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ThreadLocal的底层原理

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作者 deathwhispers
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ThreadLocal的底层原理

  1. ThreadLocal是Java中所提供的线程本地存储机制，可以利用该机制将数据缓存在某个线程内部，该线程可以在任意时刻、任意方法中获取缓存的数据
  2. ThreadLocal底层通过ThreadLocalMap来实现的，每个Thread对象（并不是ThreadLocal对象）中都存在一个ThreadLocalMap，Map的key为ThreadLocal对象，Map的value为需要缓存的值。
  3. 如果在线程池中使用ThreadLocal会造成内存泄露，因为当ThreadLocal对象使用完之后，应该要把设置的key、value（也就是Entry对象）进行回收，但是线程池中的线程不会回收，而线程对象是通过强引用指向ThreadLocalMap，ThreadLocalMap也是通过强引用指向Entry对象，线程不被回收，Entry对象也就不会回收，从而出现内存泄露，解决办法是：在使用ThreadLocal对象之后，手动调用ThreadLocal的remove方法，手动清除对象
  4. ThreadLocal经典的应用场景就是连接管理（一个线程持有一个连接，该连接对象可以在不同的方法之间进行传递，线程之间不共享同一个连接）

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threadlocal
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