Java线程池技术

╰+攻爆jí腚メ 2022-07-13 06:47 281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

  1. public static ExecutorService newCachedThreadPool() {
  2.         return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
  3.                                       60L, TimeUnit.SECONDS,
  4.                                       new SynchronousQueue<Runnable>());
  5.     }
  7. public ThreadPoolExecutor(int corePoolSize,
  8.                               int maximumPoolSize,
  9.                               long keepAliveTime,
  10.                               TimeUnit unit,
  11.                               BlockingQueue<Runnable> workQueue,
  12.                               ThreadFactory threadFactory,
  13.                               RejectedExecutionHandler handler) {
  14.         if (corePoolSize < 0 ||
  15.             maximumPoolSize <= 0 ||
  16.             maximumPoolSize < corePoolSize ||
  17.             keepAliveTime < 0)
  18.             throw new IllegalArgumentException();
  19.         if (workQueue == null || threadFactory == null || handler == null)
  20.             throw new NullPointerException();
  21.         this.corePoolSize = corePoolSize;
  22.         this.maximumPoolSize = maximumPoolSize;
  23.         this.workQueue = workQueue;
  24.         this.keepAliveTime = unit.toNanos(keepAliveTime);
  25.         this.threadFactory = threadFactory;
  26.         this.handler = handler;
  27.     }

