Facade as the name suggests means the face of the building. The people walking past the road can only see this glass face of the building. They do not know anything about it, the wiring, the pipes and other complexities. The face hides all the complexities of the building and displays a friendly face.
Facade pattern hides the complexities of the system and provides an interface to the client from where the client can access the system. In Java, the interface JDBC can be called a facade. We as users or clients create connection using the “java.sql.Connection” interface, the implementation of which we are not concerned about. The implementation is left to the vendor of driver.
Let’s try and understand the facade pattern better using a simple example. Let’s consider a store. This store has a store keeper. In the storage, there are a lot of things stored e.g. packing material, raw material and finished goods.
You, as client want access to different goods. You do not know where the different materials are stored. You just have access to store keeper who knows his store well. Whatever you want, you tell the store keeper and he takes it out of store and hands it over to you on showing him the credentials. Here, the store keeper acts as the facade, as he hides the complexities of the system Store.
You, as client want access to different goods. You do not know where the different materials are stored. You just have access to store keeper who knows his store well. Whatever you want, you tell the store keeper and he takes it out of store and hands it over to you on showing him the credentials. Here, the store keeper acts as the facade, as he hides the complexities of the system Store.
Session Facade
Many business processes involve complex manipulations of business classes. Business classes often participate in multiple business processes or workflows. Complex processes that involve multiple business objects can lead to tight coupling between those classes, with a resulting decrease in flexibility and design clarity. Complex relationships between low-level business components make clients difficult to write.
The Session Facade pattern defines a higher-level business component that contains and centralizes complex interactions between lower-level business components. A Session Facade is implemented as a session enterprise bean. It provides clients with a single interface for the functionality of an application or application subset. It also decouples lower-level business components from one another, making designs more flexible and comprehensible.
Fine-grained access through remote interfaces is inadvisable because it increases network traffic and latency. The "before" diagram in Figure 1 below shows a sequence diagram of a client accessing fine-grained business objects through a remote interface. The multiple fine-grained calls create a great deal of network traffic, and performance suffers because of the high latency of the remote calls.
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Introducing a Session Facade, as shown in the "after" diagram in Figure 1, decreases network traffic and latency, because all access to fine-grained business objects is local. The Session Facade also acts as a Mediator between the business objects, decoupling their APIs from one another.
