hashtable的问题！高手指点

Question

message description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.lang.NullPointerException
java.lang.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:980)
java.lang.Float.valueOf(Float.java:205)
com.cart.processRequest(cart.java:32)
org.apache.jsp.cart_jsp._jspService(cart_jsp.java:82)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.0.27 logs.
--------------------------------------------------------------------------------Apache Tomcat/5.0.27

Answer 1

那你用hashmap试试，他们之间的区别只有，key值hashtable不能为空，hashmap可以为空

Answer 2

NullPointerException
空指针，看看有什么对象可能为空却没有判断

Answer 3

购物车bean源码如下（cart.java）
package com;import java.util.*; 
import com.msgCart;
import javax.servlet.http.*;
public class cart{ 
    
    public Hashtable items; 
    
    public void processRequest(HttpServletRequest clientRequest)
   {
   String id,name,pri,pri1,submit,strNumber;
   int number;
   float price,price1;
   //取得客户端数据
   submit=clientRequest.getParameter("submit");
  
                id=clientRequest.getParameter("id");
   strNumber=clientRequest.getParameter("strNumber");
   pri=clientRequest.getParameter("price");
                pri1=clientRequest.getParameter("price1");
   name=clientRequest.getParameter("name");
                
                price=(Float.valueOf(pri)).floatValue();
                price1=(Float.valueOf(pri1)).floatValue();
   number=(Integer.valueOf(strNumber)).intValue();
                
                
                
                //点击"clear"按钮的情况
   if(submit!=null)
   {
   if(submit.equals("clear"))
   {
   clear();
   return;
   }                                                  //点击"add"按钮的情况
                         if(submit.equals("add"))
                         {                              
                              add(id,number,price,price1,name);
                              //return;
                         }
  
                         //点击"remove"按钮的情况
                         if(submit.equals("remove"))
                         {
                            remove(id);
                         }
  
                            //点击"update"按钮的情况
                         if(submit.equals("update"))
                         {
                            update(id,number);
                         }
      }
    
                
                
            } 
    
    
(msgCart.java)
package com;
import java.util.*; public class msgCart 
{ 
    
    public int pro_count=0;
    public float price=0;
    public float price1=0;
    public String id;
    public String pro_name;
         public msgCart()
    {
       
    }    public void setCart(String id,int number,float price,float price1,String name)    
    {
      this.pro_count=number;
      this.price=price;
      this.price1=price1;
      this.id=id;
      this.pro_name=name;
      
    }         public void addPro(int pc)             //添加商品
    {
        pro_count+=pc;
    }     public void modPro(int mc)            //修改商品数量
    {
        pro_count=mc;
    }         public String getId()                 //返回产品的ID号
    {
        return id;
     }     public int getProcount()           //返回产品的定购数量
    {
        return pro_count;
    }             public float getPrice()             //返回产品原价
    {
        return price;
     }     public float getPrice1()            //返回产品现价
     {
        return price1;
     }      public float getPricecount()         //返回每个产品的订购总价(以现价为准)。
    {
        return price1*pro_count;
    }     public String getProname()           //返回每个产品的名字。
    {
        return pro_name;
    }
   
      }

Answer 4

上边的(cart.java)没贴全重贴如下
package com;import java.util.*; 
import com.msgCart;
import javax.servlet.http.*;
public class cart{ 
    
    public Hashtable items; 
    
    public void processRequest(HttpServletRequest clientRequest)
   {
   String id,name,pri,pri1,submit,strNumber;
   int number;
   float price,price1;
   //取得客户端数据
   submit=clientRequest.getParameter("submit");
  
                id=clientRequest.getParameter("id");
   strNumber=clientRequest.getParameter("strNumber");
   pri=clientRequest.getParameter("price");
                pri1=clientRequest.getParameter("price1");
   name=clientRequest.getParameter("name");
                
                price=(Float.valueOf(pri)).floatValue();
                price1=(Float.valueOf(pri1)).floatValue();
   number=(Integer.valueOf(strNumber)).intValue();
                
                
                
                //点击"clear"按钮的情况
   if(submit!=null)
   {
   if(submit.equals("clear"))
   {
   clear();
   return;
   }                                                  //点击"add"按钮的情况
                         if(submit.equals("add"))
                         {                              
                              add(id,number,price,price1,name);
                              //return;
                         }
  
                         //点击"remove"按钮的情况
                         if(submit.equals("remove"))
                         {
                            remove(id);
                         }
  
