是执行Runnable类型任务，前者有返回值，但是返回值为null，后者无返回值。
public static void main(String[] args) {
initExecutors();
/**put test codes here*/
Object object = testSubmitRunnable(new RunnableTask());
System.out.println(object);
testExecuteRunnable(new RunnableTask());
/***/
waitToTerminated();
}很容易观察控制台输出如下：
I am a runnable task
null
I am a runnable task可以看出submit执行Runnable类型任务时默认返回值为null。如果我们需要submit在提交Runnable任务可以返回非空，就需要用到submit的另外一个重载的方法：<T> Future<T> submit(Runnable task, T result);
2）submit(Runnable task, T result) 方法可以使submit执行完Runnable任务后返回指定的返回值。
main方法如下：
public static void main(String[] args) {
initExecutors();
/**put test codes here*/
// Object object = testSubmitRunnable(new RunnableTask());
// System.out.println(object);
//
// testExecuteRunnable(new RunnableTask());
Integer i = testSubmitRunnable(new RunnableTask(), 3);
System.out.println(i);
Boolean bool = testSubmitRunnable(new RunnableTask(), true);
System.out.println(bool);
String str = testSubmitRunnable(new RunnableTask(), "你好吗");
System.out.println(str);
/***/
waitToTerminated();
}控制台输出：
I am a runnable task
3
I am a runnable task
true
I am a runnable task
你好吗可以看出我们输入的什么参数，任务执行完毕后就返回什么参数。
3）submit(Callable<T> task)这个方法没什么好说的，用来提交Callable类型任务，返回值由call方法决定。
main方法如下：
public static void main(String[] args) {
initExecutors();
/**put test codes here*/
// Object object = testSubmitRunnable(new RunnableTask());
// System.out.println(object);
//
// testExecuteRunnable(new RunnableTask());
// Integer i = testSubmitRunnable(new RunnableTask(), 3);
// System.out.println(i);
//
// Boolean bool = testSubmitRunnable(new RunnableTask(), true);
// System.out.println(bool);
//
// String str = testSubmitRunnable(new RunnableTask(), "你好吗");
// System.out.println(str);
Object o = testSubmitCallable(new CallableTask());
System.out.println(o);
/***/
waitToTerminated();
}CallableTask的执行逻辑是计算0到520之间的所有整数之和，所以控制台输出：
1349404）关于execute和submit遭遇异常的表现
execute直接将任务执行时期的异常抛出，main方法和控制台打印分别如下：
public static void main(String[] args) {
initExecutors();
/**put test codes here*/
// Object object = testSubmitRunnable(new RunnableTask());
// System.out.println(object);
//
// testExecuteRunnable(new RunnableTask());
// Integer i = testSubmitRunnable(new RunnableTask(), 3);
// System.out.println(i);
//
// Boolean bool = testSubmitRunnable(new RunnableTask(), true);
// System.out.println(bool);
//
// String str = testSubmitRunnable(new RunnableTask(), "你好吗");
// System.out.println(str);
// Object o = testSubmitCallable(new CallableTask());
// System.out.println(o);
testExecuteRunnable(new ExceptionRunableTask());
/***/
waitToTerminated();
}
Exception in thread "pool-1-thread-1" java.lang.ArithmeticException: / by zero
at ExceptionRunableTask.run(TestRunnableAndCallable.java:38)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
submit比较特殊，如果没有通过Future.get来获取结算结果，则吃掉异常。先将测试方法稍做调整，修改成如下形式：
/**
* 测试 submit(Callable<T> task)
*
* @param callable
* @param <T>
* @return
*/
public static <T> T testSubmitCallable(Callable callable) {
Future<T> future = executor.submit(callable);
T result = null;
/*
try {
result = future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
*/
return result;
}当我们在main方法添加如下代码时，控制台其实没有打印任何异常
public static void main(String[] args) {
initExecutors();
/**put test codes here*/
// Object object = testSubmitRunnable(new RunnableTask());
// System.out.println(object);
//
// testExecuteRunnable(new RunnableTask());
// Integer i = testSubmitRunnable(new RunnableTask(), 3);
// System.out.println(i);
//
// Boolean bool = testSubmitRunnable(new RunnableTask(), true);
// System.out.println(bool);
//
// String str = testSubmitRunnable(new RunnableTask(), "你好吗");
// System.out.println(str);
// Object o = testSubmitCallable(new CallableTask());
// System.out.println(o);
// testExecuteRunnable(new ExceptionRunableTask());
testSubmitCallable(new ExceptionCallableTask());
/***/
waitToTerminated();
}如果将testSubmitCallable代码中被注释的部分取消注释，则可以看到异常信息如下：
java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at TestSubmitAndExecute.testSubmitCallable(TestSubmitAndExecute.java:58)
at TestSubmitAndExecute.main(TestSubmitAndExecute.java:28)
Caused by: java.lang.ArithmeticException: / by zero
at ExceptionCallableTask.call(TestRunnableAndCallable.java:20)
at ExceptionCallableTask.call(TestRunnableAndCallable.java:18)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
关于execute和submit的简单研究到此结束，谢谢观看。
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