參考：

http://curious.iteye.com/blog/2298849

網上有很多Executors的例子，但有些寫的非常草率，都只是寫如何建立，但有些沒有附上關閉方法。

Executors作為區域性變數時，建立了執行緒，一定要記得呼叫executor.shutdown();來關閉執行緒池，如果不關閉，會有執行緒洩漏問題。

如下有問題的程式碼：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestThread {

    public static void main(String[] args) {
        while (true) {
            try {
                ExecutorService service = Executors.newFixedThreadPool(1);
                service.submit(new Runnable() {
                    public void run() {
                        try {
                            Thread.sleep(2000);
                        } catch (InterruptedException e) {
                        }
                    }
                });
                service = null;
            } catch (Exception e) {
            }
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
            }
        }
    }

}
 

執行後，檢視jvm，會發現執行緒每2秒就增長一個。

加了shutdown程式碼後，就一直很平穩。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestThread {

    public static void main(String[] args) {
        while (true) {
            ExecutorService service = Executors.newFixedThreadPool(1);
            try {
                service.submit(new Runnable() {
                    public void run() {
                        try {
                            Thread.sleep(2000);
                        } catch (InterruptedException e) {
                        }
                    }
                });
            } catch (Exception e) {
            }finally{
                service.shutdown();
            }
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
            }
        }
    }

}