MySQLNonTransientConnectionException的PreparedStatement Close问题：

Question

我无法找到发生以下异常的位置。我在循环结束后关闭了PreparedStatement，但在调用sendBill方法时它仍然给出了错误：

例外文字：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException:
 No operations allowed after statement closed.
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
 at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
 at com.mysql.jdbc.Util.getInstance(Util.java:386)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
 at com.mysql.jdbc.StatementImpl.checkClosed(StatementImpl.java:461)

相关代码：

void executeBills()
{
    try{
        PreparedStatement preStatementUpdate = null;
        PreparedStatement preStatementInsert = null;

        if(preStatementUpdate==null || preStatementUpdate.isClosed())
                    preStatementUpdate = con.prepareStatement(sqlUpdatequery);

        if(preStatementInsert==null || preStatementInsert.isClosed())
            preStatementInsert = con.prepareStatement(sqlInsertQuery);


        for(int i=0;i<countrylist.size();i++)
        {
            country=countrylist.get(i);

            //Error shown on this line no. 
            sendBill(country,preStatementUpdate,preStatementInsert)

        }

    }catch(Exception e) {
        e.printStackTrace();
    }finally{
        //closing PreparedStatement
        preStatementUpdate.close();
        preStatementInsert.close();
    }

}

void sendBill(String country, PreparedStatement _1, PreparedStatement _2)
{

    //Code of PreparedStatement setting String parameter.. 

    //...error shown on this line no. 
     //getCreditAmount returns int,  so String.valueOf is used
     _1.setString(1,String.valueOf(country.getCreditAmount()));   

    _1.executeUpdate() ;  
    _2.executeUpdate();


     //No closing preparedStatement Here

}