Java线程中的线程本地变量ThreadLocal详解

/**
 * 数据库连接管理类
 * @author 爽
 *
 */
public class ConnectionManager {
 
	/** 线程内共享Connection，ThreadLocal通常是全局的，支持泛型 */
	private static ThreadLocal<Connection> threadLocal = new ThreadLocal<Connection>();
	
	public static Connection getCurrConnection() {
		// 获取当前线程内共享的Connection
		Connection conn = threadLocal.get();
		try {
			// 判断连接是否可用
			if(conn == null || conn.isClosed()) {
				// 创建新的Connection赋值给conn(略)
				// 保存Connection
				threadLocal.set(conn);
			}
		} catch (SQLException e) {
			// 异常处理
		}
		return conn;
	}
	
	/**
	 * 关闭当前数据库连接
	 */
	public static void close() {
		// 获取当前线程内共享的Connection
		Connection conn = threadLocal.get();
		try {
			// 判断是否已经关闭
			if(conn != null && !conn.isClosed()) {
				// 关闭资源
				conn.close();
				// 移除Connection
				threadLocal.remove();
				conn = null;
			}
		} catch (SQLException e) {
			// 异常处理
		}
	}
}

protected T initialValue()

public T get()

public void set(T value)

public void remove()

/**
 * Sets the current thread's copy of this thread-local variable
 * to the specified value.  Most subclasses will have no need to
 * override this method, relying solely on the {@link #initialValue}
 * method to set the values of thread-locals.
 *
 * @param value the value to be stored in the current thread's copy of
 *        this thread-local.
 */
public void set(T value) {
	// 获取当前线程对象
	Thread t = Thread.currentThread();
	// 获取当前线程本地变量Map
	ThreadLocalMap map = getMap(t);
	// map不为空
	if (map != null)
		// 存值
		map.set(this, value);
	else
		// 创建一个当前线程本地变量Map
		createMap(t, value);
}
 
/**
 * Get the map associated with a ThreadLocal. Overridden in
 * InheritableThreadLocal.
 *
 * @param  t the current thread
 * @return the map
 */
ThreadLocalMap getMap(Thread t) {
	// 获取当前线程的本地变量Map
	return t.threadLocals;
}

/**
 * Returns the value in the current thread's copy of this
 * thread-local variable.  If the variable has no value for the
 * current thread, it is first initialized to the value returned
 * by an invocation of the {@link #initialValue} method.
 *
 * @return the current thread's value of this thread-local
 */
public T get() {
	Thread t = Thread.currentThread();
	ThreadLocalMap map = getMap(t);
	if (map != null) {
		ThreadLocalMap.Entry e = map.getEntry(this);
		if (e != null)
			return (T)e.value;
	}
	// 如果值为空，则返回初始值
	return setInitialValue();
}