1. Java ThreadLocal ??

Java ThreadLocal? ????? ? ???? ????? ???? ?? ???? ???? ??? ??? ?????. ?? ? ???? ?? ??? ??? ??? ?? ??? ???? ?? ?????.

1.1 ThreadLocal?? ??????

ThreadLocal? ??? ?? ??? ???? Java ??????. ??? ??? ????? ? ???(get ?? set ???? ??)?? ??? ?? ?? ???? ????. ThreadLocal ????? ????? ??? ???? ????? ???? ??? ?? ?????.

1.2 ThreadLocal? ????? ???? ??

???? ???? ThreadLocal ??? ????? ThreadLocal ????? ?? ???? ?? ??? ? ???? ?????. ? ???? ??? ?? ???? ???? ?? ???? ???? ? ??? ???. ????? ThreadLocal? ?? ??? ???? ?? ?? ??? ?? ?? ?? ?? ?????.

1.3 ? ThreadLocal? ??????

ThreadLocal? ?? ???? ??? ????? ???? ??? ???? ? ? ??????. ?? ??? ?? ??, ?????? ?? ?? ??? ?? ????? ? ?? ?? ???? ?? ? ???? ??? ??? ??? ??? ?? ?????? ????? ?????.

1.4 ?: ??? ???? ThreadLocal ??

ThreadLocal? ???? ???? ???? ???? ??? ?? ???????.

public class ThreadLocalExample {
    private static ThreadLocal<Integer> threadLocalCounter = ThreadLocal.withInitial(() -> 0);

    public static void main(String[] args) {
        Runnable task = () -> {
            for (int i = 0; i < 5; i++) {
                threadLocalCounter.set(threadLocalCounter.get() + 1);
                System.out.println(Thread.currentThread().getName() + " - Counter: " + threadLocalCounter.get());
            }
        };

        Thread thread1 = new Thread(task, "Thread-1");
        Thread thread2 = new Thread(task, "Thread-2");

        thread1.start();
        thread2.start();
    }
}

1.5 ?? ??

? ??? ???? ? ???? ????? ?? ???? ????? ?? ? ? ????.

Thread-1 - Counter: 1
Thread-1 - Counter: 2
Thread-1 - Counter: 3
Thread-1 - Counter: 4
Thread-1 - Counter: 5
Thread-2 - Counter: 1
Thread-2 - Counter: 2
Thread-2 - Counter: 3
Thread-2 - Counter: 4
Thread-2 - Counter: 5

?? ? ???? ?? ???? ??? ?? ??? ???? ??? ??? ?????.

2. ThreadLocal? ?? ?? ??

ThreadLocal? ??? ????? ?? ?? ????. ??? ??? ?? ??? ?? ??? ?????? ??? ??????? ?????.

2.1 ? ???????? ThreadLocal ??

? ???????? ThreadLocal? ??? ?? ???? ? ?? ??? ?? ??? ?????? ??? ???? ? ?? ?????. ?:

public class ThreadLocalExample {
    private static ThreadLocal<Integer> threadLocalCounter = ThreadLocal.withInitial(() -> 0);

    public static void main(String[] args) {
        Runnable task = () -> {
            for (int i = 0; i < 5; i++) {
                threadLocalCounter.set(threadLocalCounter.get() + 1);
                System.out.println(Thread.currentThread().getName() + " - Counter: " + threadLocalCounter.get());
            }
        };

        Thread thread1 = new Thread(task, "Thread-1");
        Thread thread2 = new Thread(task, "Thread-2");

        thread1.start();
        thread2.start();
    }
}

? ?????? ??? ??? ???? ? ????? ??? User ??? ?? ? ???? ???? ?? ???? ??? ?? ????? ?? ?????.

2.2 ???? ??? ??? ??

ThreadLocal? ????? ??? ?? ?? ????. ???? ?? ? ??? ??? ?? ??? ???? ?? ????? ????. ?? ?? ?? ?? ?? ???????? ??? ??? ??? ? ????.

?? ????? ??? ?? ?? ? ?? ???? ??? ?? remove ???? ?????.

Thread-1 - Counter: 1
Thread-1 - Counter: 2
Thread-1 - Counter: 3
Thread-1 - Counter: 4
Thread-1 - Counter: 5
Thread-2 - Counter: 1
Thread-2 - Counter: 2
Thread-2 - Counter: 3
Thread-2 - Counter: 4
Thread-2 - Counter: 5

2.3 ?? ?: ?????? ?? ??

??? ThreadLocal? ???? ?????? ??? ???? ??? ????.

public class UserContext {
    private static ThreadLocal<User> currentUser = new ThreadLocal<>();

    public static void set(User user) {
        currentUser.set(user);
    }

    public static User get() {
        return currentUser.get();
    }

    public static void clear() {
        currentUser.remove();
    }
}

? ????? ?? ?????? ??? ?? ??? ? ??? ??? ?????.

3. ??

Java? ThreadLocal? ????? ???? ??? ?? ??? ???? ?? ??? ?????. ? ???? ???? ?? ???? ???? ??? ???? ?????. ??? ? ??? ? ??? ????. ??? ??? ????? ?? ThreadLocal ??? ???? ?? ?? ???.

ThreadLocal? ????? ???? ??? ?? ??? ??? ???? ?? ??? ??? ?? ??? ??? ?????!

?? ? ?? ???? ?????. Java ??? ??? ??? ?????? ??? ??? ?? ?? ?? ?? ?? ??

? ??? Java ??? ??? ??? ?????? ??? ??? ?? ?? ?? ?? ?? ???? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!