                            //点击"update"按钮的情况
                         if(submit.equals("update"))
                         {
                            update(id,number);
                         }
      }  
                
                
            }    
    
    
    
    
    public cart()
    {
        items = new Hashtable();
    }      public void add(String id,int number,float price,float price1,String name)
    {
        String ID=new String(id); 
        msgCart m_cart=new msgCart();
        
        if(items.containsKey(ID))
        {   
            m_cart=(msgCart)items.get(ID);
            m_cart.addPro(number);
        }
        else
        {
             number=1;             
             items.put(ID,m_cart);
             m_cart.setCart(id,number,price,price1,name);        
        }    }       public void update(String id,int num)
     {  
         String ID=new String(id);
        if(items.containsKey(ID))
        {     
            msgCart m_cart=new msgCart();
            m_cart=(msgCart)items.get(ID);
            m_cart.modPro(num);
        }
        else
        {
             System.out.print("no modify pc_count");
         }         }     public void remove(String id)       //删除商品
    {        
        String ID=new String(id); 
        items.remove(ID);
    }       public void clear()              //清空购物车
    {
        items.clear();
    }    
    public Hashtable getCart()   
    {
        return items;
    } 
    public float getCartprice()     //购物车总金额
    {
        Enumeration enum=items.elements();        msgCart m_cart=new msgCart();        float count=0.0f;        while(enum.hasMoreElements())
        {
            m_cart=(msgCart)enum.nextElement();            count+=m_cart.getPricecount();
        }         return count;
     }       }
  

Answer 5

jsp页面如下，从其它页面通过url传递参数到这个页面<jsp:useBean id="mycart" class="com.cart" scope="session"/>
<link href="css.css" rel="stylesheet" type="text/css"> 
 
 <table width="490"  border="1" align="center" cellpadding="0" cellspacing="0" bordercolor="#996600" style="border-collapse: collapse">
<tr>
<td colspan="8">欢迎！</td>
</tr>
<tr>    
    <td width="11%" align="center">商品编码</td>
        <td width="23%" align="center">商品名称</td>
<td width="11%" align="center">商品单价</td>
        <td width="11%" align="center">订购数量</td>                
        <td width="12%" align="center">修改数量</td>
        <td width="11%" align="center">取消订购</td>
        <td colspan="2" align="center">合计</td>    
</tr>
<%
mycart.processRequest(request);  //从购物车Hashtable中得到一个包含所有商品名称的迭代器Hashtable cart=new Hashtable();
cart=mycart.getCart(); Iterator ci = cart.keySet().iterator();

while(ci.hasNext())
{
String ID =(String)ci.next();

if(ID!=null){

com.msgCart mcart=new com.msgCart();
    mcart=(com.msgCart)cart.get("ID");

String name =mcart.getProname();
String id=mcart.getId();
String price=(String)mcart.getPrice();
//String price1=(String)mcart.getPrice1();
//String cartPrice=(String)
//String proPrice
}      
%>


<tr> 
        <td width="11%" align="center"><%=name%></td>
        <td width="23%" align="center"><%=id%></td>
        <td width="11%" align="center"><%=price%></td>
        <td width="11%" align="center"><input name="Number" type="text" value="strNumber" size="6" align="middle"></td>                
        <td width="12%" align="center"><input type="button" name="Submit" value="update" ></td>
        <td width="11%" align="center"><input type="button" name="Submit" value="delect"></td>
        <td width="18%" align="right"><%%></td>
<td width="3%" align="right">元</td>           
</tr>
             
    <tr>
<td colspan="8"><table width="100%" cellpadding="0" cellspacing="0" align="center">
<tr>    
<td width="75%"  align="right">总计:</td>
<td width="23%" align="right"><%%></td>
<td width="2%" align="right">元</td>
</tr>
 </table></td>
</tr>
<%//}%>
<tr>
<td colspan="8"><table width="100%" cellpadding="0" cellspacing="0" align="center">
<tr>
<td width="33%" align="center"><a href="">继续购物</a></td>
<td width="34%" align="center">清空购物车</td>
<td width="33%" align="center"><a href="">前往收银台</a></td>

</tr>
</table></td>
</tr>

<tr>
<td colspan="8" align="center"><a href=# onclick="javasrcript:window.close();">关 闭 窗 口</a></td>
</tr></table>
<% Enumeration a= request.getParameterNames();
while(a.hasMoreElements())
{
  System.out.println(a.nextElement());
}%>

Answer 6

Hashtable不是线程安全的
Hashmap是线程安全的
考虑改成那种吧
其实操作都差不多吧