感谢博主的这篇分享，见 

在今天的面试中，突然被考官问了这个问题，当时脱口而出的是 threadlocal容易会有内存泄漏，需要注意remove。其实自己仔细想想，这个回答太过于结果了，没有思考为何要配合线程池的时候，去remove。

 

注意，这里需要你的jdk版本为1.8及以上，否者清将lambda表达式改为匿名内部类

 

问题的版本

1 public class ThreadLocalAndPool { 2  3     /** 4      * jdk8 的语法 5      */ 6     private static ThreadLocal
     
       variableLocal = ThreadLocal.withInitial(() -> 0); 7  8     public static int get() { 9         return variableLocal.get();10     }11 12     public static void remove() {13         variableLocal.remove();14     }15 16     public static void increment() {17         variableLocal.set(variableLocal.get() + 1);18     }19 20     public static void main(String[] args) {21         ExecutorService executorService = new ThreadPoolExecutor(2,2,0, TimeUnit.SECONDS,new LinkedBlockingDeque<>(12));22 23         for(int i=0;i<5;i++){24             executorService.execute(()->{25                 long threadId = Thread.currentThread().getId();26 27                 int before = get();28                 increment();29                 int after = get();30                 System.out.println("threadid " + threadId +"  before " + before + ", after " + after);31             });32         }33 34         executorService.shutdown();35     }36 37 38 }
     

得到的结果

threadid 12 before 0, after 1

threadid 13 before 0, after 1

threadid 12 before 1, after 2

threadid 13 before 1, after 2

threadid 12 before 2, after 3

 

这个其实就是threadlocal与线程池使用的问题了，因为threadlocal维护是 Map<Thread,T>这个结构，而线程池是对线程进行复用的，如果没有及时的清理，那么之前对该线程的使用，就会影响到后面的线程了，造成数据不准确。

 

修正的版本，就是加一个remove

1 public class ThreadLocalAndPool { 2  3     /** 4      * jdk8 的语法 5      */ 6     private static ThreadLocal
     
       variableLocal = ThreadLocal.withInitial(() -> 0); 7  8     public static int get() { 9         return variableLocal.get();10     }11 12     public static void remove() {13         variableLocal.remove();14     }15 16     public static void increment() {17         variableLocal.set(variableLocal.get() + 1);18     }19 20     public static void main(String[] args) {21         ExecutorService executorService = new ThreadPoolExecutor(2,2,0, TimeUnit.SECONDS,new LinkedBlockingDeque<>(12));22 23         for(int i=0;i<5;i++){24             executorService.execute(()->{25                 try {26                     long threadId = Thread.currentThread().getId();27 28                     int before = get();29                     increment();30                     int after = get();31                     System.out.println("threadid " + threadId +"  before " + before + ", after " + after);32                 }33                 finally {34                     remove();35                 }36             });37         }38 39         executorService.shutdown();40     }41 42 43 }
     

上面运行的结果如下（不同机器的threadid会有所不同）

threadid 12 before 0, after 1

threadid 13 before 0, after 1

threadid 12 before 0, after 1

threadid 13 before 0, after 1

threadid 13 before 0, after 1