线程本地变量ThreadLocal源码解读

  1 1/**
  2 * 数据库连接管理类
  3 * @author 爽
  4 *
  5 */
  6 6public class ConnectionManager {
  7 
  8    /** 线程内共享Connection，ThreadLocal通常是全局的，支持泛型 */
  9    private static ThreadLocal<Connection> threadLocal = new ThreadLocal<Connection>();
 10 
 11    public static Connection getCurrConnection() {
 12        // 获取当前线程内共享的Connection  
 13        Connection conn = threadLocal.get();
 14        try {
 15            // 判断连接是否可用  
 16            if(conn == null || conn.isClosed()) {
 17                // 创建新的Connection赋值给conn(略)  
 18                // 保存Connection  
 19                threadLocal.set(conn);
 20            }
 21        } catch (SQLException e) {
 22            // 异常处理  
 23        }
 24        return conn;
 25    }
 26 
 27    /**
 28     * 关闭当前数据库连接
 29     */
 30    public static void close() {
 31        // 获取当前线程内共享的Connection  
 32        Connection conn = threadLocal.get();
 33        try {
 34            // 判断是否已经关闭  
 35            if(conn != null && !conn.isClosed()) {
 36                // 关闭资源  
 37                conn.close();
 38                // 移除Connection  
 39                threadLocal.remove();
 40                conn = null;
 41            }
 42        } catch (SQLException e) {
 43            // 异常处理  
 44        }
 45    }
 46 }

  1 /**
  2  * Sets the current thread‘s copy of this thread-local variable
  3  * to the specified value.  Most subclasses will have no need to
  4  * override this method, relying solely on the {@link #initialValue}
  5  * method to set the values of thread-locals.
  6  *
  7  * @param value the value to be stored in the current thread‘s copy of
  8  *        this thread-local.
  9  */
 10 public void set(T value) {
 11     // 获取当前线程对象  
 12     Thread t = Thread.currentThread();
 13     // 获取当前线程本地变量Map  
 14     ThreadLocalMap map = getMap(t);
 15     // map不为空  
 16     if (map != null)
 17         // 存值  
 18         map.set(this, value);
 19     else
 20         // 创建一个当前线程本地变量Map  
 21         createMap(t, value);
 22 }
 23 
 24 /**
 25  * Get the map associated with a ThreadLocal. Overridden in
 26  * InheritableThreadLocal.
 27  *
 28  * @param  t the current thread
 29  * @return the map
 30  */
 31 ThreadLocalMap getMap(Thread t) {
 32     // 获取当前线程的本地变量Map  
 33     return t.threadLocals;
 34 }

  1 /**
  2  * Returns the value in the current thread‘s copy of this
  3  * thread-local variable.  If the variable has no value for the
  4  * current thread, it is first initialized to the value returned
  5  * by an invocation of the {@link #initialValue} method.
  6  *
  7  * @return the current thread‘s value of this thread-local
  8  */
  9 public T get() {
 10     Thread t = Thread.currentThread();
 11     ThreadLocalMap map = getMap(t);
 12     if (map != null) {
 13         ThreadLocalMap.Entry e = map.getEntry(this);
 14         if (e != null)
 15             return (T)e.value;
 16     }
 17     // 如果值为空，则返回初始值  
 18     return setInitialValue();
 19 }