ThreadPoolTaskExecutor

继我们之前聊到了 踩坑之SimpleAsyncTaskExecutor

那我们可以使用什么类来替代此类实现上下文的传递呢？

ThreadPoolTaskExecutor

1. 我们通过TaskDecorator接口反查，可以发现ThreadPoolTaskExecutor类也在使用这个接口；我们通过这个类申明一个Bean：

    @Bean("taskExecutor")
    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(Math.min(16, Runtime.getRuntime().availableProcessors() * 2));
        executor.setMaxPoolSize(executor.getCorePoolSize() * 2);
        executor.setThreadNamePrefix("async-");
        executor.setTaskDecorator(runnable -> {
            SecurityContext context = SecurityContextHolder.getContext();
            return () -> {
                try {
                    SecurityContextHolder.setContext(context);
                    runnable.run();
                } finally {
                    SecurityContextHolder.clearContext();
                }
            };
        });
        executor.initialize();
        return executor;
    }

在对一系列属性设置之后，通过initialize方法完成初始化；

2. 看下初始化方法内部做了什么？

	@Nullable
	// 内部维护了ExecutorService
	private ExecutorService executor;

	public void initialize() {
		if (logger.isInfoEnabled()) {
			logger.info("Initializing ExecutorService" + (this.beanName != null ? " '" + this.beanName + "'" : ""));
		}
       	// 设置线程名字
		if (!this.threadNamePrefixSet && this.beanName != null) {
			setThreadNamePrefix(this.beanName + "-");
		}
        // 又执行了initializeExecutor
		this.executor = initializeExecutor(this.threadFactory, this.rejectedExecutionHandler);
	}

看下initializeExecutor

	protected ExecutorService initializeExecutor(
			ThreadFactory threadFactory, RejectedExecutionHandler rejectedExecutionHandler) {
		// 创建队列
		BlockingQueue<Runnable> queue = createQueue(this.queueCapacity);
		// 定义线程池
		ThreadPoolExecutor executor;
        // 如果实现了装饰接口
		if (this.taskDecorator != null) {
            // new了一个正常的线程池，区别是重写了execute方法
			executor = new ThreadPoolExecutor(
					this.corePoolSize, this.maxPoolSize, this.keepAliveSeconds, TimeUnit.SECONDS,
					queue, threadFactory, rejectedExecutionHandler) {
				@Override
				public void execute(Runnable command) {
                    // 重写execute方法， 首先执行了装饰接口实现
					Runnable decorated = taskDecorator.decorate(command);
					if (decorated != command) {
                        // 放到弱引用的map中，与此文无关，暂不赘述
						decoratedTaskMap.put(decorated, command);
					}
                    // 执行线程池的execute方法
					super.execute(decorated);
				}
			};
		}
		else {
			executor = new ThreadPoolExecutor(
					this.corePoolSize, this.maxPoolSize, this.keepAliveSeconds, TimeUnit.SECONDS,
					queue, threadFactory, rejectedExecutionHandler);

		}

		if (this.allowCoreThreadTimeOut) {
			executor.allowCoreThreadTimeOut(true);
		}

		this.threadPoolExecutor = executor;
		return executor;
	}

3. 其实在SimpleAsyncTaskExecutor类中作者也标识了这个类：

    *
    * @author Juergen Hoeller
    * @since 2.0
    * @see #setConcurrencyLimit
    * @see SyncTaskExecutor
    * @see org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor   标识了这个类
    * @see org.springframework.scheduling.commonj.WorkManagerTaskExecutor
    */
   @SuppressWarnings("serial")
   public class SimpleAsyncTaskExecutor extends CustomizableThreadCreator