我們來(lái)看一下JavaWeb多線程ThreadLocal的簡(jiǎn)單使用，首先ThreadLocal肯定是全局共享的：

public class Tools
{
    public static ThreadLocal<String> t1 = new ThreadLocal<String>();
}

寫一個(gè)線程往ThreadLocal里面塞值：

public class ThreadLocalThread extends Thread
{
    private static AtomicInteger ai = new AtomicInteger();    
    public ThreadLocalThread(String name)
    {
        super(name);
    }    
    public void run()
    {
        try
        {
            for (int i = 0; i < 3; i++)
            {
                Tools.t1.set(ai.addAndGet(1) + "");
                System.out.println(this.getName() + " get value--->" + Tools.t1.get());
                Thread.sleep(200);
            }
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }
}

寫個(gè)main函數(shù)，啟動(dòng)三個(gè)ThreadLocalThread：

public static void main(String[] args) throws Exception
    {
        ThreadLocalThread a = new ThreadLocalThread("ThreadA");
        ThreadLocalThread b = new ThreadLocalThread("ThreadB");
        ThreadLocalThread c = new ThreadLocalThread("ThreadC");
        a.start();
        b.start();
        c.start();
    }

看一下運(yùn)行結(jié)果：

ThreadA get value--->1
ThreadC get value--->2
ThreadB get value--->3
ThreadB get value--->4
ThreadC get value--->6
ThreadA get value--->5
ThreadC get value--->8
ThreadA get value--->7
ThreadB get value--->9

看到每個(gè)線程的里都有自己的String，并且互不影響----因?yàn)榻^對(duì)不可能出現(xiàn)數(shù)字重復(fù)的情況。用一個(gè)ThreadLocal也可以多次set一個(gè)數(shù)據(jù)，set僅僅表示的是線程的ThreadLocal.ThreadLocalMap中table的某一位置的value被覆蓋成你最新設(shè)置的那個(gè)數(shù)據(jù)而已，對(duì)于同一個(gè)ThreadLocal對(duì)象而言，set后，table中絕不會(huì)多出一個(gè)數(shù)據(jù),這里要注意，如果第一次沒有給ThreadLocal設(shè)置值的話，是會(huì)返回null的。