The Java object-oriented programming language has been the subject of an important involvement from programmers and the industry. Especially for applications related to the Web. The problem of such a rapid penetration of Java programs into commercial products is that software engineers do not have any methodology and have to develop complex parallel applications. Here, we present a formal development methodology based on the stepwise refinement of CO-OPN/2 formal specifications, using a real Web parallel application. Starting from a centralized view, we present the following refinement steps: data distribution, behavior distribution, communication layer, and Java program. During the whole refinement process, we study the evolution and the verification of one specific property.