Build map with column name and column values from java.sql.ResultSet

I have the following snippet:

    Connection connection = getConnection(schemaName);
    Statement stmt = connection.createStatement();
    String sql = "SELECT * FROM " + tableName;
    ResultSet rs = stmt.executeQuery(sql);

now what I want to achieve is building a

Map<String , List<String>>

where key is the columnName and value is list of columnValues. Here is my code:

    ResultSetMetaData rsmd = rs.getMetaData();
    int columnCount = rsmd.getColumnCount();

    List<String> columnNames = new LinkedList<>();
    for (int i = 1; i <= columnCount; i++) {
        columnNames.add(rsmd.getColumnName(i));
    }

    Map<String, List<String>> columnNameToValuesMap = new HashMap<String, List<String>>();

    for (String columnName : columnNames) {
        List<String> values = new ArrayList<>();
        try {
            while (rs.next()) {
                values.add(rs.getString(columnName));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        columnNameToValuesMap.put(columnName, values);
    }

The issue is that after the first columnName iteration, rs.next() is empty. So basically The result map contains the values for only the first column. How can I reuse the same resultSet for each iteration ? Why its empty after the first one ?

You can follow the below steps:

1. Initialise the columnNameToValuesMap with empty list objects with column name as key

2. Iterate the resultset using rs.next()

3. Get each column data using a for loop and add to list values object

4. Add the list of columns data to columnNameToValuesMap object

You can refer the below code with comments:

List<String> columnNames = new LinkedList<>();
Map<String,List<String>> columnNameToValuesMap=new HashMap<String, List<String>>();

for (int i = 1; i <= columnCount; i++) {
       String columnName = rsmd.getColumnName(i);
       columnNames.add(columnName);

       //Load the Map initially with keys(columnnames) and empty list
       columnNameToValuesMap.put(columnName, new ArrayList());
}

try {
   while (rs.next()) { //Iterate the resultset for each row

     for (String columnName : columnNames) {
        //Get the list mapped to column name
        List<String> columnDataList = columnNameToValuesMap.get(columnName);

         //Add the current row's column data to list
         columnDataList.add(rs.getString(columnName));

         //add the updated list of column data to the map now
         columnNameToValuesMap.put(columnName, columnDataList);
       }
    }
} catch (SQLException e) {
   e.printStackTrace();
}