java ThreadLocal

import java.io.*;
import java.util.logging.*;
public class SimpleThreadLogger {
	private static final java.lang.ThreadLocal<Logger> threadLocal = new java.lang.ThreadLocal<Logger>();

	// 输出信息
	public static void log(String msg) {
		getThreadLogger().log(Level.INFO, msg);
	}

	// 根据线程获得专属Logger
	private static Logger getThreadLogger() {
		Logger logger = threadLocal.get();
		if (logger == null) {
			try {
				logger = Logger.getLogger(Thread.currentThread().getName());
				// Logger 默认是在主控台输出
				// 我们加入一个文件输出的Handler
				// 它会输出XML的记录文件
				logger.addHandler(new FileHandler(Thread.currentThread().getName() + ".log"));
			} catch (IOException e) {
			}
			threadLocal.set(logger);
		}
		return logger;
	}
}
public class LoggerTest {
	public static void main(String[] args) {
		new TestThread("thread1").start();
		new TestThread("thread2").start();
		new TestThread("thread3").start();
	}
}

class TestThread extends Thread {
	public TestThread(String name) {
		super(name);
	}

	public void run() {
		for (int i = 0; i < 10; i++) {
			SimpleThreadLogger.log(getName() + ": message " + i);
			try {
				Thread.sleep(1000);
			} catch (Exception e) {
				SimpleThreadLogger.log(e.toString());
			}
		}
	}
}
import java.util.*;
public class ThreadLocal<T> {
	// 获得一个同步化的Map对象
	private Map<Thread, T> storage = Collections
			.synchronizedMap(new HashMap<Thread, T>());
	public T get() {
		// 获得目前执行get()方法的线程
		Thread current = Thread.currentThread();
		// 根据线程获得线程自有的资源
		T t = storage.get(current);
		// 如果还没有线程专用的资源空间
		// 则建立一个新的空间
		if (t == null && !storage.containsKey(current)) {
			t = initialValue();
			storage.put(current, t);
		}
		return t;
	}
	public void set(T t) {
		storage.put(Thread.currentThread(), t);
	}
	public T initialValue() {
		return null;
	}
}

注：使用ThreadLocal，一般都是声明在静态变量中，如果不断的创建ThreadLocal而且没有调用其remove方法，将会导致内存泄露。