jsp基于Web的可维护的数据库浏览器(源代码)

package ui; import java.io.Serializable; import javax.swing.*; import javax.servlet.http.*; import javax.servlet.jsp.*; // Import the NamveValue model import jspstyle.*; import java.util.HashMap; /** * Class to provide page flow logic for the Data Source Explorer. * All requests go to this class. This class is responsible for * instantiating the beans required by the system. * This class uses reflection to instantiate request handlers as * required. */ public class RequestController implements Serializable { //--------------------------------------------------------------------- // Class data and methods //--------------------------------------------------------------------- /** * URL of the system's login page. * We'll redirect users to this if they don't have a connection */ public static final String LOGIN_PAGE = "login.html"; /** Package from which to attempt to load RequestHandler objects */ private static final String REQUEST_HANDLER_PACKAGE = "ui.requesthandlers"; /** * Name of the session bean that will be used for this application. * This must be matched by the useBean actions in the JSPs. */ private static final String SESSION_BEAN_NAME = "browseSession"; /** * Convenience method for RequestHandler implementations, allowing Java classes to access * the session bean easily. Unlike checkSessionBeanIsAvailable(), this method will * throw an exception if the bean has not already been instantiated. * @return the session bean, which must have been instantiated already. */ public static BrowseSession FindSessionBean(PageContext pageContext, RequestHandler rh) throws BrowseException { BrowseSession session = (BrowseSession) pageContext.getAttribute(RequestController.SESSION_BEAN_NAME, PageContext.SESSION_SCOPE); if (session == null) throw new BrowseException("Internal error: illegal state. Session bean shouldn't be null handling action " + rh.getClass()); return session; } //--------------------------------------------------------------------- // Instance data //--------------------------------------------------------------------- /** * Hash table of RequestHandler instances, keyed by class name. * This is used for performance optimization, to avoid the need * to load a class by name to process each request. */ private HashMap handlerHash = new HashMap(); //--------------------------------------------------------------------- // Public methods //--------------------------------------------------------------------- /** * This is the key method through which all request to the * application are sent. * Process a request, updating the session and * returning the URL of the resulting JSP view */ public String getNextPage(PageContext pageContext, HttpServletRequest request) throws BrowseException { String action = request.getParameter("action"); // If no action was specified, the user must first log in if (action == null || action.equals("")) return LOGIN_PAGE; // If we have an action parameter, obtain the RequestHandler that implements // the action. This method will throw a BrowseException if no handler is // associated with the action. RequestHandler requestHandler = getHandlerInstance(action); // Create the session bean if it doesn't exist checkSessionBeanIsAvailable(pageContext); // Return the URL of the view the RequestHandler instance // chooses after doing the work of processing the request return requestHandler.handleRequest(pageContext, request); } // getNextPage /** * Locate and return the RequestHandler instance for this action. * Instances are stored in a hash table once instantiated, so after the initial * use of Class.forName() this method is very fast and does not rely on * reflection. */ private RequestHandler getHandlerInstance(String action) throws BrowseException { String handlerName = REQUEST_HANDLER_PACKAGE + "." + action; RequestHandler requestHandler = (RequestHandler) handlerHash.get(handlerName); if (requestHandler == null) { // We don't have a handler instance associated with this action, // so we need to instantiate one and put in in our hash table try { System.out.println("Loading handler instance..."); // Use reflection to load the class by name Class handlerClass = Class.forName(handlerName); // Check the class we obtained implements the RequestHandler interface if (!RequestHandler.class.isAssignableFrom(handlerClass)) throw new BrowseException("Class " + handlerName + " does not implement the RequestHandler interface " ); // Instantiate the request handler object requestHandler = (RequestHandler) handlerClass.newInstance(); // Save the instance so we don't have to load it dynamically to process // further requests from this user handlerHash.put(handlerName, requestHandler); } catch (ClassNotFoundException ex) { throw new BrowseException("No handler for action [" + handlerName + "]: class " + handlerName + " could not be loaded. " + ex); } catch (InstantiationException ex) { // It probably doesn't have a no-argument constructor throw new BrowseException("Class "+ handlerName + " could not be instantiated. " + " Is it a bean? " + ex); } catch (IllegalAccessException ex) { throw new BrowseException("Class " + handlerName + " could not be instantiated. " + "Does it have a public constructor? " + ex); } } // If we get to here, we have a valid RequestHandler instance, // whether it came from the hash table or from dynamical class loading return requestHandler; } // getHandlerInstance //--------------------------------------------------------------------- // Implementation methods //--------------------------------------------------------------------- /** * Return the user's session bean. Instantiate a new session bean and * put it in the session if none is found. */ private void checkSessionBeanIsAvailable(PageContext pageContext) { BrowseSession session = (BrowseSession) pageContext.getAttribute(SESSION_BEAN_NAME, PageContext.SESSION_SCOPE); if (session == null) { System.out.println("RequestController: creating session object"); session = new BrowseSession(); // Place the session in the PageContext, so it will be accessible // to JSPs as a session bean pageContext.setAttribute(SESSION_BEAN_NAME, session, PageContext.SESSION_SCOPE); } } } // class RequestController