轉發自
http://blog.csdn.net/paul342/article/details/52442932
Java通過Executors提供四種線程池，分別為：
newCachedThreadPool創建一個可緩存線程池，如果線程池長度超過處理需要，可靈活回收空閑線程，若無可回收，則新建線程。
newFixedThreadPool 創建一個定長線程池，可控制線程最大并發數，超出的線程會在隊列中等待。
newScheduledThreadPool 創建一個定長線程池，支持定時及周期性任務執行。
newSingleThreadExecutor 創建一個單線程化的線程池，它只會用唯一的工作線程來執行任務，保證所有任務按照指定順序(FIFO, LIFO, 優先級)執行。
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(1) newCachedThreadPool
創建一個可緩存線程池，如果線程池長度超過處理需要，可靈活回收空閑線程，若無可回收，則新建線程。示例代碼如下：
?1?package?test;??
?2?import?java.util.concurrent.ExecutorService;??
?3?import?java.util.concurrent.Executors;??
?4?public?class?ThreadPoolExecutorTest?{??
?5??public?static?void?main(String[]?args)?{??
?6???ExecutorService?cachedThreadPool?=?Executors.newCachedThreadPool();??
?7???for?(int?i?=?0;?i?<?10;?i++)?{??
?8????final?int?index?=?i;??
?9????try?{??
10?????Thread.sleep(index?*?1000);??
11????}?catch?(InterruptedException?e)?{??
12?????e.printStackTrace();??
13????}??
14????cachedThreadPool.execute(new?Runnable()?{??
15?????public?void?run()?{??
16??????System.out.println(index);??
17?????}??
18????});??
19???}??
20??}??
21?}?
線程池為無限大，當執行第二個任務時第一個任務已經完成，會復用執行第一個任務的線程，而不用每次新建線程。
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(2) newFixedThreadPool
創建一個定長線程池，可控制線程最大并發數，超出的線程會在隊列中等待。示例代碼如下：
?1?????package?test;??
?2?????import?java.util.concurrent.ExecutorService;??
?3?????import?java.util.concurrent.Executors;??
?4?????public?class?ThreadPoolExecutorTest?{??
?5??????public?static?void?main(String[]?args)?{??
?6???????ExecutorService?fixedThreadPool?=?Executors.newFixedThreadPool(3);??
?7???????for?(int?i?=?0;?i?<?10;?i++)?{??
?8????????final?int?index?=?i;??
?9????????fixedThreadPool.execute(new?Runnable()?{??
10?????????public?void?run()?{??
11??????????try?{??
12???????????System.out.println(index);??
13???????????Thread.sleep(2000);??
14??????????}?catch?(InterruptedException?e)?{??
15???????????e.printStackTrace();??
16??????????}??
17?????????}??
18????????});??
19???????}??
20??????}??
21?????}??
因為線程池大小為3，每個任務輸出index后sleep 2秒，所以每兩秒打印3個數字。
定長線程池的大小最好根據系統資源進行設置。如Runtime.getRuntime().availableProcessors()
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(3)? newScheduledThreadPool
創建一個定長線程池，支持定時及周期性任務執行。延遲執行示例代碼如下：
?1?????package?test;??
?2?????import?java.util.concurrent.Executors;??
?3?????import?java.util.concurrent.ScheduledExecutorService;??
?4?????import?java.util.concurrent.TimeUnit;??
?5?????public?class?ThreadPoolExecutorTest?{??
?6??????public?static?void?main(String[]?args)?{??
?7???????ScheduledExecutorService?scheduledThreadPool?=?Executors.newScheduledThreadPool(5);??
?8???????scheduledThreadPool.schedule(new?Runnable()?{??
?9????????public?void?run()?{??
10?????????System.out.println("delay?3?seconds");??
11????????}??
12???????},?3,?TimeUnit.SECONDS);??
13??????}??
14?????}??
表示延遲3秒執行。
定期執行示例代碼如下：
?1?????package?test;??
?2?????import?java.util.concurrent.Executors;??
?3?????import?java.util.concurrent.ScheduledExecutorService;??
?4?????import?java.util.concurrent.TimeUnit;??
?5?????public?class?ThreadPoolExecutorTest?{??
?6??????public?static?void?main(String[]?args)?{??
?7???????ScheduledExecutorService?scheduledThreadPool?=?Executors.newScheduledThreadPool(5);??
?8???????scheduledThreadPool.scheduleAtFixedRate(new?Runnable()?{??
?9????????public?void?run()?{??
10?????????System.out.println("delay?1?seconds,?and?excute?every?3?seconds");??
11????????}??
12???????},?1,?3,?TimeUnit.SECONDS);??
13??????}??
14?????}??
表示延遲1秒后每3秒執行一次。
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(4) newSingleThreadExecutor
創建一個單線程化的線程池，它只會用唯一的工作線程來執行任務，保證所有任務按照指定順序(FIFO, LIFO, 優先級)執行。示例代碼如下：
?1?package?test;??
?2?import?java.util.concurrent.ExecutorService;??
?3?import?java.util.concurrent.Executors;??
?4?public?class?ThreadPoolExecutorTest?{??
?5??public?static?void?main(String[]?args)?{??
?6???ExecutorService?singleThreadExecutor?=?Executors.newSingleThreadExecutor();??
?7???for?(int?i?=?0;?i?<?10;?i++)?{??
?8????final?int?index?=?i;??
?9????singleThreadExecutor.execute(new?Runnable()?{??
10?????public?void?run()?{??
11??????try?{??
12???????System.out.println(index);??
13???????Thread.sleep(2000);??
14??????}?catch?(InterruptedException?e)?{??
15???????e.printStackTrace();??
16??????}??
17?????}??
18????});??
19???}??
20??}??
21?}?
結果依次輸出，相當于順序執行各個任務。
你可以使用JDK自帶的監控工具來監控我們創建的線程數量，運行一個不終止的線程，創建指定量的線程，來觀察：
工具目錄：C:\Program Files\Java\jdk1.6.0_06\bin\jconsole.exe
運行程序做稍微修改：
?1?????package?test;??
?2?????import?java.util.concurrent.ExecutorService;??
?3?????import?java.util.concurrent.Executors;??
?4?????public?class?ThreadPoolExecutorTest?{??
?5??????public?static?void?main(String[]?args)?{??
?6???????ExecutorService?singleThreadExecutor?=?Executors.newCachedThreadPool();??
?7???????for?(int?i?=?0;?i?<?100;?i++)?{??
?8????????final?int?index?=?i;??
?9????????singleThreadExecutor.execute(new?Runnable()?{??
10?????????public?void?run()?{??
11??????????try?{??
12???????????while(true)?{??
13????????????System.out.println(index);??
14????????????Thread.sleep(10?*?1000);??
15???????????}??
16??????????}?catch?(InterruptedException?e)?{??
17???????????e.printStackTrace();??
18??????????}??
19?????????}??
20????????});??
21????????try?{??
22?????????Thread.sleep(500);??
23????????}?catch?(InterruptedException?e)?{??
24?????????e.printStackTrace();??
25????????}??
26???????}??
27??????}??
28?????}??
效果如下：
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選擇我們運行的程序：
監控運行狀態