Servlet版购物车

最新推荐文章于 2022-04-27 00:08:58 发布

原创最新推荐文章于 2022-04-27 00:08:58 发布 · 1.1k 阅读

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1.通过Servlet来构造一个最简单的购物车，Servlet是JSP的基础，因此利用这个例子来看看Servlet的一些要点。因此，这里做一下限制，只能使用servlet和html。

html代码如下：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta http-equiv="Pragma" content="no cache">
<meta http-equiv="Cache-control" content="no cache">
<meta http-equiv="Expires" content="0">
<title>Shopping Cart using Servlet</title>
</head>
<body>
	<center>
		<h1>Simple SHOPPING CART</h1>
		
		<form method="post" action="SelectionServlet">
			<table>
				<tr>
					<td><input type="Radio" name="Product" value="apples" checked>Apples</td>
				</tr>
				<tr>
					<td><input type="Radio" name="Product" value="pears" checked>Pears</td>
				</tr>
				<tr>
					<td><input type="Radio" name="Product" value="Checkout" checked>Go to checkout</td>
				</tr>
			</table>
			<br />
			<input type="submit" value="submit" />
		
		</form>
	</center>
</body>
</html>

要点：

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta http-equiv="Pragma" content="no cache">
<meta http-equiv="Cache-control" content="no cache">
<meta http-equiv="Expires" content="0">

这部分用于控制禁止客户端缓存。

2.SelectionServlet如下

public class SelectionServlet extends HttpServlet {

	private final float APPLES_PRICE = 1.45F;
	private final float PEARS_PRICE = 1.75F;
	
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		String curProd = request.getParameter("Product");
		HttpSession cart = request.getSession();
		cart.setAttribute("currentProd", curProd);
		//cart.putValue("currentProd", curProd);
		if(curProd.equals("Checkout"))
			response.sendRedirect("CheckoutServlet");
		else
			sendPage(response,curProd);
	}
}

SelectionServlet用于判断用户选择。并将缓存放到session到中。使用的是session.setAttribute()方法。

如果用户行为为checkout，这直接重定向为 CheckoutServlet，否则执行sendPage方法。该方法用于输出一个供用户做进一步选择的界面。

根据MVC的设计原则，Servlet理应只作为控制器，但这里用起做结果输出，使代码显的非常的不可控。

	private void sendPage(HttpServletResponse response, String curProd) throws IOException {
		// TODO Auto-generated method stub
	    response.setContentType("text/html");
	    PrintWriter out = response.getWriter();
	    out.println("<html>");
	    out.println("<head>");
	    out.println("<title>" + curProd + "</title>");
	    out.println("</head>");
	    out.println("<body>");
	    out.println("<center>");
	    out.println("<h1>" + curProd + "</h1>");
	    out.println("<form method='post' action='WeightServlet'");
	    out.println("<table>");
	    out.println("<tr>");
	    out.println(" <td>Quantity required (kg)");
	    out.println(" <input type='Text' name='Qty'" + " value='' size=5></td>");
	    out.println("</tr>");
	    
	    out.println("<tr><td><input type='Radio'"
	        + " name='Option' value='Add' CHECKED>Add to cart.</td></tr>");
	    
	    out.println("<tr><td><input type='Radio'" + " name='Option' value='Remove'>");
	    out.println("Remove item from cart.</td></tr>");
	    
	    out.println("<tr><td><input type='Radio'" + " name='Option' value='Next'>");
	    out.println("Choose next item.</td></tr>");

	    out.println("<tr><td><input type='Radio'" + " name='Option' value='Checkout'>");
	    out.println("Go to checkout.</td></tr>");
	    out.println("</table>");

	    out.println("<input type='Submit' value='Submit'>");
	    out.println("</form>");
	    out.println("</center>");
	    out.println("</body>");
	    out.println("</html>");
	    out.flush();
	}

这里输出了一张表单，并且该表单的action指定的是 WeightServlet。

public class WeightServlet extends HttpServlet {

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		HttpSession cart = request.getSession();
		String curProd = (String) cart.getAttribute("currentProd");
		String choice = request.getParameter("Option");

		if (choice.equals("Next"))
			response.sendRedirect("ShoppingCart.html");
		if (choice.equals("Checkout"))
			response.sendRedirect("CheckoutServlet");
		if (choice.equals("Add")) {
			doAdd(cart, request);
			response.sendRedirect("ShoppingCart.html");
		}
		if (choice.equals("Remove"))
		{
			doRemove(cart);
			response.sendRedirect("ShoppingCart.html");
		}
	}
}

这里再次进行flow control，根据用户的选择做出不同的响应。更为关键的是，每次做出的选择我们都使用了session进行了跟踪，将其存储在服务器端，当用户再次选择时，不会丢失结果。

与设置session相似的是，得到session的值使用 session.getAttribute()方法。同样，删除session的方法时调用 session.removeAttribute()方法。

doRemove()和doAdd()方法如下：

	private void doRemove(HttpSession cart) {
		String currentProduct = (String) cart.getAttribute("currentProd");
	    Object product = cart.getAttribute(currentProduct);
	    if (product != null)
	      cart.removeAttribute(currentProduct);
	}

	private void doAdd(HttpSession cart, HttpServletRequest request) {
		String curProd = (String) cart.getAttribute("currentProd");
		String qty = request.getParameter("Qty");
		if(qty!=null){
			if(curProd.equals("apples"))
				cart.setAttribute("apples", qty);
			else 
				cart.setAttribute("pears", qty);
		}
	}

最后，我们关注最终转发的CheckoutServlet，其用于显示用户的购物列表。

public class CheckoutServlet extends HttpServlet {
	private final float APPLES_PRICE = 1.45F;
	private final float PEARS_PRICE = 1.75F;

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		HttpSession cart = request.getSession();
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		
		out.println("<html>");
		out.println("<head>");
		out.println("<title>Checkout</title>");
		out.println("</head>");
		out.println("<body>");
		out.println("<center>");
		out.println("<h1>Order List</h1>");
		out.println("<table BORDER=2>");
		out.println("<tr>");
		out.println("<th>Item</th>");
		out.println("<th>Weight(kg)</th>");
		out.println("<th>Costs</th>");
		out.println("</tr>");
		
		cart.removeAttribute("currentProd");
		Enumeration<?> prodNames = cart.getAttributeNames();
		float totalCost = 0;
		int numProducts = 0;
		while (prodNames.hasMoreElements()) {
			float wt = 0, cost = 0;
			String product = (String) prodNames.nextElement();
			String stringWt = (String) cart.getAttribute(product);
			wt = Float.parseFloat(stringWt);
			
			if (product.equals("apples"))
				cost = APPLES_PRICE * wt;
			else if (product.equals("pears"))
				cost = PEARS_PRICE * wt;
			
			out.println("<tr>");
			out.println("<td>" + product + "</td>");
			out.println("<td>" + wt + "</td>");
			out.println("<td>" + cost + "</td>");
			out.println("</tr>");
			totalCost += cost;

			numProducts++;
		}
		if (numProducts == 0) {
			out.println("<tr><td>*** No orders placed! ***</td></tr>");
		} else {
			out.println("<tr");
			out.println("<td></td>"); // Blank cell.
			out.println("<td>Total cost:</td>");
			out.println("<td>" + totalCost + "</td>");
			out.println("</tr>");
		}
		out.println("</table>");
		out.println("</center>");
		out.println("</body>");
		out.println("</html>");
		out.flush();
	}
}

这里的关键是取得session中的多条记录，使用session.getAttributeNames()方法。

不得不说，使用servlet做视图的输出非常的费劲。