How to populate the dropdown list from sql server database using LinkedHashMap in java

问题

In SQL Server database I have a table which has three columns namely Ref_Name,Ref_from and Ref_to.Now I want a dropdown list to hold values row-wise i.e all column values of the row should be in the dropdown list in following way:-

Reference-1(2014-10-10 07:17:00.000 to 2014-10-10 08:46:00.000)

Reference-2(2014-09-01 10:00:00.000 to 2014-09-01 11:00:00.000)

For this I have used LinkedHashMap as:-

    public LinkedHashMap<String, List<String>> connect()
    {
        ArrayList<String> list = new ArrayList<String>();
        try
        { 
            con = getConnection();
            stmt = con.createStatement();
            String sql="select Ref_No,From_Date,To_Date from Ref_time";
            stmt.executeQuery(sql);
            rs = stmt.getResultSet();
            while (rs.next()) 
            {
                list.add(rs.getString(2));
                list.add(rs.getString(3));
                ref.put(rs.getString(1), list);
            }

        }
        catch( Exception e )
        {
            System.out.println("\nException "+e);
        }
        finally
        {
            //closeConnection(stmt, rs, con);
        }
         return ref;
    }

When I use it in jsp as

<select name="ref_logtime">
<c:forEach var="aff" items="${obj.connect()}">
<option value="${aff.key}">${aff.key}</option>
<option value="${aff.value}">${aff.value}</option>
</c:forEach>
</select>

Then in dropdown ,I get values as:-

 Reference-1
 All datetime entries are shown here
 Reference-2
 All datetime entries are shown here

But I want my dropdown list to have values row wise.How to do that?

回答1:

There are two problems with your code. First, every reference mapping needs to have its own List. Currently, the list is being shared and hence both the reference entries would show all the dates. Change the code as

rs = stmt.executeQuery(sql);
while (rs.next()) 
{
    List<String> list = new ArrayList<String>();
    list.add(rs.getString(2));
    list.add(rs.getString(3));
    ref.put(rs.getString(1), list);
}

The second problem is with the JSTL tag. You need only one <option> tag within the loop which would run twice for you (because you have two reference entries coming from the database) to generate the two <option> tag entries.

<select name="ref_logtime">
  <c:forEach var="aff" items="${obj.connect()}">
    <option value="${aff.key}">${aff.key} ${aff.value}</option>
  </c:forEach>
</select>

来源：https://stackoverflow.com/questions/28407312/how-to-populate-the-dropdown-list-from-sql-server-database-using-linkedhashmap-i

标签

java

sql-server

jstl

html.dropdownlistfor

linkedhashmap