4. In Rt $\triangle A B C$, $\angle C=90^{\circ}$, $C D$ is the altitude on the hypotenuse $A B$, and $C E$ is the angle bisector of $\angle C$. If $\frac{A E}{E B}=\frac{2}{3}$, then $\frac{A D}{D B}=$ $\qquad$ .
4. $\frac{4}{9}$