Java ShoppingCart servlet提供错误？

我无法找到我的webApp有什么问题。这是我的第一个项目，我有点卡住了。我所知道的是，

ShoppingCart.java

每当我在

index.html

中单击“添加到购物车”时，它都会给我一个500系列的错误代码，我试图查看控制台，但没有完全理解。这是一个非常简单的代码，如果你看到什么请告诉我

index.html

比萨饼名称价格添加到购物车
佩佩雷诺
20$  
烧烤
10$
农舍
35$ 

Cart.java

package com.cart;

import java.util.HashMap;

public class Cart {
    HashMap<String, Integer> cartItems;

    public Cart() {
        cartItems = new HashMap<>();
    }

    public HashMap<String, Integer> getItems() {
        return cartItems;
    }

    public void addToCart(String item, Integer price) {
        cartItems.put(item, price);
    }

    public void deleteFromCart(String item) {
        cartItems.remove(item);
    }
}

package com.cartServlet;

import com.cart.*;

@WebServlet("/ShoppingCart")
public class ShoppingCart extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public ShoppingCart() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html");
        HttpSession session = request.getSession();
        Cart shoppingCart = (Cart) session.getAttribute("cart");
        if (shoppingCart == null) {
            shoppingCart = new Cart();
            session.setAttribute("cart", shoppingCart);
        }
        String name = request.getParameter("name");
        Integer price = Integer.parseInt(request.getParameter("price"));
        shoppingCart.addToCart(name, price);
        session.setAttribute("cart", shoppingCart);

        RequestDispatcher dispatch = request.getRequestDispatcher("response.html");
        dispatch.include(request, response);

        HashMap<String, Integer> items = shoppingCart.getItems();

        PrintWriter out = response.getWriter();
        out.println("<table border='1px'>");

        for (String key : items.keySet()) {
            out.println("<tr><td>" + key + " - </td><td>" + "$" + items.get(key) + "</td></tr>");
        }

        out.println("</table>");
    }
}

response.html

比萨饼已成功添加到购物车
将更多比萨饼添加到购物车中
运货马车

web.xml

abc
com.cartServlet.ShoppingCart
abc
/addToCart

日志文件

 Mar 30, 2016 7:42:26 PM org.apache.catalina.core.StandardWrapperValve   invoke
SEVERE: Servlet.service() for servlet [abc] in context with path      [/ShoppingCart] threw exception
    java.lang.IllegalStateException: getOutputStream() has already been called for this response
    at org.apache.catalina.connector.Response.getWriter(Response.java:679)
    at   org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:213)
    at com.cartServlet.ServletCart.doGet(ServletCart.java:46)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

---

我认为您使用的是@WebServlet（“/ShoppingCart”），因此url模式变为 因此，我建议您使用

农舍
35$ 

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希望这对你有用！！：）

您正在混合servlet和JSP。想想你真正需要什么技术。 如果需要，您可以将这些技术结合起来。下面介绍了如何执行此操作：

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请提供日志文件中的例外情况。@tak3shi我已经添加了日志文件，请查看一下……你好，阿披舍克，谢谢你的回答，但你提到的ShoppingCart实际上就是这个web应用程序的名称。。我想您可能会感到困惑，因为我也给了我的servlet相同的名称。。。