What is ThreadLocal ?

ThreadLocal allows to associate a per-thread value with an object.

It provides get / set methods that maintains a separate copy of the value for each thread that uses it.

Example

private static ThreadLocal<Connection> threadLocal = new ThreadLocal<Connection>() {

   public Connection initialValue() {

       return DriverManager.getConnection(URL);

   }

};

public static Connection getConnection() {

   return threadLocal.get();

}

When a thread calls ThreadLocal.get for the first time, initialValue method provides the initial value.

Thread specific values are stored in the Thread object itself and garbage collected when thread terminates.