Java线程池技术

╰+攻爆jí腚メ 2022-07-13 06:47 175阅读 0赞

**线程池的优点**

1、线程是稀缺资源，使用线程池可以减少创建和销毁线程的次数，每个工作线程都可以重复使用。

2、可以根据系统的承受能力，调整线程池中工作线程的数量，防止因为消耗过多内存导致服务器崩溃。

**线程池的创建**

public static ExecutorService newCachedThreadPool() {
 return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
 60L, TimeUnit.SECONDS,
 new SynchronousQueue<Runnable>());
 }

public ThreadPoolExecutor(int corePoolSize,
 int maximumPoolSize,
 long keepAliveTime,
 TimeUnit unit,
 BlockingQueue<Runnable> workQueue,
 ThreadFactory threadFactory,
 RejectedExecutionHandler handler) {
 if (corePoolSize < 0 ||
 maximumPoolSize <= 0 ||
 maximumPoolSize < corePoolSize ||
 keepAliveTime < 0)
 throw new IllegalArgumentException();
 if (workQueue == null || threadFactory == null || handler == null)
 throw new NullPointerException();
 this.corePoolSize = corePoolSize;
 this.maximumPoolSize = maximumPoolSize;
 this.workQueue = workQueue;
 this.keepAliveTime = unit.toNanos(keepAliveTime);
 this.threadFactory = threadFactory;
 this.handler = handler;
 }

corePoolSize：线程池核心线程数量

maximumPoolSize:线程池最大线程数量

keepAliverTime：当活跃线程数大于核心线程数时，空闲的多余线程最大存活时间

unit：存活时间的单位

workQueue：存放任务的队列

handler：超出线程范围和队列容量的任务的处理程序

**线程池的实现原理**

提交一个任务到线程池中，线程池的处理流程如下：

1、判断线程池里的核心线程是否都在执行任务，如果不是（核心线程空闲或者还有核心线程没有被创建）则创建一个新的工作线程来执行任务。如果核心线程都在执行任务，则进入下个流程。

2、线程池判断工作队列是否已满，如果工作队列没有满，则将新提交的任务存储在这个工作队列里。如果工作队列满了，则进入下个流程。

3、判断线程池里的线程是否都处于工作状态，如果没有，则创建一个新的工作线程来执行任务。如果已经满了，则交给饱和策略来处理这个任务。

**Executors方法**

生成线程池采用了工具类Executors的静态方法，以下是几种常见的线程池。

newCachedThreadPool创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。

newFixedThreadPool 创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待。

newScheduledThreadPool 创建一个定长线程池，支持定时及周期性任务执行。

newSingleThreadExecutor 创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。

/* * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */
 
 /* * * * * * * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 package java.util.concurrent;
 import java.util.*;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.security.AccessControlContext;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.security.PrivilegedExceptionAction;
 import java.security.PrivilegedActionException;
 import java.security.AccessControlException;
 import sun.security.util.SecurityConstants;
 
 /** * Factory and utility methods for {@link Executor}, {@link * ExecutorService}, {@link ScheduledExecutorService}, {@link * ThreadFactory}, and {@link Callable} classes defined in this * package. This class supports the following kinds of methods: * * <ul> * <li> Methods that create and return an {@link ExecutorService} * set up with commonly useful configuration settings. * <li> Methods that create and return a {@link ScheduledExecutorService} * set up with commonly useful configuration settings. * <li> Methods that create and return a "wrapped" ExecutorService, that * disables reconfiguration by making implementation-specific methods * inaccessible. * <li> Methods that create and return a {@link ThreadFactory} * that sets newly created threads to a known state. * <li> Methods that create and return a {@link Callable} * out of other closure-like forms, so they can be used * in execution methods requiring <tt>Callable</tt>. * </ul> * * @since 1.5 * @author Doug Lea */
 public class Executors { 
 
