购物车操作

  近期刚完成二期的结业项目电子图书，其中主要训练的模块是购物车，后台发布前台显示，代码写的非常粗糙，JSP页面没有使用EL和JSTL，大片大片的<% %>。
  首先就其中购物车的增删改和清空购物车做一个笔记。
 

CartBean:
package  com.csthit.store.vo;

public   class  CartBean {
    
     private  Book book;  // 图书bean
     private   int  quantity;  // 设置图书数量
    
     public  Book getBook() {
         return  book;
    }
     public   void  setBook(Book book) {
         this .book  =  book;
    }
     public   int  getQuantity() {
         return  quantity;
    }
     public   void  setQuantity( int  quantity) {
         this .quantity  =  quantity;
    }
   
}

上面是对购物车的bean组件，下面放置几个对cart进行增删改清空的Servlet代码

String action  =  request.getParameter( " action " );   // 获得JSP页面的动作参数
        HttpSession session  =  request.getSession();  // 获取一个Session对象    
        String isbn  =  request.getParameter( " isbn " );  // 以图书的ISBN为条件查询图书
        
         /*
         * 添加一本书籍到购物车
          */
         if ( " add " .equals(action)) {
            String num  =  request.getParameter( " num " );   // JSP页面传递的数量参数，默认为1
             int  quantity  =  Integer.parseInt(num); 
            BookDAO bookdao  =   new  BookDAO(); 
            Book book  =  bookdao.queryByISBN(isbn);
            CartBean cb  =   null ;
            Map map  =   null ;
             if (session.getAttribute( " MYCART " ) != null ) {
                map  =  (HashMap)session.getAttribute( " MYCART " );
                 if (map.get(isbn) != null ) {
                    cb  =  (CartBean)map.get(isbn);
                    cb.setQuantity(cb.getQuantity() + quantity);
                }  else  {
                    cb  =   new  CartBean();
                    cb.setBook(book);
                    cb.setQuantity(quantity);
                }
                map.put(isbn, cb);
            }  else  {
                
                map  =   new  HashMap();
                cb  =   new  CartBean();
                cb.setBook(book);
                cb.setQuantity(quantity);
                map.put(isbn, cb);
                
            }
            
            session.setAttribute( " MYCART " , map);
            
            RequestDispatcher rd  =  request.getRequestDispatcher( " view_cart.jsp " );  
            rd.forward(request, response);
        
        }
        
         /*
         * 修改购物车数量
          */
         if ( " modify " .equals(action)) {
            String num  =  request.getParameter( " num " );
             int  quantity  =  Integer.parseInt(num);
            Map map  =  (Map)session.getAttribute( " MYCART " );
            CartBean cb  =   null ;
             if (quantity == 0 ) {   // 客户端如果把数量修改为0则删除当前书籍
                map.remove(isbn);
            }  else  {
                
                cb  =  (CartBean)map.get(isbn);
                cb.setQuantity(quantity);
                map.put(isbn, cb);
            }
            
            
            session.setAttribute( " MYCART " , map);
            
            RequestDispatcher rd  =  request.getRequestDispatcher( " view_cart.jsp " );
            rd.forward(request, response);
            
        }
        
         /*
         * 删除商品
          */
         if ( " delete " .equals(action)) {
            Map map  =  (Map)session.getAttribute( " MYCART " );
            map.remove(isbn);
            session.setAttribute( " MYCART " , map);
            RequestDispatcher rd  =  request.getRequestDispatcher( " view_cart.jsp " );
            rd.forward(request, response);
        }
        
         /*
         * 清空购物车，使Map的key长度为0
          */
         if ( " remove " .equals(action)) {
            
            Map map  =  (HashMap)session.getAttribute( " MYCART " );
            Object[] keys  =  map.keySet().toArray();
             for  ( int  i  =   0 ; i  <  keys.length; i ++ ) {
                map.remove((String)keys[i]);
            }
            
            session.setAttribute( " MYCART " , map);
            RequestDispatcher rd  =  request.getRequestDispatcher( " view_cart.jsp " );
            rd.forward(request, response);
        }