In this paper, we present a case study of the power consumption and performance tradeoffs in Java application servers. We run SPECjEnterprise2010 on two platforms with different CPUs, namely, AMD Phenom II and Intel Atom. We investigate the performance and power consumption behaviors against the increasing system size and the relative performance between two CPUs. We also study the effectiveness of the dynamic frequency scaling (DFS) on Phenom and HyperThreading (HT) on Atom. Phenom achieves 8.5 times higher transaction throughput with 18.6 times more dynamic power consumption: Thus, the relative power consumption of Phenom against Atom is 218%. DFS parameter tuning reduces the dynamic power consumption of the Phenom-based server by up to 31%. However, it also has a side effect of higher transaction response time when the load level is fluctuated. HT improves the performance of the Atom server by up to 47% (standard workload) or 70% (individual transaction). HT does not reduce the power consumption of standard workload, but it works for individual transactions by up to 30% reduction of normalized power.