 /** * Creates a thread pool that reuses a fixed number of threads * operating off a shared unbounded queue. At any point, at most * <tt>nThreads</tt> threads will be active processing tasks. * If additional tasks are submitted when all threads are active, * they will wait in the queue until a thread is available. * If any thread terminates due to a failure during execution * prior to shutdown, a new one will take its place if needed to * execute subsequent tasks. The threads in the pool will exist * until it is explicitly {@link ExecutorService#shutdown shutdown}. * * @param nThreads the number of threads in the pool * @return the newly created thread pool * @throws IllegalArgumentException if {@code nThreads <= 0} */
 public static ExecutorService newFixedThreadPool(int nThreads) {
 return new ThreadPoolExecutor(nThreads, nThreads,
 0L, TimeUnit.MILLISECONDS,
 new LinkedBlockingQueue<Runnable>());
 }
 
 /** * Creates a thread pool that reuses a fixed number of threads * operating off a shared unbounded queue, using the provided * ThreadFactory to create new threads when needed. At any point, * at most <tt>nThreads</tt> threads will be active processing * tasks. If additional tasks are submitted when all threads are * active, they will wait in the queue until a thread is * available. If any thread terminates due to a failure during * execution prior to shutdown, a new one will take its place if * needed to execute subsequent tasks. The threads in the pool will * exist until it is explicitly {@link ExecutorService#shutdown * shutdown}. * * @param nThreads the number of threads in the pool * @param threadFactory the factory to use when creating new threads * @return the newly created thread pool * @throws NullPointerException if threadFactory is null * @throws IllegalArgumentException if {@code nThreads <= 0} */
 public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
 return new ThreadPoolExecutor(nThreads, nThreads,
 0L, TimeUnit.MILLISECONDS,
 new LinkedBlockingQueue<Runnable>(),
 threadFactory);
 }
 
 /** * Creates an Executor that uses a single worker thread operating * off an unbounded queue. (Note however that if this single * thread terminates due to a failure during execution prior to * shutdown, a new one will take its place if needed to execute * subsequent tasks.) Tasks are guaranteed to execute * sequentially, and no more than one task will be active at any * given time. Unlike the otherwise equivalent * <tt>newFixedThreadPool(1)</tt> the returned executor is * guaranteed not to be reconfigurable to use additional threads. * * @return the newly created single-threaded Executor */
 public static ExecutorService newSingleThreadExecutor() {
 return new FinalizableDelegatedExecutorService
 (new ThreadPoolExecutor(1, 1,
 0L, TimeUnit.MILLISECONDS,
 new LinkedBlockingQueue<Runnable>()));
 }
 
 /** * Creates an Executor that uses a single worker thread operating * off an unbounded queue, and uses the provided ThreadFactory to * create a new thread when needed. Unlike the otherwise * equivalent <tt>newFixedThreadPool(1, threadFactory)</tt> the * returned executor is guaranteed not to be reconfigurable to use * additional threads. * * @param threadFactory the factory to use when creating new * threads * * @return the newly created single-threaded Executor * @throws NullPointerException if threadFactory is null */
 public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
 return new FinalizableDelegatedExecutorService
 (new ThreadPoolExecutor(1, 1,
 0L, TimeUnit.MILLISECONDS,
 new LinkedBlockingQueue<Runnable>(),
 threadFactory));
 }
 
 /** * Creates a thread pool that creates new threads as needed, but * will reuse previously constructed threads when they are * available. These pools will typically improve the performance * of programs that execute many short-lived asynchronous tasks. * Calls to <tt>execute</tt> will reuse previously constructed * threads if available. If no existing thread is available, a new * thread will be created and added to the pool. Threads that have * not been used for sixty seconds are terminated and removed from * the cache. Thus, a pool that remains idle for long enough will * not consume any resources. Note that pools with similar * properties but different details (for example, timeout parameters) * may be created using {@link ThreadPoolExecutor} constructors. * * @return the newly created thread pool */
 public static ExecutorService newCachedThreadPool() {
 return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
 60L, TimeUnit.SECONDS,
 new SynchronousQueue<Runnable>());
 }
 
 /** * Creates a thread pool that creates new threads as needed, but * will reuse previously constructed threads when they are * available, and uses the provided * ThreadFactory to create new threads when needed. * @param threadFactory the factory to use when creating new threads * @return the newly created thread pool * @throws NullPointerException if threadFactory is null */
 public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
 return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
 60L, TimeUnit.SECONDS,
 new SynchronousQueue<Runnable>(),
 threadFactory);
 }
 
