  The BESIII Collaboration recently observed a new charmonium-like vector state
$Y(3872)$ in $e^+e^-\rightarrow D\bar{D}$, which should be the first P-wave
$D\bar{D}^*/\bar{D}D^*$ molecular resonance. The experimental and theoretical
identification of the P-wave dimeson state holds paramount importance in
enhancing our comprehension of the non-perturbative QCD and few-body physics.
Its existence is firmly established in a unified meson-exchange model which
simultaneously depicts the features of the $\chi_{c1}(3872)$, $Z_c(3900)$ and
$T_{cc}(3875)$. This scenario can be directly examined in the
$e^+e^-\rightarrow D\bar{D}^*/\bar{D}D^*$ cross section to see whether a
resonance exists at the threshold. The credibility of the investigations is
also ensured by the fact that the P-wave interaction dominantly arises from the
well-known long-range pion exchange. Additionally, the existence of the P-wave
resonance only depends on the interaction strength and is less sensitive to the
potential shapes. We extensively calculate all systems up to P-wave with
various quantum numbers and predict a dense population of the
$D\bar{D}^*/\bar{D}D^*$ and $DD^*$ states, where the S-wave
$D\bar{D}^*/\bar{D}D^*$ state with $I^G (J^{PC})=0^- (1^{+-})$, P-wave
$D\bar{D}^*/\bar{D}D^*$ state with $I^G(J^{PC})=0^+(0^{-+})$, and P-wave $DD^*$
state with $I(J^P)=0(0^-)$ are more likely to be observed in experiments.
