clearbasketcontroller.java

卡耐基梅隆大学数据库教程SSD7

/**
 * Class <b>ClearBasketController</b> contains
 * the specification of a servlet that
 * clears all books to a library user's basket.
 *
 * @author CTE
 * @version 1.0
 */

import library.*;
import java.util.*;
import java.io.*;
import java.text.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class ClearBasketController extends HttpServlet
{

    /**
     * Init method called once by the servlet container
     * @param conf ServletConfig servlet configuration object supplied by servlet container
     * @return void
     */
    public void init(ServletConfig conf) throws ServletException
    {
	super.init(conf);
    }

    /**
     * method doGet()
     * All GET and POST forms are handled by the same function, so process
     * GET requests to the doPost method.
     * @param request HttpServletRequest request object
     * @param response HttpServletResponse response object
     * @return void
     */
    public void doGet( HttpServletRequest request, HttpServletResponse response )
    {
	doPost( request, response );
    }
    
    /**
     * method doPost()
     * Process all HTML forms using the doPost method.  This clears 
     * the session scoped JavaBean LibraryBasket.
     * @param request HttpServletRequest request object
     * @param response HttpServletResponse response object
     * @return void
     */
    public void doPost( HttpServletRequest request, HttpServletResponse response )
    {
	// Get the current http session from the request object.
	HttpSession mySession = request.getSession();

	// Get the session scoped bean named basket from the session.
	library.LibraryBasket Basket = (library.LibraryBasket) mySession.getAttribute( "Basket" );

	// Get the number of books in the basket.
	int numbooks = Basket.getnumBooks();
	String [] ISBNS = new String[numbooks];

	// Get the isbns of the books in the basket.
	ISBNS=Basket.getBooks();
	for( int i=0; i<numbooks; i++ )
	    {
		// Get the quantity of this book.
		int quantity = Basket.getQuantity( ISBNS[i] );
		// Loop on the quantity and remove the book.
		for( int j=0; j<quantity; j++ )
		    Basket.removeItem( ISBNS[i] );
	    }
	
	// Be sure to place the bean back into the session.
	mySession.setAttribute( "Basket", Basket );
	try
	    {
		response.sendRedirect( "/library/showbooks.jsp" );
	    }
	catch( Exception e )
	    {
		request.setAttribute( "errorstring", e.toString() );	
		try
		    {
			getServletConfig().getServletContext().getRequestDispatcher("/library/error.jsp").forward(request, response);
		    }
		catch(Exception e2)
		    {
			// Must display this error message on the console.
			System.err.println(e2.toString()); 
		    }
	    }
    }
    
}