 /** * Creates a single-threaded executor that can schedule commands * to run after a given delay, or to execute periodically. * (Note however that if this single * thread terminates due to a failure during execution prior to * shutdown, a new one will take its place if needed to execute * subsequent tasks.) Tasks are guaranteed to execute * sequentially, and no more than one task will be active at any * given time. Unlike the otherwise equivalent * <tt>newScheduledThreadPool(1)</tt> the returned executor is * guaranteed not to be reconfigurable to use additional threads. * @return the newly created scheduled executor */
 public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
 return new DelegatedScheduledExecutorService
 (new ScheduledThreadPoolExecutor(1));
 }
 
 /** * Creates a single-threaded executor that can schedule commands * to run after a given delay, or to execute periodically. (Note * however that if this single thread terminates due to a failure * during execution prior to shutdown, a new one will take its * place if needed to execute subsequent tasks.) Tasks are * guaranteed to execute sequentially, and no more than one task * will be active at any given time. Unlike the otherwise * equivalent <tt>newScheduledThreadPool(1, threadFactory)</tt> * the returned executor is guaranteed not to be reconfigurable to * use additional threads. * @param threadFactory the factory to use when creating new * threads * @return a newly created scheduled executor * @throws NullPointerException if threadFactory is null */
 public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
 return new DelegatedScheduledExecutorService
 (new ScheduledThreadPoolExecutor(1, threadFactory));
 }
 
 /** * Creates a thread pool that can schedule commands to run after a * given delay, or to execute periodically. * @param corePoolSize the number of threads to keep in the pool, * even if they are idle. * @return a newly created scheduled thread pool * @throws IllegalArgumentException if {@code corePoolSize < 0} */
 public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
 return new ScheduledThreadPoolExecutor(corePoolSize);
 }
 
 /** * Creates a thread pool that can schedule commands to run after a * given delay, or to execute periodically. * @param corePoolSize the number of threads to keep in the pool, * even if they are idle. * @param threadFactory the factory to use when the executor * creates a new thread. * @return a newly created scheduled thread pool * @throws IllegalArgumentException if {@code corePoolSize < 0} * @throws NullPointerException if threadFactory is null */
 public static ScheduledExecutorService newScheduledThreadPool(
 int corePoolSize, ThreadFactory threadFactory) {
 return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
 }
 
 
 /** * Returns an object that delegates all defined {@link * ExecutorService} methods to the given executor, but not any * other methods that might otherwise be accessible using * casts. This provides a way to safely "freeze" configuration and * disallow tuning of a given concrete implementation. * @param executor the underlying implementation * @return an <tt>ExecutorService</tt> instance * @throws NullPointerException if executor null */
 public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
 if (executor == null)
 throw new NullPointerException();
 return new DelegatedExecutorService(executor);
 }
 
 /** * Returns an object that delegates all defined {@link * ScheduledExecutorService} methods to the given executor, but * not any other methods that might otherwise be accessible using * casts. This provides a way to safely "freeze" configuration and * disallow tuning of a given concrete implementation. * @param executor the underlying implementation * @return a <tt>ScheduledExecutorService</tt> instance * @throws NullPointerException if executor null */
 public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
 if (executor == null)
 throw new NullPointerException();
 return new DelegatedScheduledExecutorService(executor);
 }
 
 /** * Returns a default thread factory used to create new threads. * This factory creates all new threads used by an Executor in the * same {@link ThreadGroup}. If there is a {@link * java.lang.SecurityManager}, it uses the group of {@link * System#getSecurityManager}, else the group of the thread * invoking this <tt>defaultThreadFactory</tt> method. Each new * thread is created as a non-daemon thread with priority set to * the smaller of <tt>Thread.NORM_PRIORITY</tt> and the maximum * priority permitted in the thread group. New threads have names * accessible via {@link Thread#getName} of * pool-N-thread-M, where N is the sequence * number of this factory, and M is the sequence number * of the thread created by this factory. * @return a thread factory */
 public static ThreadFactory defaultThreadFactory() {
 return new DefaultThreadFactory();
 }
 
