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电梯直达

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发表于 2003-05-31 21:30 |只看该作者 |倒序浏览

sqlCommand1="SELECT * FROM MESSAGE_PROMM";
   rs1=add_message.executeQuery(sqlCommand1);
   while(rs1.next())
   {
   promm_id=rs1.getString("Id"

;
promm_content=rs1.getString("

romm"

;
   out.println(""+promm_content);
   sqlCommand2="SELECT * FROM MESSAGE_CLASS WHERE Promm="+promm_id;
   rs2=add_message.executeQuery(sqlCommand2);
   while(rs2.next())
   {
   class_id=rs2.getString("Id"

;
class_content=rs2.getString("Content"

;
   out.println(""+class_id);
   out.println(""+class_content);
   }
   }
我在一个查询中加了查询，为什么老是提示：Root cause:
java.lang.NullPointerException
请高手指教！

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badseed

丰衣足食

论坛徽章:: 0

2楼 [报告]

发表于 2003-05-31 21:53 |只看该作者

一个查询中加了查询为什么会出现这种错误

每次在查询前最好先调用prepareStatement()方法，
Connection con = dataSource.getConnection();
PreparedStatement pst =null;
String sqlStatement1="SELECT * FROM MESSAGE_PROMM";
pst = con.prepareStatement(sqlStatement1);
ResultSet rset1 = pst.executeQuery();

String sqlStatement2="SELECT * FROM MESSAGE_CLASS WHERE Promm="+promm_id;
pst = con.prepareStatement(sqlStatement2);
ResultSet rset2 = pst.executeQuery();