Adapters allows client to make use of libraries and subsets without changing any code. As a consequence, Decorator supports recursive composition, which isn't possible with pure Adapters.Ģ. Facade makes an interface simpler.ĭecorator is thus more transparent to the application than an adapter is. Adapter converts one interface to another, Decorator doesn't alter interface but adds responsibility. Comparing Adapter Pattern with other Patterns:ġ. Struts also implement the following J2EE design patterns.Ħ. The process() method of the RequestProcessor uses the template method design pattern. Struts controller uses the command design pattern and the action classes use the adapter design pattern. What design patterns are used in Struts?Īns:Struts is based on model 2 MVC (Model-View-Controller) architecture. Essentially, the DAO acts as an adapter between the component and the data source.ĥ. Because the interface exposed by the DAO to clients does not change when the underlying data source implementation changes, this pattern allows the DAO to adapt to different storage schemes without affecting its clients or business components. The DAO completely hides the data source implementation details from its clients. The business component that relies on the DAO uses the simpler interface exposed by the DAO for its clients. The data source could be a persistent store like an RDBMS, an external service like a B2B exchange, a repository like an LDAP database, or a business service accessed via CORBA Internet Inter-ORB Protocol (IIOP) or low-level sockets. The DAO implements the access mechanism required to work with the data source. The DAO pattern allows data access mechanisms to change independently of the code that uses the data. The best solution is then to wrap all the calls inside a Session Bean, so the clients will have a single point to access (that is the session bean) that will take care of handling all the rest.Īns:The Data Access Object (or DAO) pattern: separates a data resource's client interface from its data access mechanisms adapts a specific data resource's access API to a generic client interface In other words, the risk is to have a solution that has a high network overhead, high coupling, poor reusability and mantainability. Multiple fine-grained invocations of Entity (or even Session) Beans add the overhead of network calls, even multiple transaction. The entire transfer has to be done in a single transaction otherwise is something goes south, the situation has to be restored.Īs you can see, multiple server-side objects need to be accessed and possibly modified. In this type of scenario, the client has to check that the user is authorized, get the status of the two accounts, check that there are enough money on the first one, and then call the transfer. Think of a bank situation, where you have someone that would like to transfer money from one account to another. It then provides a single interface for the functionality of an application or part of it, and it decouples lower level components simplifying the design. It is implemented as a higher level component (i.e.: Session EJB), and it contains all the iteractions between low level components (i.e.: Entity EJB). To improve application performance, Service Locator caches service objects to eliminate unnecessary JNDI (Java Naming and Directory Interface) activity that occurs in a lookup operation.Īns: Session facade is one design pattern that is often used while developing enterprise applications. The Service Locator hides the lookup process's implementation details and complexity from clients. Ans:The Service Locator pattern locates J2EE (Java 2 Platform, Enterprise Edition) services for clients and thus abstracts the complexity of network operation and J2EE service lookup as EJB (Enterprise JavaBean) Interview Questions - Home and JMS (Java Message Service) component factories.
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