threadlocal

ThreadLocal 是 Java 中的一个类，它可以在多线程环境下提供线程本地变量。它的作用是为每个线程提供一个独立的变量副本，这样每个线程都可以独立地改变自己的副本，而不会影响其他线程的副本。通常情况下，我们使用 ThreadLocal 来存储一些与线程有关的上下文信息，如用户身份信息、事务上下文等。

ThreadLocal 内部实现了一个 Map，用于存储不同线程的变量副本，Map 的 key 是线程对象，value 是变量副本。在使用时，我们可以通过 ThreadLocal 的 get() 方法获取当前线程对应的变量副本，也可以通过 set() 方法设置当前线程的变量副本。由于每个线程都有自己的变量副本，因此不会出现线程安全问题。

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Threadlocal

ThreadLocal is a class in Java that is used to create thread-local variables. These variables are stored separately for each thread and can only be accessed by that thread. This means that changes made to the variable by one thread do not affect the value of the variable in other threads.

ThreadLocal is often used in multi-threaded applications where multiple threads access the same object or resource. By using ThreadLocal, each thread can have its own copy of the object or resource, which avoids conflicts and synchronization issues.

To use ThreadLocal, you create an instance of the class and then call its methods to set and get the thread-local value. For example, to create a thread-local variable of type Integer, you would do the following:

ThreadLocal<Integer> myThreadLocal = new ThreadLocal<Integer>();

// Set the thread-local value for the current thread
myThreadLocal.set(42);

// Get the thread-local value for the current thread
Integer myValue = myThreadLocal.get();

In this example, each thread would have its own copy of the Integer value, and changes made to the value by one thread would not affect the value in other threads.