 /** * Returns a thread factory used to create new threads that * have the same permissions as the current thread. * This factory creates threads with the same settings as {@link * Executors#defaultThreadFactory}, additionally setting the * AccessControlContext and contextClassLoader of new threads to * be the same as the thread invoking this * <tt>privilegedThreadFactory</tt> method. A new * <tt>privilegedThreadFactory</tt> can be created within an * {@link AccessController#doPrivileged} action setting the * current thread's access control context to create threads with * the selected permission settings holding within that action. * * Note that while tasks running within such threads will have * the same access control and class loader settings as the * current thread, they need not have the same {@link * java.lang.ThreadLocal} or {@link * java.lang.InheritableThreadLocal} values. If necessary, * particular values of thread locals can be set or reset before * any task runs in {@link ThreadPoolExecutor} subclasses using * {@link ThreadPoolExecutor#beforeExecute}. Also, if it is * necessary to initialize worker threads to have the same * InheritableThreadLocal settings as some other designated * thread, you can create a custom ThreadFactory in which that * thread waits for and services requests to create others that * will inherit its values. * * @return a thread factory * @throws AccessControlException if the current access control * context does not have permission to both get and set context * class loader. */
 public static ThreadFactory privilegedThreadFactory() {
 return new PrivilegedThreadFactory();
 }
 
 /** * Returns a {@link Callable} object that, when * called, runs the given task and returns the given result. This * can be useful when applying methods requiring a * <tt>Callable</tt> to an otherwise resultless action. * @param task the task to run * @param result the result to return * @return a callable object * @throws NullPointerException if task null */
 public static <T> Callable<T> callable(Runnable task, T result) {
 if (task == null)
 throw new NullPointerException();
 return new RunnableAdapter<T>(task, result);
 }
 
 /** * Returns a {@link Callable} object that, when * called, runs the given task and returns <tt>null</tt>. * @param task the task to run * @return a callable object * @throws NullPointerException if task null */
 public static Callable<Object> callable(Runnable task) {
 if (task == null)
 throw new NullPointerException();
 return new RunnableAdapter<Object>(task, null);
 }
 
 /** * Returns a {@link Callable} object that, when * called, runs the given privileged action and returns its result. * @param action the privileged action to run * @return a callable object * @throws NullPointerException if action null */
 public static Callable<Object> callable(final PrivilegedAction<?> action) {
 if (action == null)
 throw new NullPointerException();
 return new Callable<Object>() {
 public Object call() { return action.run(); }};
 }
 
 /** * Returns a {@link Callable} object that, when * called, runs the given privileged exception action and returns * its result. * @param action the privileged exception action to run * @return a callable object * @throws NullPointerException if action null */
 public static Callable<Object> callable(final PrivilegedExceptionAction<?> action) {
 if (action == null)
 throw new NullPointerException();
 return new Callable<Object>() {
 public Object call() throws Exception { return action.run(); }};
 }
 
 /** * Returns a {@link Callable} object that will, when * called, execute the given <tt>callable</tt> under the current * access control context. This method should normally be * invoked within an {@link AccessController#doPrivileged} action * to create callables that will, if possible, execute under the * selected permission settings holding within that action; or if * not possible, throw an associated {@link * AccessControlException}. * @param callable the underlying task * @return a callable object * @throws NullPointerException if callable null * */
 public static <T> Callable<T> privilegedCallable(Callable<T> callable) {
 if (callable == null)
 throw new NullPointerException();
 return new PrivilegedCallable<T>(callable);
 }
 
 /** * Returns a {@link Callable} object that will, when * called, execute the given <tt>callable</tt> under the current * access control context, with the current context class loader * as the context class loader. This method should normally be * invoked within an {@link AccessController#doPrivileged} action * to create callables that will, if possible, execute under the * selected permission settings holding within that action; or if * not possible, throw an associated {@link * AccessControlException}. * @param callable the underlying task * * @return a callable object * @throws NullPointerException if callable null * @throws AccessControlException if the current access control * context does not have permission to both set and get context * class loader. */
 public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> callable) {
 if (callable == null)
 throw new NullPointerException();
 return new PrivilegedCallableUsingCurrentClassLoader<T>(callable);
 }
 
