Question

We store our dates are stored in milliseconds since the epoch and the Olson time zone ID for the objects we want to display time related data about.

How can I convert the Olson TZID to a TimeZoneConstant to create a TimeZone and use DateTimeFormat?

// values from database
String tzid = "America/Vancouver";
long date = 1310771967000L;


final TimeZoneConstants tzc = GWT.create(TimeZoneConstants.class);
String tzInfoJSON = MAGIC_FUNCTION(tzid, tzc);
TimeZone tz = TimeZone.createTimeZone(TimeZoneInfo.buildTimeZoneData(tzInfoJSON));
String toDisplay = DateTimeFormat.getFormat("y/M/d h:m:s a v").format(new Date(date), tz); 

Does that MAGIC_FUNCTION exist? Or is there another way to do this?

Answer 1

Doing a GWT.create on the TimeZoneConstants class is bad game according to the GWT Javadoc [1]. So what I did was create a class on the server-side that parses /com/google/gwt/i18n/client/constants/TimeZoneConstants.properties and builds a cache of all the JSON objects for each time zone (indexed by their Olson TZID).

My site is running on jboss, so I copied TimeZoneConstants.properties into my site’s war/WEB-INF/lib directory (probably didn’t need to copy it there since the GWT jars are already there). Then I have a singleton class that does the parsing when constructed:

InputStream inStream = Thread.currentThread().getContextClassLoader().getResourceAsStream(PROPERTIES_FILE);
InputStreamReader isr = new InputStreamReader(inStream);
BufferedReader br = new BufferedReader(isr); 
for (String s; (s = br.readLine()) != null;) { 
  // using a regex to grab the id to use as a key to the hashmap
  // a full json parser here would be overkill
  Pattern pattern = Pattern.compile("^[A-Za-z]+ = (.*\"id\": \"([A-Za-z_/]+)\".*)$");
  Matcher matcher = pattern.matcher(s);     
  if (matcher.matches()) {
    String id = matcher.group(2);
    String json = matcher.group(1);

    if (!jsonMap.containsKey(id)) {
      jsonMap.put(id, json);
    }
  }
} 
br.close();
isr.close();
inStream.close();

Finally I make an RPC call to get the TimeZoneInfoJSON to the client (assuming the server knows which TimeZoneID I’m interested in):

getTimeZone(new PortalAsyncCallback<String>() {
  public void onSuccess(String tzJson) {
    timeZone = TimeZone.createTimeZone(TimeZoneInfo.buildTimeZoneData(tzJson));
  }
});

Not the most elegant solution but it has given me a way to display dates and times for a specific time zone over DST transitions.

[1] http://google-web-toolkit.googlecode.com/svn/javadoc/2.0/com/google/gwt/i18n/client/constants/TimeZoneConstants.html