Spring周边：StringTokenizer

public StringTokenizer(String str, String delim, boolean returnDelims){
    // An instance of StringTokenizer behaves in one of two ways, 
    // depending on whether it was created with the returnDelims flag 
    // having the value true or false:
    // 1. If the flag is false, delimiter characters serve to separate tokens. 
    //    A token is a maximal sequence of consecutive characters that are not delimiters.
    // 2. If the flag is true, delimiter characters are themselves considered to be tokens. 
    //    A token is thus either one delimiter character, 
    //    or a maximal sequence of consecutive characters that are not delimiters.
}
public StringTokenizer(String str, String delim) {
    this(str, delim, false);
}
public StringTokenizer(String str) {
    this(str, " \t\n\r\f", false);
}

// Tests if there are more tokens available from this tokenizer's string.
public boolean hasMoreTokens() { ... }
// Returns the next token from this string tokenizer.
public String nextToken() { ... }

// Returns the same value as the hasMoreTokens method.
public boolean hasMoreElements() {return hasMoreTokens();}
// Returns the same value as the nextToken method, 
// except that its declared return value is Object rather than String.
public Object nextElement() {return nextToken();}

  /**
   * Tokenize the given {@code String} into a {@code String} array via a
   * {@link StringTokenizer}.
   * <p>Trims tokens and omits empty tokens.
   * <p>The given {@code delimiters} string can consist of any number of
   * delimiter characters. Each of those characters can be used to separate
   * tokens. A delimiter is always a single character; for multi-character
   * delimiters, consider using {@link #delimitedListToStringArray}.
   * @param str the {@code String} to tokenize (potentially {@code null} or empty)
   * @param delimiters the delimiter characters, assembled as a {@code String}
   * (each of the characters is individually considered as a delimiter)
   * @return an array of the tokens
   * @see java.util.StringTokenizer
   * @see String#trim()
   * @see #delimitedListToStringArray
   */
  public static String[] tokenizeToStringArray(@Nullable String str, String delimiters) {
    return tokenizeToStringArray(str, delimiters, true, true);
  }

  /**
   * Tokenize the given {@code String} into a {@code String} array via a
   * {@link StringTokenizer}.
   * <p>The given {@code delimiters} string can consist of any number of
   * delimiter characters. Each of those characters can be used to separate
   * tokens. A delimiter is always a single character; for multi-character
   * delimiters, consider using {@link #delimitedListToStringArray}.
   * @param str the {@code String} to tokenize (potentially {@code null} or empty)
   * @param delimiters the delimiter characters, assembled as a {@code String}
   * (each of the characters is individually considered as a delimiter)
   * @param trimTokens trim the tokens via {@link String#trim()}
   * @param ignoreEmptyTokens omit empty tokens from the result array
   * (only applies to tokens that are empty after trimming; StringTokenizer
   * will not consider subsequent delimiters as token in the first place).
   * @return an array of the tokens
   * @see java.util.StringTokenizer
   * @see String#trim()
   * @see #delimitedListToStringArray
   */
  public static String[] tokenizeToStringArray(
      @Nullable String str, String delimiters, boolean trimTokens, boolean ignoreEmptyTokens) {

    if (str == null) {
      return new String[0];
    }

    StringTokenizer st = new StringTokenizer(str, delimiters);
    List<String> tokens = new ArrayList<>();
    while (st.hasMoreTokens()) {
      String token = st.nextToken();
      if (trimTokens) {
        token = token.trim();
      }
      if (!ignoreEmptyTokens || token.length() > 0) {
        tokens.add(token);
      }
    }
    return toStringArray(tokens);
  }

// Bean 的 name 属性可以使用 ","、";"、" "作为分隔符。
public static final String MULTI_VALUE_ATTRIBUTE_DELIMITERS = ",; ";

@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
    // 获取 id 属性值
    String id = ele.getAttribute(ID_ATTRIBUTE);
    
    // 获取 name 属性值
    String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

    // 先将 name 属性值全部解析为 aliases
    List<String> aliases = new ArrayList<>();
    if (StringUtils.hasLength(nameAttr)) {
      String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
      aliases.addAll(Arrays.asList(nameArr));
    }

    // 若 id 属性值为空：
    // 将 name 属性的第一个值作为 beanName
    // 将 name 属性的其余值作为 aliases
    String beanName = id;
    if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
      beanName = aliases.remove(0);
      if (logger.isTraceEnabled()) {
        logger.trace("No XML 'id' specified - using '" + beanName +
            "' as bean name and " + aliases + " as aliases");
      }
    }
    
    ....
}