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。

  1. /* * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */
  3. /* * * * * * * 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/ */
  5. package java.util.concurrent;
  6. import java.util.*;
  7. import java.util.concurrent.atomic.AtomicInteger;
  8. import java.security.AccessControlContext;
  9. import java.security.AccessController;
  10. import java.security.PrivilegedAction;
  11. import java.security.PrivilegedExceptionAction;
  12. import java.security.PrivilegedActionException;
  13. import java.security.AccessControlException;
  14. import sun.security.util.SecurityConstants;
  16. /** * 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 */
  17. public class Executors { 
  19.     /** * 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} */
  20.     public static ExecutorService newFixedThreadPool(int nThreads) {
  21.         return new ThreadPoolExecutor(nThreads, nThreads,
  22.                                       0L, TimeUnit.MILLISECONDS,
  23.                                       new LinkedBlockingQueue<Runnable>());
  24.     }
  26.     /** * 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} */
  27.     public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
  28.         return new ThreadPoolExecutor(nThreads, nThreads,
  29.                                       0L, TimeUnit.MILLISECONDS,
  30.                                       new LinkedBlockingQueue<Runnable>(),
  31.                                       threadFactory);
  32.     }
  34.     /** * 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 */
  35.     public static ExecutorService newSingleThreadExecutor() {
  36.         return new FinalizableDelegatedExecutorService
  37.             (new ThreadPoolExecutor(1, 1,
  38.                                     0L, TimeUnit.MILLISECONDS,
  39.                                     new LinkedBlockingQueue<Runnable>()));
  40.     }
  42.     /** * 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 */
  43.     public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
  44.         return new FinalizableDelegatedExecutorService
  45.             (new ThreadPoolExecutor(1, 1,
  46.                                     0L, TimeUnit.MILLISECONDS,
  47.                                     new LinkedBlockingQueue<Runnable>(),
  48.                                     threadFactory));
  49.     }
  51.     /** * 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 */
  52.     public static ExecutorService newCachedThreadPool() {
  53.         return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
  54.                                       60L, TimeUnit.SECONDS,
  55.                                       new SynchronousQueue<Runnable>());
  56.     }
  58.     /** * 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 */
  59.     public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
  60.         return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
  61.                                       60L, TimeUnit.SECONDS,
  62.                                       new SynchronousQueue<Runnable>(),
  63.                                       threadFactory);
  64.     }
  66.     /** * 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 */
  67.     public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
  68.         return new DelegatedScheduledExecutorService
  69.             (new ScheduledThreadPoolExecutor(1));
  70.     }
  72.     /** * 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 */
  73.     public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
  74.         return new DelegatedScheduledExecutorService
  75.             (new ScheduledThreadPoolExecutor(1, threadFactory));
  76.     }
  78.     /** * 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} */
  79.     public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
  80.         return new ScheduledThreadPoolExecutor(corePoolSize);
  81.     }
  83.     /** * 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 */
  84.     public static ScheduledExecutorService newScheduledThreadPool(
  85.             int corePoolSize, ThreadFactory threadFactory) {
  86.         return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
  87.     }
  90.     /** * 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 */
  91.     public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
  92.         if (executor == null)
  93.             throw new NullPointerException();
  94.         return new DelegatedExecutorService(executor);
  95.     }
  97.     /** * 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 */
  98.     public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
  99.         if (executor == null)
  100.             throw new NullPointerException();
  101.         return new DelegatedScheduledExecutorService(executor);
  102.     }
  104.     /** * 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 * <em>pool-N-thread-M</em>, where <em>N</em> is the sequence * number of this factory, and <em>M</em> is the sequence number * of the thread created by this factory. * @return a thread factory */
  105.     public static ThreadFactory defaultThreadFactory() {
  106.         return new DefaultThreadFactory();
  107.     }
  109.     /** * 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. * * <p> 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. */
  110.     public static ThreadFactory privilegedThreadFactory() {
  111.         return new PrivilegedThreadFactory();
  112.     }
  114.     /** * 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 */
  115.     public static <T> Callable<T> callable(Runnable task, T result) {
  116.         if (task == null)
  117.             throw new NullPointerException();
  118.         return new RunnableAdapter<T>(task, result);
  119.     }
  121.     /** * 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 */
  122.     public static Callable<Object> callable(Runnable task) {
  123.         if (task == null)
  124.             throw new NullPointerException();
  125.         return new RunnableAdapter<Object>(task, null);
  126.     }
  128.     /** * 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 */
  129.     public static Callable<Object> callable(final PrivilegedAction<?> action) {
  130.         if (action == null)
  131.             throw new NullPointerException();
  132.         return new Callable<Object>() {
  133.             public Object call() { return action.run(); }};
