ThreadLocal

ThreadLocal使用線程私有方式解決變量共享問題,主要運用在全局設置.

簡單事例代碼(來自java特種兵)

package com.ydy.thread.treadlocal;
/**
 * 
 * @author ydy
 * */
public class TreadLocalTest {

	static class ResourceClass{
		public final static ThreadLocal<String> RESOURCE_1=new ThreadLocal<>();
		public final static ThreadLocal<String> RESOURCE_2=new ThreadLocal<>();
	}
	static class A{
		public void setOne(String value) {
			ResourceClass.RESOURCE_1.set(value);
		}
		public void setTwo(String value) {
			ResourceClass.RESOURCE_2.set(value);
		}
	}
	
	static class B{
		public void display() {
			System.out.println(ResourceClass.RESOURCE_1.get()+":"+ResourceClass.RESOURCE_2.get());			
		}
	}
	
	public static void main(String[] args) {
		final A a=new A();
		final B b=new B();
		for(int i=0;i<15;i++) {
			final String resource1="線程-"+i;
			final String resource2=i+"";
			new Thread(new Runnable() {
				
				@Override
				public void run() {
					// TODO Auto-generated method stub
					try {
						a.setOne(resource1);
						a.setTwo(resource2);
						b.display();
					} catch (Exception e) {
						// TODO: handle exception
						e.printStackTrace();
					}finally {
						ResourceClass.RESOURCE_1.remove();
						ResourceClass.RESOURCE_2.remove();
					}
					
					
				}
			}).start();
		}
	}
}

實現原理

public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }

 void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
    }