Web services are usually encapsulated or implemented by components in the backend or legacy systems. Since many legacy systems are data-centric or data-intensive, their components have more or less data dependencies between each other. If such explicit or implicit data dependencies were ignored or not dealt with carefully, they would cause unexpected behaviors and even errors of web services. In this paper, we propose a middleware-based approach to the detection and solution of interferences between web services caused by data dependencies between backend components. With a demonstration on J2EE (Java 2 Platform Enterprise Edition), this paper makes three contributions: Firstly, it investigates such an interference problem neglected by current research and practice with a real case of J2EE-enabled web services. Secondly, it enhances a J2EE application server to automatically detect interferences between web services caused by data dependencies among Enterprise JavaBeans. Thirdly, it proposes four solution patterns of the interferences, which are successfully applied to a real case.