  134.     }
  136.     /** * 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 */
  137.     public static Callable<Object> callable(final PrivilegedExceptionAction<?> action) {
  138.         if (action == null)
  139.             throw new NullPointerException();
  140.         return new Callable<Object>() {
  141.             public Object call() throws Exception { return action.run(); }};
  142.     }
  144.     /** * 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 * */
  145.     public static <T> Callable<T> privilegedCallable(Callable<T> callable) {
  146.         if (callable == null)
  147.             throw new NullPointerException();
  148.         return new PrivilegedCallable<T>(callable);
  149.     }
  151.     /** * 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. */
  152.     public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> callable) {
  153.         if (callable == null)
  154.             throw new NullPointerException();
  155.         return new PrivilegedCallableUsingCurrentClassLoader<T>(callable);
  156.     }
  158.     // Non-public classes supporting the public methods
  160.     /** * A callable that runs given task and returns given result */
  161.     static final class RunnableAdapter<T> implements Callable<T> {
  162.         final Runnable task;
  163.         final T result;
  164.         RunnableAdapter(Runnable task, T result) {
  165.             this.task = task;
  166.             this.result = result;
  167.         }
  168.         public T call() {
  169.             task.run();
  170.             return result;
  171.         }
  172.     }
  174.     /** * A callable that runs under established access control settings */
  175.     static final class PrivilegedCallable<T> implements Callable<T> {
  176.         private final Callable<T> task;
  177.         private final AccessControlContext acc;
  179.         PrivilegedCallable(Callable<T> task) {
  180.             this.task = task;
  181.             this.acc = AccessController.getContext();
  182.         }
  184.         public T call() throws Exception {
  185.             try {
  186.                 return AccessController.doPrivileged(
  187.                     new PrivilegedExceptionAction<T>() {
  188.                         public T run() throws Exception {
  189.                             return task.call();
  190.                         }
  191.                     }, acc);
  192.             } catch (PrivilegedActionException e) {
  193.                 throw e.getException();
  194.             }
  195.         }
  196.     }
  198.     /** * A callable that runs under established access control settings and * current ClassLoader */
  199.     static final class PrivilegedCallableUsingCurrentClassLoader<T> implements Callable<T> {
  200.         private final Callable<T> task;
  201.         private final AccessControlContext acc;
  202.         private final ClassLoader ccl;
  204.         PrivilegedCallableUsingCurrentClassLoader(Callable<T> task) {
  205.             SecurityManager sm = System.getSecurityManager();
  206.             if (sm != null) {
  207.                 // Calls to getContextClassLoader from this class
  208.                 // never trigger a security check, but we check
  209.                 // whether our callers have this permission anyways.
  210.                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
  212.                 // Whether setContextClassLoader turns out to be necessary
  213.                 // or not, we fail fast if permission is not available.
  214.                 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
  215.             }
  216.             this.task = task;
  217.             this.acc = AccessController.getContext();
  218.             this.ccl = Thread.currentThread().getContextClassLoader();
  219.         }
  221.         public T call() throws Exception {
  222.             try {
  223.                 return AccessController.doPrivileged(
  224.                     new PrivilegedExceptionAction<T>() {
  225.                         public T run() throws Exception {
  226.                             Thread t = Thread.currentThread();
  227.                             ClassLoader cl = t.getContextClassLoader();
  228.                             if (ccl == cl) {
  229.                                 return task.call();
  230.                             } else {
  231.                                 t.setContextClassLoader(ccl);
  232.                                 try {
  233.                                     return task.call();
  234.                                 } finally {
  235.                                     t.setContextClassLoader(cl);
  236.                                 }
  237.                             }
  238.                         }
  239.                     }, acc);
  240.             } catch (PrivilegedActionException e) {
  241.                 throw e.getException();
  242.             }
  243.         }
  244.     }
  246.     /** * The default thread factory */
  247.     static class DefaultThreadFactory implements ThreadFactory {
  248.         private static final AtomicInteger poolNumber = new AtomicInteger(1);
  249.         private final ThreadGroup group;
  250.         private final AtomicInteger threadNumber = new AtomicInteger(1);
  251.         private final String namePrefix;
  253.         DefaultThreadFactory() {
  254.             SecurityManager s = System.getSecurityManager();
  255.             group = (s != null) ? s.getThreadGroup() :
  256.                                   Thread.currentThread().getThreadGroup();
  257.             namePrefix = "pool-" +
  258.                           poolNumber.getAndIncrement() +
  259.                          "-thread-";
  260.         }
  262.         public Thread newThread(Runnable r) {
  263.             Thread t = new Thread(group, r,
  264.                                   namePrefix + threadNumber.getAndIncrement(),
  265.                                   0);
  266.             if (t.isDaemon())
  267.                 t.setDaemon(false);
  268.             if (t.getPriority() != Thread.NORM_PRIORITY)
  269.                 t.setPriority(Thread.NORM_PRIORITY);
  270.             return t;
  271.         }
  272.     }
  274.     /** * Thread factory capturing access control context and class loader */
  275.     static class PrivilegedThreadFactory extends DefaultThreadFactory {
  276.         private final AccessControlContext acc;
