MessageHelper.java 文件源码

/**
 * Represents a factory method to instantiate {@code MessageHelper} singleton following by
 * "Double Checked Locking & Volatile" pattern.
 *
 * @param messageSource {@code MessageSource} used as the underlying messages bundle
 * @return {@code MessageHelper}
 */
public static MessageHelper singleton(final MessageSource messageSource) {
    MessageHelper helper = instance;
    if (helper == null) {
        synchronized (MessageHelper.class) {
            helper = instance;
            if (helper == null) {
                Assert.notNull(messageSource);
                instance = new MessageHelper(messageSource);
                helper = instance;
            }
        }
    }
    return helper;
}