本文轉載自:原文鏈接
1、ThreadPool的優點 |
在Java.util.concurrent包下,提供了一系列與線程池相關的類。合理的使用線程池,可以帶來多個好處:
(1)降低資源消耗。通過重複利用已創建的線程降低線程創建和銷燬造成的消耗;
(2)提高響應速度。當任務到達時,任務可以不需要等到線程創建就能立即執行;
(3)提高線程的可管理性。線程是稀缺資源,如果無限制的創建,不僅會消耗系統資源,還會降低系統的穩定性,使用線程池可以進行統一的分配,調優和監控。
線程池可以應對突然大爆發量的訪問,通過有限個固定線程爲大量的操作服務,減少創建和銷燬線程所需的時間。
1、ThreadPool的創建 |
我們一般通過Executors類下的四個成員函數創建相應的線程池:
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//創建一個定時任務的線程池</span> ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//創建單線程的線程池</span> ExecutorService singleThreadPool = Executors.newSingleThreadExecutor(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//創建緩存線程池(重用先前的線程)</span> ExecutorService cachedThreadPool = Executors.newCachedThreadPool(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//創建一個帶有固定線程的線程池</span> ExecutorService threadPool = Executors.newFixedThreadPool(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>); </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>
我們可以從源碼看出,上面四個方法會調用ThreadPoolExecutor的構造方法創建線程池。
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> ExecutorService <span class="hljs-title" style="box-sizing: border-box;">newFixedThreadPool</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> nThreads) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ThreadPoolExecutor(nThreads, nThreads, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>L, TimeUnit.MILLISECONDS, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> LinkedBlockingQueue<Runnable>()); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>
創建一個ThreadPoolExecutor線程池一般需要以下幾個參數:
-
corePoolSize(線程池的基本大小):
當提交一個任務到線程池時,線程池會創建一個線程來執行任務,即使其他空閒的基本線程能夠執行新任務也會創建線程,等到需要執行的任務數大於線程池基本大小時就不再創建。如果調用了線程池的prestartAllCoreThreads方法,線程池會提前創建並啓動所有基本線程。
-
maximumPoolSize(線程池最大大小):
線程池允許創建的最大線程數。如果隊列滿了,並且已創建的線程數小於最大線程數,則線程池會再創建新的線程執行任務。值得注意的是如果使用了無界的任務隊列這個參數就沒什麼效果。
-
keepAliveTime(線程活動保持時間):
線程池的工作線程空閒後,保持存活的時間。所以如果任務很多,並且每個任務執行的時間比較短,可以調大這個時間,提高線程的利用率。 -
TimeUnit(線程活動保持時間的單位):
可選的單位有天(DAYS),小時(HOURS),分鐘(MINUTES),毫秒(MILLISECONDS)等。
-
workQueue(任務隊列):
用於保存等待執行的任務的阻塞隊列。 可以選擇以下幾個阻塞隊列:ArrayBlockingQueue、LinkedBlockingQueue、SynchronousQueue、PriorityBlockingQueue
- threadFactory:
用於設置創建線程的工廠,可以通過線程工廠給每個創建出來的線程設置更有意義的名字。
-
handler(飽和策略):
當隊列和線程池都滿了,說明線程池處於飽和狀態,那麼必須採取一種策略處理提交的新任務。這個策略默認情況下是AbortPolicy,表示無法處理新任務時拋出異常。我們儘量優先使用Executors提供的靜態方法來創建線程池,如果Executors提供的方法無法滿足要求,再自己通過ThreadPoolExecutor類來創建線程池。
2、向線程池提交任務 |
有兩種方式:
① 我們可以使用execute提交的任務,但是execute方法沒有返回值,所以無法判斷任務是否被線程池執行成功。通過以下代碼可知execute方法輸入的任務是一個Runnable類的實例。
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">threadsPool.execute(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO Auto-generated method stub</span> } });</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>
② 使用submit 方法來提交任務,它會返回一個future,那麼我們可以通過這個future來判斷任務是否執行成功,通過future的get方法來獲取返回值,get方法會阻塞住直到任務完成,而使用get(long timeout, TimeUnit unit)方法則會阻塞一段時間後立即返回,這時有可能任務沒有執行完。
<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Future<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span>> future = executor.submit(harReturnValuetask); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Object</span> s = future.get(); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 處理中斷異常</span> } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (ExecutionException e) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 處理無法執行任務異常</span> } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 關閉線程池</span> executor.shutdown(); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>
3、線程池的關閉 |
我們可以通過調用線程池(ExecutorService的對象)的shutdown或shutdownNow方法來關閉線程池,它們的原理是遍歷線程池中的工作線程,然後逐個調用線程的interrupt方法來中斷線程,所以無法響應中斷的任務可能永遠無法終止。但是它們存在一定的區別,shutdownNow首先將線程池的狀態設置成STOP,然後嘗試停止所有的正在執行或暫停任務的線程,並返回等待執行任務的列表,而shutdown只是將線程池的狀態設置成SHUTDOWN狀態,然後中斷所有沒有正在執行任務的線程。
只要調用了這兩個關閉方法的其中一個,isShutdown方法就會返回true。當所有的任務都已關閉後,才表示線程池關閉成功,這時調用isTerminaed方法會返回true。至於我們應該調用哪一種方法來關閉線程池,應該由提交到線程池的任務特性決定,通常調用shutdown來關閉線程池,如果任務不一定要執行完,則可以調用shutdownNow。
4、線程池的工作流程 |
從上圖我們可以看出,當提交一個新任務到線程池時,線程池的處理流程如下:
1、首先線程池判斷基本線程池是否已滿( corePoolSize )沒滿,創建一個工作線程來執行任務。滿了,則進入下個流程。
2、其次線程池判斷工作隊列是否已滿?沒滿,則將新提交的任務存儲在工作隊列裏。滿了,則進入下個流程。
3、最後線程池判斷整個線程池是否已滿(< maximumPoolSize ?)?沒滿,則創建一個新的工作線程來執行任務,滿了,則交給飽和策略來處理這個任務。
也就是說,線程池優先要創建出基本線程池大小(corePoolSize)的線程數量,沒有達到這個數量時,每次提交新任務都會直接創建一個新線程,當達到了基本線程數量後,又有新任務到達,優先放入等待隊列,如果隊列滿了,纔去創建新的線程(不能超過線程池的最大數maxmumPoolSize)。
線程池創建線程時,會將線程封裝成工作線程Worker,Worker在執行完任務後,還會無限循環獲取工作隊列裏的任務來執行。我們可以從Worker的run方法裏看到這點:
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { Runnable task = firstTask; firstTask = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (task != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> || (task = getTask()) != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) { runTask(task); task = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>; } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { workerDone(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>); } } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>
5、線程池的監控 |
通過繼承線程池並重寫線程池的beforeExecute,afterExecute和terminated方法,我們可以在任務執行前,執行後和線程池關閉前幹一些事情。如監控任務的平均執行時間,最大執行時間和最小執行時間等。這幾個方法在線程池裏是空方法。
6、線程池的例子 |
示例一:
