request.getRequestDispatch與response.sendRedirect區別

getRequestDispatcher是服務器內部跳轉，地址欄信息不變，只能跳轉到web應用內的網頁。 
sendRedirect是頁面重定向，地址欄信息改變，可以跳轉到任意網頁。 

//獲得所有的商品的類別數據
        AdminProductService service = new AdminProductService();
        List<Category> categoryList = null;
        try {
            categoryList = service.findAllCategory();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        
        request.setAttribute("categoryList", categoryList);
        
        request.getRequestDispatcher("/admin/product/add.jsp").forward(request, response);
        

AdminProductService service = new AdminProductService();
        try {
            service.addProduct(product);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        
        //跳轉到列表頁面
        response.sendRedirect(request.getContextPath()+"/adminProductList");