ThreadLocal的使用

╰+攻爆jí腚メ 2022-09-25 03:28 226阅读 0赞

ThreadLocal线程副本，可以理解为一种线程变量，作用域为当前线程，数据存放在ThreadLocal可以一个线程内共享。好处是避免了层与层之间的参数传递，实现松耦合。

public class SessionContainer {
    	private static final ThreadLocal<SessionCache> sessionThreadLocal = new ThreadLocal<SessionCache>();
    	public static SessionCache getSession() {
    		return sessionThreadLocal.get();
    	}
    	public static void setSession(SessionCache sessionCache) {
    		sessionThreadLocal.set(sessionCache);
    	}
    	public static void clear() {
    		sessionThreadLocal.set(null);
    	}
    }

public class Global {
    	public static final ThreadLocal transferThreadLocal = new ThreadLocal();
    	public static Map<String, Object> getTransfer() {
    		Map<String, Object> map = (Map<String, Object>) transferThreadLocal.get();
    		if (map == null) {
    			map = new HashMap<String, Object>();
    			transferThreadLocal.set(map);
    		}
    		return map;
    	}
    
    	public static void setTransfer(String key, Object value) {
    		Map<String, Object> map = getTransfer();
    		map.put(key, value);
    		transferThreadLocal.set(map);
    	}
    }
    public class Test{
        public static void main(String[] args){
            Map<String, Object> transferMap = Global.getTransfer();
            transferMap.put("host", Global.getValue("weburl"));
            transferMap.put("webname", Global.getValue("webname"));
    
            Global.setTransfer("user", user);
        }
    }

首先，ThreadLocal 不是用来解决多线程资源访问的，通过ThreadLocal.set() 到线程中的对象是该线程自己使用的对象，其他线程是访问不到的。各个线程中访问的是不同的对象。 以下测试返回结果：

t2 com.sunyard.util.ThreadLocal2$Person@152236d9
    t1 null

public class ThreadLocal2 {
    	static ThreadLocal<Person> tl = new ThreadLocal<>();
    	public static void main(String[] args) {
    		new Thread(()->{
    			try {
    				TimeUnit.SECONDS.sleep(2);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    			System.out.println(Thread.currentThread().getName()+" "+tl.get());
    		},"t1").start();
    		
    		new Thread(()->{
    			try {
    				TimeUnit.SECONDS.sleep(1);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    			tl.set(new Person());
    			System.out.println(Thread.currentThread().getName()+" "+tl.get());
    		},"t2").start(); 
    	}
    	static class Person {
    		String name = "zhangsan";
    	}
    }