ThreadLocal学习理解

ThreadLocal作用：
1.与当前线程绑定，存储当前线程的变量副本，只要是该线程未结束，都可以通过get方法获取到变量；各线程有互相隔离；
2.可以达到线程安全的效果，避免同步带来的性能消耗。

简单的小例子：

/**
 *
 * ThreadLocal使用案例一
 *    模拟线程数据隔离
 * @author Kevin
 */
public class ThreadLocalDemo1 {

    private static ThreadLocal<Integer> threadLocal = new ThreadLocal<>();

    public static void main(String[] args) {

        Thread t1 = new Thread(new MyRequest(true));
        t1.start();
        Thread t2 = new Thread(new MyRequest(true));
        t2.start();

        Thread t3 = new Thread(new MyRequest(false));
        t3.start();


    }

    static class MyRequest implements Runnable {

        private boolean setThreadLocal;

        MyRequest(boolean setThreadLocal){
            this.setThreadLocal = setThreadLocal;
        }
        @Override
        public void run(){
            try {
                for(int i=0;i<5;i++){
                    if(setThreadLocal) {
                        threadLocal.set(i);
                    }
                    System.out.println("this current thread name is :" + Thread.currentThread().getName() + "[" +  threadLocal.get() + "]");
                }
            }finally {
                /**
                 * 这里把ThreadLocal定义为static还有一个好处就是，由于ThreadLocal有强引用在，
                 * 那么在ThreadLocalMap里对应的Entry的键会永远存在，那么执行remove的时候就可以正确进行定位到并且删除！！！
                 */
                threadLocal.remove();
            }
        }
    }
}

结果：

D:Javajdk1.8.0_131injava.exe "-javaagent:D:JetBrainsIntelliJ IDEA Community Edition 2019.1.1libidea_rt.jar=53791:D:JetBrainsIntelliJ IDEA Community Edition 2019.1.1in" -Dfile.encoding=UTF-8 -classpath D:Javajdk1.8.0_131jrelibcharsets.jar;D:Javajdk1.8.0_131jrelibdeploy.jar;D:Javajdk1.8.0_131jrelibextaccess-bridge-64.jar;D:Javajdk1.8.0_131jrelibextcldrdata.jar;D:Javajdk1.8.0_131jrelibextdnsns.jar;D:Javajdk1.8.0_131jrelibextjaccess.jar;D:Javajdk1.8.0_131jrelibextjfxrt.jar;D:Javajdk1.8.0_131jrelibextlocaledata.jar;D:Javajdk1.8.0_131jrelibext
ashorn.jar;D:Javajdk1.8.0_131jrelibextsunec.jar;D:Javajdk1.8.0_131jrelibextsunjce_provider.jar;D:Javajdk1.8.0_131jrelibextsunmscapi.jar;D:Javajdk1.8.0_131jrelibextsunpkcs11.jar;D:Javajdk1.8.0_131jrelibextzipfs.jar;D:Javajdk1.8.0_131jrelibjavaws.jar;D:Javajdk1.8.0_131jrelibjce.jar;D:Javajdk1.8.0_131jrelibjfr.jar;D:Javajdk1.8.0_131jrelibjfxswt.jar;D:Javajdk1.8.0_131jrelibjsse.jar;D:Javajdk1.8.0_131jrelibmanagement-agent.jar;D:Javajdk1.8.0_131jrelibplugin.jar;D:Javajdk1.8.0_131jrelib
esources.jar;D:Javajdk1.8.0_131jrelib
t.jar;D:idea_workspacejuly-projectjava-base	argetclasses;D:
epositoryorgprojectlomboklombok1.18.8lombok-1.18.8.jar;D:
epositoryjunitjunit4.12junit-4.12.jar;D:
epositoryorghamcresthamcrest-core1.3hamcrest-core-1.3.jar com.base.thread.ThreadLocalDemo1
this current thread name is :Thread-1[0]
this current thread name is :Thread-2[null]
this current thread name is :Thread-2[null]
this current thread name is :Thread-2[null]
this current thread name is :Thread-2[null]
this current thread name is :Thread-0[0]
this current thread name is :Thread-2[null]
this current thread name is :Thread-1[1]
this current thread name is :Thread-0[1]
this current thread name is :Thread-0[2]
this current thread name is :Thread-1[2]
this current thread name is :Thread-0[3]
this current thread name is :Thread-0[4]
this current thread name is :Thread-1[3]
this current thread name is :Thread-1[4]

Process finished with exit code 0

待补充完善：

• 线程池下的ThreadLocal使用思考，remove的重要性
• 深层剖析Thread ThreadLocalMap ThreadLocal关系
• ThreadLocal get和set方法
• 应用案例分析

参考：
Java ThreadLocal的使用
手撕面试题threadlocal
threadlocal使用