/**
 * 數(shù)據(jù)庫連接管理類
 * @author 爽
 *
 */
public class ConnectionManager {
 
	/** 線程內(nèi)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() {
		// 獲取當(dāng)前線程內(nèi)共享的Connection
		Connection conn = threadLocal.get();
		try {
			// 判斷連接是否可用
			if(conn == null || conn.isClosed()) {
				// 創(chuàng)建新的Connection賦值給conn(略)
				// 保存Connection
				threadLocal.set(conn);
			}
		} catch (SQLException e) {
			// 異常處理
		}
		return conn;
	}
	
	/**
	 * 關(guān)閉當(dāng)前數(shù)據(jù)庫連接
	 */
	public static void close() {
		// 獲取當(dāng)前線程內(nèi)共享的Connection
		Connection conn = threadLocal.get();
		try {
			// 判斷是否已經(jīng)關(guān)閉
			if(conn != null && !conn.isClosed()) {
				// 關(guān)閉資源
				conn.close();
				// 移除Connection
				threadLocal.remove();
				conn = null;
			}
		} catch (SQLException e) {
			// 異常處理
		}
	}
}

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) {
	// 獲取當(dāng)前線程對(duì)象
	Thread t = Thread.currentThread();
	// 獲取當(dāng)前線程本地變量Map
	ThreadLocalMap map = getMap(t);
	// map不為空
	if (map != null)
		// 存值
		map.set(this, value);
	else
		// 創(chuàng)建一個(gè)當(dāng)前線程本地變量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) {
	// 獲取當(dāng)前線程的本地變量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;
	}
	// 如果值為空，則返回初始值
	return setInitialValue();
}