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DifferentKindsThreadPool</span> {</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// displayScheduledThreadPool();</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// displaySingleThreadPool();</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// displayCachedThreadPool();</span> displayThreadPool(); } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 創建一個定時任務的線程池 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">displayScheduledThreadPool</span>() { ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//它可以向固定線程池一樣執行任務</span> distributeTaskForThreadPool(scheduledThreadPool); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//這是它的特殊之處,可以定時任務</span> scheduledThreadPool.schedule( <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"開始執行任務1"</span>); } }, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>, TimeUnit.SECONDS); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//每隔2秒再次重新執行任務</span> scheduledThreadPool.scheduleAtFixedRate( <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"開始執行任務2"</span>); } }, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>, TimeUnit.SECONDS); } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 創建只有一個線程的線程池,如果線程終止, * 他將會創建一個新的線程加入到池子中,這 * 個線程池會保證池子中始終有一個線程 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">displaySingleThreadPool</span>() { ExecutorService singleThreadPool = Executors.newSingleThreadExecutor(); distributeTaskForThreadPool(singleThreadPool); } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 創建一個可根據需要創建線程的線程池,但是 * 當先前創建的線程可得到時就會重用先前的線 * 程,如果不存在可得到的線程,一個新的線程 * 將被創建並被加入到池子中。60秒沒有被用到 * 的線程將被終止並從緩存中移除 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">displayCachedThreadPool</span>() { ExecutorService cachedThreadPool = Executors.newCachedThreadPool(); distributeTaskForThreadPool(cachedThreadPool); } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 創建一個帶有固定線程的線程池 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">displayThreadPool</span>() { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 創建一個帶有4個固定線程的線程池</span> ExecutorService threadPool = Executors.newFixedThreadPool(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>); distributeTaskForThreadPool(threadPool); } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 爲線程池分配8個任務,使其驅動 *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> threadPool */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">distributeTaskForThreadPool</span>(ExecutorService threadPool) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 讓線程池驅動8個任務</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>; i <= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>; i++) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 由於內部類裏面不能放一個非final的變量,所以我把i的值賦予task</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> task = i; threadPool.execute(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"我是"</span> + Thread.currentThread().getName() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">","</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"拿到了第"</span> + task + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"個任務,我開始執行了"</span>); } }); } } } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; 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padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; 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padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li></ul>
示例二:
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> BankCount { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> synchronized <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">addMoney</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> money){<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//存錢</span> System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">">存入:"</span> + money); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> synchronized <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">getMoney</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> money){<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//取錢</span> System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">">取錢:"</span> + money); } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> BankTest { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) { final BankCount bankCount = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> BankCount(); ExecutorService executor = Executors.newFixedThreadPool(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>); executor.execute(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//存錢線程</span> @Override <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span>(i-- > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>){ bankCount.addMoney(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) { e.printStackTrace(); } } } }); Future<?> future = executor.submit(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//取錢線程</span> @Override <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span>(i-- > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) { e.printStackTrace(); } bankCount.getMoney(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span>); } } }); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { Object res = future.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>(); System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(res); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 處理中斷異常</span> e.printStackTrace(); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (ExecutionException e) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 處理無法執行任務異常</span> e.printStackTrace(); }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span>{ <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 關閉線程池</span> executor.shutdown(); } } }</code>