已知在等比数列\(\{a _{n} \}\)中，\(a _{n} > 0\)，\(a _{1} =4\)，\( \dfrac {1}{a_{2}} - \dfrac {1}{a_{3}} = \dfrac {2}{a_{4}}\)．
\((1)\)求数列\(\{a _{n} \}\)的通项公式；
\((2)\)若\(b _{n} = \dfrac {1}{\log _{2}a_{n}\cdot \log _{2}a_{n+1}}\)，求数列\(\{b _{n} \}\)前\(n\)项的和．