我正在尝试将数据加载到哈希映射的哈希映射中，并且我不断收到空指针并且不确定我是否在做正确的事情。
我希望我的哈希映射基于三个键 SalesAreaCode、year 和 product。我想将其余部分存储在arraylist中。我想传递销售区号、年份和产品，并列出与这三个键相关的所有产品，例如客户、数量、价格：我真的需要帮助或有人指出我正确的方向。任何帮助将不胜感激！！艾伦
代码：
public HashMap<String, HashMap<String, HashMap<String, ArrayList<Sales>>>> getSalesDetails(Connection con)
{
HashMap<String, HashMap<String, HashMap<String, ArrayList<Sales>>>>> hmpSales =
new HashMap<String, HashMap<String, HashMap<String, ArrayList<Sales>>>>>();
Sales s;
HashMap<String,ArrayList<Sales>> hmpSalProd = new HashMap<String, ArrayList<Sales>>();
HashMap<String,HashMap<String,ArrayList<Sales>>> hmpSalYear =
new HashMap<String, ArrayList<Sales>>>();
try
{
pst = con.prepareStatement(sql);
rs=pst.executeQuery();
while(rs.next())
{
s=new Sales();
if(!(hmpSalProd.containskey(rs.getString("product"))))
{
s.setSalesCode(rs.getString("sacd"));
s.setCustomerCode(rs.getString("custcd"));
s.setYear(rs.getInt("year"));
s.setProduct(rs.getString("product"));
s.setPrice(rs.getDouble("price"));
s.setQty(rs.getInt("qty"));
hmpSalProd.put(rs.getString("product"),
new ArrayList<Sales>(Arrays.asList(s)));
}
else
{
s.setSalesCode(rs.getString("sacd"));
s.setCustomerCode(rs.getString("custcd"));
s.setYear(rs.getInt("year"));
s.setProduct(rs.getString("product"));
s.setPrice(rs.getDouble("price"));
s.setQty(rs.getInt("qty"));
hmpSalProd.get(rs.getString("product")).add(s);
}
if(!(hmpSalYear.containsKey(String.valueOf(rs.getInt("year")))))
{
hmpSalYear.put(String.valueOf(rs.getInt("year")),hmpSalProd);
}
else
{
hmpSalYear.get(String.valueOf(rs.getInt("year"))).
get(rs.getString("product")).add(s);
}
if(!(hmpSalArea.containsKey(rs.getString("sacd"))))
{
hmpSales.put(rs.getString("sacd"),hmpSalYear);
}
else
{
hmpSales.get(rs.getString("sacd")).
get(String.valueOf(rs.getInt("year"))).
get(rs.getString("product")).add(s);
}
}
pst.close();
rs.close();
}
catch(SQLException se)
{
System.out.println("error loading: " + se.getMessage());
}
return hmpSales;
}