java - NPE 在尝试在 Java 中创建多个记录器时使用静态 ThreadLocal 记录器

Question

我正在尝试使用 Threadlocal 创建多个静态记录器，以便每个静态 threadlocal 将记录到具有不同消息的单独文件。下面是我的示例代码:

public class LoggerTest implements Runnable
{
    private static ThreadLocal<Logger> log=new ThreadLocal<Logger>();
    FileHandler fh;
    String str;
    public LoggerTest(int counter,String instanceName) throws SecurityException, IOException
    {
        str=instanceName;
        log.set(Logger.getLogger("Logging"+counter));
        log.get().info("m");
        fh=new FileHandler(instanceName+".log");
        fh.setFormatter(new SimpleFormatter());
        log.get().addHandler(fh);
    }
    public static void main(String[] args) throws SecurityException, IOException
    {
        Thread t1=new Thread(new LoggerTest(1, "file"+1),"Thread1");
        Thread t2=new Thread(new LoggerTest(2, "file"+2),"Thread2");
        Thread t3=new Thread(new LoggerTest(3, "file"+3),"Thread3");
        t1.start();t2.start();t3.start();
    }

    @Override
    public void run()
    {
        for (int i = 0; i < 10; i++)
        {
            log.get().info("Message"+i);
            try
            {
                Thread.sleep(5000);
            } catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}

根据 this每个线程都有自己的静态 ThreadLocal 变量。所以我创建了 3 个线程来使用 ThreadLocal 登录不同的文件。有人能指出我在理解静态 ThreadLocal 的概念时哪里出错了吗

我的目标:使用静态 ThreadLocal 实现多个记录器TIA!!!

Answer 1

这是因为您需要重写ThreadLocal 类的initialValue() 方法。例如。

/** Thread local logger. */
private static final ThreadLocal<Logger> LOGGER = new ThreadLocal<Logger> () {

    @Override
    protected Logger initialValue() {
        return LoggerFactory.getLogger(ThisClass.class);
    }
};