*
 * <dl>
 *   <dt>The IPv4 loopback address, {@code "127.0.0.1"}.
 *   <dd>{@code 7f 00 00 01}
 *   <dt>The IPv6 loopback address, {@code "::1"}.
 *   <dd>{@code 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01}
 *   <dt>From the IPv6 reserved documentation prefix ({@code 2001:db8::/32}), {@code "2001:db8::1"}.
 *   <dd>{@code 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 01}

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-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>

 *
 * <dl>
 *   <dt>The IPv4 loopback address, {@code "127.0.0.1"}.
 *   <dd>{@code 7f 00 00 01}
 *   <dt>The IPv6 loopback address, {@code "::1"}.
 *   <dd>{@code 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01}
 *   <dt>From the IPv6 reserved documentation prefix ({@code 2001:db8::/32}), {@code "2001:db8::1"}.
 *   <dd>{@code 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 01}

 * so you can specify multiple options using method chaining.
 * </p>
 *
 * <pre>
 * copyBeanToBean(srcBean, destBean, excludeNull().dateConverter("date", "MM/dd"));
 * </pre>
 *
 * @author koichik
 */
public abstract class CopyOptionsUtil {

    /**
     * Do not instantiate.
     */
    protected CopyOptionsUtil() {
    }

    /**

                                                    </td>
                                                    <td>${f:h(data.size)}</td>
                                                    <td>${fe:formatDate(data.lastModified, 'yyyy-MM-dd HH:mm:ss')}</td>
                                                </c:if>
                                                <c:if test="${data.directory.booleanValue()}">

    private String loc;

    /**
     * The date of last modification of the file. This date should be in W3C
     * Datetime format. This format allows you to omit the time portion, if
     * desired, and use YYYY-MM-DD.
     *
     * Note that this tag is separate from the If-Modified-Since (304) header
     * the server can return, and search engines may use the information from
     * both sources differently.
     */

        final MyBean src = new MyBean();
        src.aaa = "2008/01/17";
        final MyBean2 dest = new MyBean2();
        BeanUtil.copyBeanToBean(src, dest, converter(new DateConverter("yyyy/MM/dd")));
        System.out.println(dest.aaa);
        assertThat(dest.aaa, is(notNullValue()));
    }

    /**
     * @throws Exception
     */
    @Test

 * </pre>
 * <p>
 * Multiple options can also be specified using method chaining.
 * </p>
 *
 * <pre>
 * copyBeanToBean(srcBean, destBean, excludeNull().dateConverter("date", "MM/dd"));
 * </pre>
 *
 * @author Kimura Satoshi
 * @author higa
 * @author shinsuke
 * @see CopyOptionsUtil
 * @see CopyOptions
 */
public abstract class BeanUtil {

    /**
     * Do not instantiate.

    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);