CODEWITHSUNDEEP
javahtmltimezonejodatime
Stephen Reed
Stephen Reed

Reputation: 197

How to obtain a complete HTML timezone selection that is compatible with a Joda DateTime backend

The JodaTime DateTimeZone class provides the getAvailableIDs method to list the timezone identifiers supplied by the Java platform. Is there a plain HTML select tag and options listing the compatible timezone identifiers?

Upvotes: 0

Views: 35

Answers (2)

Stephen Reed
Stephen Reed

Reputation: 197

The resulting HTML is too large to post here, but the following utility generates the desired HTML select and option tags...

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import org.joda.time.DateTimeZone;

public class DateTimeUtils {

  /**
   * Prevents the construction of instances of this utility class which has only static methods.
   */
  private DateTimeUtils() {
  }

  /**
   * Displays the timezone identifiers provided by the system.
   */
  public static void listAvailableIDs() {
    final Set<String> availableIDs = DateTimeZone.getAvailableIDs();
    final List<String> sortedAvailableIDs = new ArrayList<>();
    sortedAvailableIDs.addAll(availableIDs);
    Collections.sort(sortedAvailableIDs);
    for (final String sortedAvailableID : sortedAvailableIDs) {
      System.out.println(sortedAvailableID);
    }
  }

  /**
   * Generates an HTML select element for the timezone identifiers accepted by Joda DateTime on Java 15.
   */
  public static void generateHTMLTimezoneSelect() {
    final Set<String> availableIDs = DateTimeZone.getAvailableIDs();
    final List<String> sortedAvailableIDs = new ArrayList<>();
    sortedAvailableIDs.addAll(availableIDs);
    Collections.sort(sortedAvailableIDs);
    final StringBuilder stringBuilder = new StringBuilder();
    stringBuilder
            .append("<label for=\"timezone\">Select your timezone:</label>\n")
            .append("<select name=\"timezone\">\n");
    for (final String sortedAvailableID : sortedAvailableIDs) {
      stringBuilder
              .append("  <option value=\"")
              .append(sortedAvailableID)
              .append("\">")
              .append(sortedAvailableID)
              .append("</option>\n");
    }
    stringBuilder.append("</select>\n");
    System.out.println(stringBuilder.toString());
  }

  /**
   * Generates an initialized String array for the timezone identifiers accepted by Joda DateTime on Java 15.
   */
  public static void generateTimezoneIDArray() {
    final Set<String> availableIDs = DateTimeZone.getAvailableIDs();
    final List<String> sortedAvailableIDs = new ArrayList<>();
    sortedAvailableIDs.addAll(availableIDs);
    Collections.sort(sortedAvailableIDs);
    final StringBuilder stringBuilder = new StringBuilder();
    stringBuilder
            .append("  private static final String[] TIMEZONE_IDS = {\n");
    for (final String sortedAvailableID : sortedAvailableIDs) {
      stringBuilder
              .append("    \"")
              .append(sortedAvailableID)
              .append("\",\n");
    }
    stringBuilder.setLength(stringBuilder.length() - 2);
    stringBuilder.append("\n  };\n");
    System.out.println(stringBuilder.toString());
  }
}

Upvotes: 0

Adam Michalik
Adam Michalik

Reputation: 9945

There is no such tag in the HTML standard. You must either generate the list in the backend or using one of the available frontend libraries (eg. https://momentjs.com/timezone/). Generating in the backend gives you a guarantee that the identifiers are compatible.

Upvotes: 1

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