根据键返回列表过滤HashMap

Question

I have a HashMap with key, values that are strings. I would like to filter the HashMap by the key values that start with the string " locationId " and return the values in the keys to an array list of strings. This is how the HashMap is populated:

HashMap<String, String> hm = new HashMap<String, String>();
hm.put("locationId2", rs.getString("ORG_Id"));
hm.put("locationType2", rs.getString("ORG_Type"));
hm.put("StartDate2", rs.getString("START_DT_TM_GMT"));


hm.put("locationId3", rs.getString("ORG_Id"));
hm.put("locationType3", rs.getString("ORG_Type"));
hm.put("StartDate3", rs.getString("START_DT_TM_GMT"));


hm.put("locationId4", rs.getString("ORG_Id"));
hm.put("locationType4", rs.getString("ORG_Type"));
hm.put("StartDate4", rs.getString("START_DT_TM_GMT"));


hm.put("locationId5", rs.getString("ORG_Id"));
hm.put("locationType5", rs.getString("ORG_Type"));
hm.put("StartDate5", rs.getString("START_DT_TM_GMT"));

I need the ORG_Id values in an arraylist.

List<String> facilityIds = hm.entrySet().stream().filter(x -> x.getKey().startsWith("locationId")).collect(map -> map.values());

I can't find where I can put the values into a string list. The compile error is that it does not recognize the values() method.

UPDATE Also tried putting the filtered Hashmap into another HashMap like this:

HashMap<String, String>  facilityIds = currentOperatingSchedules.entrySet().stream().filter(map -> map.getKey().startsWith("locationId")).collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue()));

But get the compilation error that it does not recognize getKey() and getValue()

Answer 1

This should work. It works as follows:

1. Get the entrySet of the map and create a stream.
2. filter on the key that starts with locationId
3. And collect those values into a list.

         List<String> list = hm.entrySet().stream()
                      .filter(e->e.getKey().startsWith("locationId"))
                      .map(e->e.getValue())
                      .collect(Collectors.toList());