 // Non-public classes supporting the public methods
 
 /** * A callable that runs given task and returns given result */
 static final class RunnableAdapter<T> implements Callable<T> {
 final Runnable task;
 final T result;
 RunnableAdapter(Runnable task, T result) {
 this.task = task;
 this.result = result;
 }
 public T call() {
 task.run();
 return result;
 }
 }
 
 /** * A callable that runs under established access control settings */
 static final class PrivilegedCallable<T> implements Callable<T> {
 private final Callable<T> task;
 private final AccessControlContext acc;
 
 PrivilegedCallable(Callable<T> task) {
 this.task = task;
 this.acc = AccessController.getContext();
 }
 
 public T call() throws Exception {
 try {
 return AccessController.doPrivileged(
 new PrivilegedExceptionAction<T>() {
 public T run() throws Exception {
 return task.call();
 }
 }, acc);
 } catch (PrivilegedActionException e) {
 throw e.getException();
 }
 }
 }
 
 /** * A callable that runs under established access control settings and * current ClassLoader */
 static final class PrivilegedCallableUsingCurrentClassLoader<T> implements Callable<T> {
 private final Callable<T> task;
 private final AccessControlContext acc;
 private final ClassLoader ccl;
 
 PrivilegedCallableUsingCurrentClassLoader(Callable<T> task) {
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 // Calls to getContextClassLoader from this class
 // never trigger a security check, but we check
 // whether our callers have this permission anyways.
 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
 
 // Whether setContextClassLoader turns out to be necessary
 // or not, we fail fast if permission is not available.
 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
 }
 this.task = task;
 this.acc = AccessController.getContext();
 this.ccl = Thread.currentThread().getContextClassLoader();
 }
 
 public T call() throws Exception {
 try {
 return AccessController.doPrivileged(
 new PrivilegedExceptionAction<T>() {
 public T run() throws Exception {
 Thread t = Thread.currentThread();
 ClassLoader cl = t.getContextClassLoader();
 if (ccl == cl) {
 return task.call();
 } else {
 t.setContextClassLoader(ccl);
 try {
 return task.call();
 } finally {
 t.setContextClassLoader(cl);
 }
 }
 }
 }, acc);
 } catch (PrivilegedActionException e) {
 throw e.getException();
 }
 }
 }
 
 /** * The default thread factory */
 static class DefaultThreadFactory implements ThreadFactory {
 private static final AtomicInteger poolNumber = new AtomicInteger(1);
 private final ThreadGroup group;
 private final AtomicInteger threadNumber = new AtomicInteger(1);
 private final String namePrefix;
 
 DefaultThreadFactory() {
 SecurityManager s = System.getSecurityManager();
 group = (s != null) ? s.getThreadGroup() :
 Thread.currentThread().getThreadGroup();
 namePrefix = "pool-" +
 poolNumber.getAndIncrement() +
 "-thread-";
 }
 
 public Thread newThread(Runnable r) {
 Thread t = new Thread(group, r,
 namePrefix + threadNumber.getAndIncrement(),
 0);
 if (t.isDaemon())
 t.setDaemon(false);
 if (t.getPriority() != Thread.NORM_PRIORITY)
 t.setPriority(Thread.NORM_PRIORITY);
 return t;
 }
 }
 
 /** * Thread factory capturing access control context and class loader */
 static class PrivilegedThreadFactory extends DefaultThreadFactory {
 private final AccessControlContext acc;
 private final ClassLoader ccl;
 
 PrivilegedThreadFactory() {
 super();
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 // Calls to getContextClassLoader from this class
 // never trigger a security check, but we check
 // whether our callers have this permission anyways.
 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
 
 // Fail fast
 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
 }
 this.acc = AccessController.getContext();
 this.ccl = Thread.currentThread().getContextClassLoader();
 }
 
 public Thread newThread(final Runnable r) {
 return super.newThread(new Runnable() {
 public void run() {
 AccessController.doPrivileged(new PrivilegedAction<Void>() {
 public Void run() {
 Thread.currentThread().setContextClassLoader(ccl);
 r.run();
 return null;
 }
 }, acc);
 }
 });
 }
 }
 
