ThreadLocal字面意思本地线程,ThreadLocal使每个线程之间是隔离的，数据是独立的，我们使用过session都知道 session是一个会话，我们可以用它来存储一些用户的基本信息，这样每个用户在服务端都能取到，ThreadLocal也可以做到， ThreadLocal将相应的信息存储在当前的线程中，只有当前线程能够访问，其他线程不能访问，其实ThreadLocal 可以说是一个定制化的Map。
下面我们通过一个示例来演示怎么使用ThreadLocal,我们用ThreadLocal来存储用户对象，然后取出用户对象，移除 用户对象 threadLocal.set(threadLocalUser)存储用户的信息 threadLocal.get()获取当前线程存储的信息 threadLocal.remove()移除当前线程储存的信息
如果我们在executorService.shutdown()关闭线程池后再去get()，那么将会返回null，因为线程池已经关闭 不知道是从那个线程中取，所以返回null。
package thread; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * ThreadLocal */ public class ThreadLocalTest { private static ThreadLocal<ThreadLocalUser> threadLocal = new ThreadLocal<ThreadLocalUser>(); final static ExecutorService executorService = Executors.newCachedThreadPool(); /** * 获取本地线程值 */ static void getThreadLocalUser(){ System.out.println(Thread.currentThread().getName()+" : "+threadLocal.get()); } /** * 移除本地线程值 */ static void removeThreadLocalUser(){ threadLocal.remove(); System.out.println(Thread.currentThread().getName()+" : "+threadLocal.get()); } public static void main(String[] args) { executorService.submit(() ->{ ThreadLocalUser threadLocalUser = new ThreadLocalUser(); threadLocalUser.setUserId("123456"); threadLocalUser.setRoleId("1"); threadLocal.set(threadLocalUser); getThreadLocalUser(); removeThreadLocalUser(); }); executorService.submit(() ->{ ThreadLocalUser threadLocalUser = new ThreadLocalUser(); threadLocalUser.setUserId("131420"); threadLocalUser.setRoleId("2"); threadLocal.set(threadLocalUser); getThreadLocalUser(); removeThreadLocalUser(); }); executorService.shutdown(); } }
我们可以看出,ThreadLocal其实是存放在threadLocals，而threadLocals是ThreadLocalMap 的一个成员变量，所以ThreadLocal实际上只是一个外壳，里面层层封装
public void set(T value) { Thread t = Thread.currentThread(); ThreadLocalMap map = getMap(t); if (map != null) map.set(this, value); else createMap(t, value); } ThreadLocal.ThreadLocalMap threadLocals = null; ThreadLocalMap getMap(Thread t) { return t.threadLocals; }
