如何在Hashtable列表中转换ResultSet？

Question

Well, that must be an easy one but I can't find the solution anywhere. And I am still not enough comfortable using Java to figure out the way to do it.

So far, I am able to loop through a ResultSet and I'm quite proud of myself already.

I would like a List so I could simply loop through it and then call something like myRow.get('ColumnName'); .

Also, there MIGHT another data type instead of a Hashtable to store the key/value. Any tips?

Thank you very much!

Answer 1

myRow.get('ColumnName'); is already in ResultSet , see getObject(String columnLabel) . Now, one difference between ResultSet and Map is that a ResultSet is not (always) random access . Once you go past a row, using ResultSet.next() , it may not allow you to "rewind" to the previous row. There is good reason for this: the number of elements in ReusltSet can be arbitrarily large and the memory requirement on a list of map would be prohibitive.

If you do decide to convert it to a List<Map<String, Object>> then you should create your own implementation of both the List and the Map , such that a Map<String /*columnName*/, Integer /*Index*/> is gives the index of a column-name in each array. I am speaking from experience, I had to change an implementation where a iterating through list of column names was too expensive.

Answer 2

I would use HashMap . Hashtable is old school...

Example:

HashMap<String, Object> p = new HashMap<String, Object>();
p.put("ResultSetkey1","ResultSetvalue1");
p.put("ResultSetkey2","ResultSetvalue2");

Answer 3

what I understand it would be something like this:

LinkedList<HashTable<String,String>> list = new LinkedList<>();


while(rs.next()){
    Hashtable<String, String> currentRowMap = new Hashtable<>();

    ResultSetMetaData rsmd = rs.getMetaData();
    int columnCount = rsmd.getColumnCount();
    for (int i = 1; i <= columnCount; i++) {
        // retrieves column name and value.
        String key = rsmd.getColumnLabel(i);
        String value = rs.getString(rsmd.getColumnName(i));
        if (value == null) {
            value = "null";
        }
        // builds map.
        currentRowMap .put(key, value);
    }
    list.add(currentRowMap);
}

return list;