CHAPTER 11 REST-BASED MODEL VIEW CONTROLLER (Bulletproof web design) PATTERN
CHAPTER 11 REST-BASED MODEL VIEW CONTROLLER PATTERN Parent is the core of the entire system and is the bridge that binds all the pieces together. However, to keep it simple for Parent, Parent knows about only the inner circle of types. In the diagram, Google, Amazon, and HttpServlet know about the outer circle of types (SearchRequest, SearchResult) that are passed across the bridge. Implementing a Parent Implementing the Parent interface is a two-step process because the Parent interface plays the central role of processing the data. Let s consider the context. The Parent interface instance is responsible for executing the Command implementations, gathering the results, and making the request information available. Through all of these responsibilities, the Parent interface cannot use specific types but must use the general defined types. Additionally, the Parent interface implementation has to function whether the request is asynchronous or synchronous. The first step when implementing Parent is to define a base class that provides a certain amount of common functionality. The second step is then to create either an asynchronous or synchronous implementation. You need to separate an asynchronous implementation from a synchronous one because of how the results and threads are managed. Implementing the Base Class Before the synchronous and asynchronous Parent implementations are outlined, the first step is to outline the base type. The class ParentBase implements Parent, and a subset of the implemented functionality is outlined as follows (the remaining pieces will be explained in a moment): public abstract class ParentBase implements Parent { private List _commands = new LinkedList(); public void addCommand( Command cmd) { _commands.add( cmd); } public Iterator getCommands() { return _commands.iterator(); } public void clearAllCommands() { _commands.clear(); } The code excerpt shows that the individual local client instances (Command) are managed in a LinkedList. To add a local client, the method addCommand is used. To remove all local client instances, the method clearAllCommands is used. Because we are coding in a managed code environment, removing the Command instances does not equate to deleting them. They will be deleted when there are no references to the local client instances. This is important because when the local client instances are cleared, the threads referencing the local client instances will still be executing. It would be very inappropriate to have to wait until all of the old local client instances have finished executing, or to stop the execution in midstream. The remaining functionality implemented by ParentBase relates to executing the local clients through the Command interface. The execution of the local clients is on a per thread basis. Each local client is allocated a thread so that the individual executions can occur concurrently. Some readers may comment that spinning off an individual thread in a heavily multithreaded environment is inefficient. Granted, the statement is true, but consider the context, where the
If you are looking for affordable and reliable webhost to host and run your business application visit our ftp web hosting services.