Servlet.service（）引发了java.lang.NullPointerException java.lang.NullPointerException

严重: 在路径为/Exp3的上下文中，Servlet[Exp3.Servlet117]的Servlet.service（）引发了具有根本原因的异常java.lang.NullPointerException
java.lang.NullPointerException
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
at sun.misc.FloatingDecimal.parseFloat(Unknown Source)
at java.lang.Float.parseFloat(Unknown Source)
at org.apache.jsp._191220117_002dcart_jsp._jspService(_191220117_002dcart_jsp.java:155)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:476)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:713)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:462)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:387)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:315)
at Exp3.Servlet117.doPost(Servlet117.java:66)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:544)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:616)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1634)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
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)
这是出现的问题
servlet117的代码如下：
package Exp3;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**

Servlet implementation class Servlet117

/
@WebServlet("/Servlet117")
public class Servlet117 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**

@see HttpServlet#HttpServlet()
/
public Servlet117() {
super();
// TODO Auto-generated constructor stub
}
public void destroy() {
super.destroy();
}
/**
@see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.getWriter().append("Served at: ").append(request.getContextPath());
}

/**

@see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
HttpSession session=request.getSession(true);
String[][] goods=(String[][])session.getAttribute("MYCART");
if(goods==null) {
}
float total=0;
for(int i=0;i<goods.length;i++) {

  float amount=Float.parseFloat(goods[i][2])*Integer.parseInt(goods[i][3]);
  if(amount==0)
      continue;
  total += amount;

}

  double discount=1;
  if(total >=1000)
      discount=0.85;
  else if(total >=500)
      discount=0.9;
  else if(total >=200)
      discount=0.95;
  else if(total >=100)
      discount=0.98;
  String url="191220117-cart.jsp?DISCOUNT="+discount+"&TOTAL"+total;
  RequestDispatcher rd=request.getRequestDispatcher(url);
  rd.forward(request, response);

}
public void init() throws ServletException{
}
}
以下是cart.jsp的代码：
<%
String cardNo = (String)session.getAttribute("CARDNO");

String[][] goods = (String[][])session.getAttribute("MYCART");

  if (goods != null){
  }    
  
  String strTotal=request.getParameter("TOTAL");
  String strDiscount=request.getParameter("DISCOUNT");
  float total=Float.parseFloat(strTotal);
  double discount=Double.parseDouble(strDiscount);

查看购物车

会员卡号：<%=cardNo %> <%for (int i=0;i <%} %>

          <tr>
              <td colspan = "4" style = "text-align:right;">总金额：</td>
              <td colspan = "1" style = "text-align:right;"><b><%=total %></b></td>
          </tr>
          <tr>
          <td></td>
              <td colspan = "2" style = "text-align:right;">适用折扣：</td>
              <td colspan = "1" style = "text-align:left;"><b><%=discount*100 %>%</b></td>
              <td colspan = "1" style = "text-align:right;">折后金额：</td>
              <td colspan = "1" style = "text-align:right;"><b><%=String.format("%.2f",total*discount) %></b></td>
              </tr>
              <tr>
              <td></td>
              <td colspan = "4" style = "text-align:center;">
              <input type = "submit" value = "&nbsp;确认下单&nbsp;" name = "submit"/>&nbsp;&nbsp;
              <input type = "button" value = "&nbsp;&nbsp;返回&nbsp;&nbsp" name = "goback" onclick = "location='191220117-shop.jsp'"/>&nbsp;&nbsp;
              </td>
          </tr>
      </table>
  </form>

编号	商品名称	单价（元）	进入购物车	选购数量
<%=goods[i][0] %>	<%=goods[i][1] %>	<%=goods[i][2] %>	<%=goods[i][3] %>	<%=amount %>

at Exp3.Servlet117.doPost(Servlet117.java:66)
这个地方空指针异常，打断点看看