assertThat(new SimpleDateFormat("yyyy/MM/dd HH:mm:ss").format(date), is("2010/09/07 11:49:00"));
    }

    /**
     * @throws Exception
     */
    @Test
    public void testToDate_MediumStyle() throws Exception {
        final Date date = toDate("2010/9/7 11:49:10", Locale.JAPAN);
        assertThat(new SimpleDateFormat("yyyy/MM/dd HH:mm:ss").format(date), is("2010/09/07 11:49:10"));
    }

                                                            pattern="yyyy-MM-dd'T'HH:mm:ss"/></td>
                                                    <td><c:if test="${data.endTime!=null}">
                                                        <fmt:formatDate value="${fe:date(data.endTime)}"
                                                                        pattern="yyyy-MM-dd'T'HH:mm:ss"/>

                                                 title="yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
                                                 data-validation="custom"
                                                 data-validation-regexp="(^$|^[1-9]\d{3}\-\d\d\-\d\dT\d\d\:\d\d\:\d\d\.\d{3}Z$)"
                                                 data-validation-help="yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"/>
                                    </div>

Integer nullValue = IntegerConversionUtil.toInteger(null);     // Returns null
Boolean flag = BooleanConversionUtil.toBoolean("true");        // Returns true
Date date = DateConversionUtil.toDate("2023-12-25", "yyyy-MM-dd");

// Primitive conversions with default values
int primitiveInt = IntegerConversionUtil.toPrimitiveInt(value, "0");  // Default to 0 if null
```

### Collection Utilities with Java 21 Support
```java

    <function-class>org.codelibs.fess.taglib.FessFunctions</function-class>
    <function-signature>java.util.Date parseDate(java.lang.String, java.lang.String)</function-signature>
    <example>
      ${fe:parseDate(doc.tstamp, "yyyy-MM-dd HH:mm:ss")}
    </example>
  </function>

  <function>
    <description>
      Returns formatted duration from a given value.
    </description>
    <name>formatDuration</name>

 * <td>{@link DateFormat#SHORT} format</td>
 * <td>{@literal yy/MM/dd}</td>
 * </tr>
 * <tr>
 * <td>{@link DateFormat#MEDIUM} format</td>
 * <td>{@literal yyyy/MM/dd}</td>
 * </tr>
 * <tr>
 * <td>{@link DateFormat#LONG} format</td>
 * <td>{@literal yyyy/MM/dd}</td>
 * </tr>
 * <tr>
 * <td>{@link DateFormat#FULL} format</td>
 * <td>{@literal yyyy'nen'M'gatsu'd'nichi'}</td>
 * </tr>
 * <tr>

                                                                value="${fe:date(data.lastAccessTime)}"
                                                                pattern="yyyy-MM-dd'T'HH:mm:ss"/></td>
                                                    </tr>
                                                </c:forEach>
                                                </tbody>

 * </tr>
 * <tr>
 * <td>{@link DateFormat#MEDIUM} format</td>
 * <td>{@literal yyyy/MM/dd H:mm:ss}</td>
 * </tr>
 * <tr>
 * <td>{@link DateFormat#LONG} format</td>
 * <td>{@literal yyyy/MM/dd H:mm:ss z}</td>
 * </tr>
 * <tr>
 * <td>{@link DateFormat#FULL} format</td>
 * <td>{@literal yyyy'年'M'月'd'日' H'時'mm'分'ss'秒' z}</td>
 * </tr>
 * </table>
 *
 * @author shinsuke
 * @see DateConversionUtil

                                                    <td><fmt:formatDate
                                                            value="${fe:date(data.createdTime)}"
                                                            pattern="yyyy-MM-dd'T'HH:mm:ss"/></td>
                                                </tr>
                                            </c:forEach>
                                            </tbody>

    protected boolean isValidDateFormat(final String date) {
        if (date == null || date.isEmpty()) {
            return true; // Date is optional
        }
        // Basic validation for W3C Datetime format (YYYY-MM-DD or YYYY-MM-DDThh:mm:ss+00:00)
        // This is a simplified validation
        if (date.length() < 10) {
            if (logger.isDebugEnabled()) {
                logger.debug("Invalid date format (too short): {}", date);