  277.         private final ClassLoader ccl;
  279.         PrivilegedThreadFactory() {
  280.             super();
  281.             SecurityManager sm = System.getSecurityManager();
  282.             if (sm != null) {
  283.                 // Calls to getContextClassLoader from this class
  284.                 // never trigger a security check, but we check
  285.                 // whether our callers have this permission anyways.
  286.                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
  288.                 // Fail fast
  289.                 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
  290.             }
  291.             this.acc = AccessController.getContext();
  292.             this.ccl = Thread.currentThread().getContextClassLoader();
  293.         }
  295.         public Thread newThread(final Runnable r) {
  296.             return super.newThread(new Runnable() {
  297.                 public void run() {
  298.                     AccessController.doPrivileged(new PrivilegedAction<Void>() {
  299.                         public Void run() {
  300.                             Thread.currentThread().setContextClassLoader(ccl);
  301.                             r.run();
  302.                             return null;
  303.                         }
  304.                     }, acc);
  305.                 }
  306.             });
  307.         }
  308.     }
  310.     /** * A wrapper class that exposes only the ExecutorService methods * of an ExecutorService implementation. */
  311.     static class DelegatedExecutorService extends AbstractExecutorService {
  312.         private final ExecutorService e;
  313.         DelegatedExecutorService(ExecutorService executor) { e = executor; }
  314.         public void execute(Runnable command) { e.execute(command); }
  315.         public void shutdown() { e.shutdown(); }
  316.         public List<Runnable> shutdownNow() { return e.shutdownNow(); }
  317.         public boolean isShutdown() { return e.isShutdown(); }
  318.         public boolean isTerminated() { return e.isTerminated(); }
  319.         public boolean awaitTermination(long timeout, TimeUnit unit)
  320.             throws InterruptedException {
  321.             return e.awaitTermination(timeout, unit);
  322.         }
  323.         public Future<?> submit(Runnable task) {
  324.             return e.submit(task);
  325.         }
  326.         public <T> Future<T> submit(Callable<T> task) {
  327.             return e.submit(task);
  328.         }
  329.         public <T> Future<T> submit(Runnable task, T result) {
  330.             return e.submit(task, result);
  331.         }
  332.         public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
  333.             throws InterruptedException {
  334.             return e.invokeAll(tasks);
  335.         }
  336.         public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
  337.                                              long timeout, TimeUnit unit)
  338.             throws InterruptedException {
  339.             return e.invokeAll(tasks, timeout, unit);
  340.         }
  341.         public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
  342.             throws InterruptedException, ExecutionException {
  343.             return e.invokeAny(tasks);
  344.         }
  345.         public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
  346.                                long timeout, TimeUnit unit)
  347.             throws InterruptedException, ExecutionException, TimeoutException {
  348.             return e.invokeAny(tasks, timeout, unit);
  349.         }
  350.     }
  352.     static class FinalizableDelegatedExecutorService
  353.         extends DelegatedExecutorService {
  354.         FinalizableDelegatedExecutorService(ExecutorService executor) {
  355.             super(executor);
  356.         }
  357.         protected void finalize() {
  358.             super.shutdown();
  359.         }
  360.     }
  362.     /** * A wrapper class that exposes only the ScheduledExecutorService * methods of a ScheduledExecutorService implementation. */
  363.     static class DelegatedScheduledExecutorService
  364.             extends DelegatedExecutorService
  365.             implements ScheduledExecutorService {
  366.         private final ScheduledExecutorService e;
  367.         DelegatedScheduledExecutorService(ScheduledExecutorService executor) {
  368.             super(executor);
  369.             e = executor;
  370.         }
  371.         public ScheduledFuture<?> schedule(Runnable command, long delay,  TimeUnit unit) {
  372.             return e.schedule(command, delay, unit);
  373.         }
  374.         public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
  375.             return e.schedule(callable, delay, unit);
  376.         }
  377.         public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay,  long period, TimeUnit unit) {
  378.             return e.scheduleAtFixedRate(command, initialDelay, period, unit);
  379.         }
  380.         public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay,  long delay, TimeUnit unit) {
  381.             return e.scheduleWithFixedDelay(command, initialDelay, delay, unit);
  382.         }
  383.     }
  386.     /** Cannot instantiate. */
  387.     private Executors() {}
  388. }

*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

  1. package test;
  3. import java.io.IOException;
  4. import java.util.concurrent.ExecutorService;
  5. import java.util.concurrent.Executors;
  6. import java.util.concurrent.Future;
  8. public class Test { 
  10.     /** * @param args * @throws IOException */
  11.     public static void main(String[] args) throws IOException {
  13.         ExecutorService executorService = Executors.newCachedThreadPool();
  14.          //第一种
  15.         Thread t = new Thread(new Test2());
  17.         executorService.execute(t);
  19.         //第二种 有返回结果
  20.         Thread t1 = new Thread(new Test3());
  22.         Future<?> future=executorService.submit(t1);
  24.         // 第三种
  25.         executorService.submit(new Runnable() {
  26.             public void run() {
  28.             }
  29.         });
  31.     }
  33. }
  35. class Test2 implements Runnable {
  36.     public void run() {
  38.     }
  39. }
  41. class Test3 extends Thread {
  42.     public void run() {
  44.     }
  45. }

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