The emergence of the microservice-oriented architecture (MSA) has led to increased maintainability, better readability, and better scalability. All these advantages make migrating a monolithic software towards an MSA an attractive prospect for organizations. The migration process is recognized to be complex and consequently risky and costly. This process is composed of two phases: (1) the microservice-based architecture recovery phase and (2) the transformation (i.e. materialization) phase. In this paper, we propose a systematic approach to transform an object-oriented monolithic application towards an MS-oriented one by applying a set of transformation pattern. To validate our approach we automated it with our tool MonoToMicro, and applied it on a set of monolithic Java applications to be migrated towards microservices-based ones.