 /** * A wrapper class that exposes only the ExecutorService methods * of an ExecutorService implementation. */
 static class DelegatedExecutorService extends AbstractExecutorService {
 private final ExecutorService e;
 DelegatedExecutorService(ExecutorService executor) { e = executor; }
 public void execute(Runnable command) { e.execute(command); }
 public void shutdown() { e.shutdown(); }
 public List<Runnable> shutdownNow() { return e.shutdownNow(); }
 public boolean isShutdown() { return e.isShutdown(); }
 public boolean isTerminated() { return e.isTerminated(); }
 public boolean awaitTermination(long timeout, TimeUnit unit)
 throws InterruptedException {
 return e.awaitTermination(timeout, unit);
 }
 public Future<?> submit(Runnable task) {
 return e.submit(task);
 }
 public <T> Future<T> submit(Callable<T> task) {
 return e.submit(task);
 }
 public <T> Future<T> submit(Runnable task, T result) {
 return e.submit(task, result);
 }
 public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
 throws InterruptedException {
 return e.invokeAll(tasks);
 }
 public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
 long timeout, TimeUnit unit)
 throws InterruptedException {
 return e.invokeAll(tasks, timeout, unit);
 }
 public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
 throws InterruptedException, ExecutionException {
 return e.invokeAny(tasks);
 }
 public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
 long timeout, TimeUnit unit)
 throws InterruptedException, ExecutionException, TimeoutException {
 return e.invokeAny(tasks, timeout, unit);
 }
 }
 
 static class FinalizableDelegatedExecutorService
 extends DelegatedExecutorService {
 FinalizableDelegatedExecutorService(ExecutorService executor) {
 super(executor);
 }
 protected void finalize() {
 super.shutdown();
 }
 }
 
 /** * A wrapper class that exposes only the ScheduledExecutorService * methods of a ScheduledExecutorService implementation. */
 static class DelegatedScheduledExecutorService
 extends DelegatedExecutorService
 implements ScheduledExecutorService {
 private final ScheduledExecutorService e;
 DelegatedScheduledExecutorService(ScheduledExecutorService executor) {
 super(executor);
 e = executor;
 }
 public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
 return e.schedule(command, delay, unit);
 }
 public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
 return e.schedule(callable, delay, unit);
 }
 public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
 return e.scheduleAtFixedRate(command, initialDelay, period, unit);
 }
 public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
 return e.scheduleWithFixedDelay(command, initialDelay, delay, unit);
 }
 }
 
 
 /** Cannot instantiate. */
 private Executors() {}
 }

\*execute()方法实际上是Executor中声明的方法，在ThreadPoolExecutor进行了具体的实现，这个方法是ThreadPoolExecutor的核心方法，通过这个方法可以向线程池提交一个任务，交由线程池去执行。  
　　submit()方法是在ExecutorService中声明的方法，在AbstractExecutorService就已经有了具体的实现，在ThreadPoolExecutor中并没有对其进行重写，这个方法也是用来向线程池提交任务的，但是它和execute()方法不同，它能够返回任务执行的结果，去看submit()方法的实现，会发现它实际上还是调用的execute()方法，只不过它利用了Future来获取任务执行结果（Future相关内容将在下一篇讲述）。  
　　shutdown()和shutdownNow()是用来关闭线程池的。\*

**代码示例**

package test;
 
 import java.io.IOException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 
 public class Test { 
 
 /** * @param args * @throws IOException */
 public static void main(String[] args) throws IOException {
 
 ExecutorService executorService = Executors.newCachedThreadPool();
 //第一种
 Thread t = new Thread(new Test2());
 
 executorService.execute(t);
 
 //第二种 有返回结果
 Thread t1 = new Thread(new Test3());
 
 Future<?> future=executorService.submit(t1);
 
 // 第三种
 executorService.submit(new Runnable() {
 public void run() {
 
 }
 });
 
 }
 
 }
 
 class Test2 implements Runnable {
 public void run() {
 
 }
 }
 
 class Test3 extends Thread {
 public void run() {
 
 }
 }