ThreadLocal使用详解

package com.dwz.concurrency.chapter33;

public class ThreadLocalSimpleTest {
    private static ThreadLocal<String> threadlocal = new ThreadLocal<String>() {
        @Override
        protected String initialValue() {
            return "dandan";
        };
    };
    
    public static void main(String[] args) throws InterruptedException {
        threadlocal.set("Alex");
        Thread.sleep(1000);
        System.out.println(threadlocal.get());
    }
}

package com.dwz.concurrency.chapter33;

import java.util.Random;

public class ThreadLocalComplexTest {
    private final static ThreadLocal<String> threadlocal = new ThreadLocal<>();
    
    private final static Random random = new Random(System.currentTimeMillis());
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(()->{
            threadlocal.set("T1");
            try {
                Thread.sleep(random.nextInt(1000));
                System.out.println(Thread.currentThread().getName() + "&&" + threadlocal.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        
        Thread t2 = new Thread(()->{
            threadlocal.set("T2");
            try {
                Thread.sleep(random.nextInt(1000));
                System.out.println(Thread.currentThread().getName() + "&&" + threadlocal.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("==========================");
        System.out.println(Thread.currentThread().getName() + "&&" + threadlocal.get());
    }
}

package com.dwz.concurrency.chapter33;

import java.util.HashMap;
import java.util.Map;
/**
 * The Thread-Specific Storage 模拟线程保险箱
 * 始终以当前线程作为key值
 * @param <T>
 */
public class ThreadLocalSimulator<T> {
    private final Map<Thread, T> storage = new HashMap<>();
    
    public void set(T t) {
        synchronized (this) {
            Thread key = Thread.currentThread();
            storage.put(key, t);
        }
    }
    
    public T get() {
        synchronized (this) {
            Thread key = Thread.currentThread();
            T value = storage.get(key);
            if(null == value) {
                return initialValue();
            }
            return value;
        }
    }

    public T initialValue() {
        return null;
    }
}

package com.dwz.concurrency.chapter33;

import java.util.Random;

public class ThreadLocalSimulatorTest {
    private final static ThreadLocalSimulator<String> threadlocal = new ThreadLocalSimulator<String>() {
        @Override
        public String initialValue() {
            return "No value";
        };
    };
    
    //seed
    private final static Random random = new Random(System.currentTimeMillis());
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(()->{
            threadlocal.set("T1");
            try {
                Thread.sleep(random.nextInt(1000));
                System.out.println(Thread.currentThread().getName() + "&&" + threadlocal.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        
        Thread t2 = new Thread(()->{
            threadlocal.set("T2");
            try {
                Thread.sleep(random.nextInt(1000));
                System.out.println(Thread.currentThread().getName() + "&&" + threadlocal.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("==========================");
        System.out.println(Thread.currentThread().getName() + "&&" + threadlocal.get());
    }
}