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This "ThreadLocal in java can do" article, the article sample code is introduced in great detail, with a certain reference value, interested friends must refer to, for "what can ThreadLocal in java do", Xiaobian sorted out the following knowledge points, please follow the pace of the editor step by step slowly understand, then let us enter the topic.

What is ThreadLocal? What can it do?

Before we elaborate on ThreadLocal, let's take a look at how its designers describe ThreadLocal.

After reading the official description, combined with my own understanding, ThreadLocal provides a data access mechanism corresponding to independent threads, which realizes the ability to isolate variables between threads and obtain or set variables independently during the thread life cycle. ThreadLocal can come in handy if we want to pass parameters within a thread but do not want to be used as method parameters. It is worth noting, however, that ThreadLocal does not solve the problem of variable sharing. In fact, from the name of ThreadLocal, thread-local variables have also roughly explained its role, so variable naming is still very important, as the name implies. If you feel that you don't quite understand, it doesn't matter, we can deepen our understanding through the following scenarios.

If there is the following scenario, if there is only one database connection, clients 1, 2, and 3 all need to obtain a database connection to perform specific database operations, but only one thread can obtain the connection at a time, and other threads can only wait. Therefore, there will be the problem of inefficient database access.

Is there anything we can do to avoid thread waiting? The root cause of the above problem is that the database connection is a shared variable and a colleague can only have one thread to operate on. If all three threads have their own database connections and are isolated from each other, there will be no problem of waiting. So at this point we can use ThreadLocal to achieve variable isolation in different threads. It can be seen that ThreadLocal is a way of exchanging space for time.

The Secret of ThreadLocal implementing Thread isolation

From the above, we learned that ThreadLocal can achieve thread-level isolation of variable access. So how on earth did it come true? This also requires the combination of Thread and ThreadLocal source code analysis in order to unravel the mystery of ThreadLocal thread isolation.

Public class Thread implements Runnable {. / * ThreadLocal values pertaining to this thread. This map is maintained * by the ThreadLocal class. * / ThreadLocal.ThreadLocalMap threadLocals = null;.}

In the Thread source code, we found that it has a threadLocals variable, and its type is the inner class ThreadLocalMap in ThreadLocal. Let's take a look at the definition of ThreadLocalMap. We can see from the source code that ThreadLocalMap is actually an array of Entry, the key corresponding to this Entry is actually an instance of ThreadLocal, and value is the actual variable value.

Public class ThreadLocal {... Static class ThreadLocalMap {static class Entry extends WeakReference

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