html.java

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     * The <sub> tag
     */
    public static final Tag SUB = new Tag("sub");

    /**
     * The <sup> tag
     */
    public static final Tag SUP = new Tag("sup");

    /**
     * The <table> tag , block tag.
     */
    public static final Tag TABLE = new Tag("table", BLOCK);

    /**
     * The <td> tag , breaks flow, block tag.
     */
    public static final Tag TD = new Tag("td", BREAKS | BLOCK);

    /**
     * The <textarea> tag , preformatted.
     */
    public static final Tag TEXTAREA = new Tag("textarea", PREFORMATTED);

    /**
     * The <th> tag , breaks flow, block tag.
     */
    public static final Tag TH = new Tag("th", BREAKS | BLOCK);

    /**
     * The <title> tag , breaks flow, block tag.
     */
    public static final Tag TITLE = new Tag("title", BREAKS | BLOCK);

    /**
     * The <tr> tag , block tag.
     */
    public static final Tag TR = new Tag("tr", BLOCK);

    /**
     * The <tt> tag
     */
    public static final Tag TT = new Tag("tt");

    /**
     * The <u> tag
     */
    public static final Tag U = new Tag("u");

    /**
     * The <ul> tag , breaks flow, block tag.
     */
    public static final Tag UL = new Tag("ul", BREAKS | BLOCK);

    /**
     * The <var> tag
     */
    public static final Tag VAR = new Tag("var");

    /* Special tags */

    /**
     * Total number of syntetic tags, delared in the Tag class.
     * This must be adjusted if the new synthetic tags are declared.
     * Otherwise the HTML.getAllTags() will not work as expected.
     */
    private static final int TOTAL_SYNTHETIC_TAGS = 3;

    /**
     * All comments are labeled with this tag.
     * This tag is not included into the array, returned by getAllTags().
     * toString() returns 'comment'. HTML reader synthesizes this tag.
     */
    public static final Tag COMMENT = new Tag("comment", SYNTHETIC);

    /**
     *  All text content is labeled with this tag.
     *  This tag is not included into the array, returned by getAllTags().
     *  toString() returns 'content'. HTML reader synthesizes this tag.
     */
    public static final Tag CONTENT = new Tag("content", SYNTHETIC);

    /**
     * All text content must be in a paragraph element.
     * If a paragraph didn't exist when content was encountered,
     * a paragraph is manufactured.
     * toString() returns 'p-implied'. HTML reader synthesizes this tag.
     */
    public static final Tag IMPLIED = new Tag("p-implied", SYNTHETIC);
    final String name;
    final int flags;

    /**
     * Create the unitialised instance of HTML.Tag.
     *
     * The {@link #breaksFlow()}, {@link #isBlock()}
     * and {@link #isPreformatted()} will always return false.
     * The {@link #toString()} will return <code>null</code>.
     *
     * @since 1.3
     */
    public Tag()
    {
      name = null;
      flags = 0;
    }

    /**
     * Creates a new Tag with the specified id, and with causesBreak
     * and isBlock set to false.
     */
    protected Tag(String id)
    {
      name = id;
      flags = 0;
    }

    /**
     * Creates a new Tag with the specified tag name and
     * causesBreak and isBlock properties.
     */
    protected Tag(String id, boolean causesBreak, boolean isBlock)
    {
      int f = 0;

      if (causesBreak)
        {
          f |= BREAKS;
        }

      if (isBlock)
        {
          f |= BLOCK;
        }

      flags = f;
      name = id;
    }

    /**
     * Create a tag taking flags.
     */
    Tag(String id, int a_flags)
    {
      name = id;
      flags = a_flags;
    }

    /**
     * Returns true if this tag is a block tag, which is a tag used to
     * add structure to a document.
     */
    public boolean isBlock()
    {
      return (flags & BLOCK) != 0;
    }

    /**
     * Returns true if this tag is pre-formatted, which is true if
     * the tag is either PRE or TEXTAREA
     */
    public boolean isPreformatted()
    {
      return (flags & PREFORMATTED) != 0;
    }

    /**
     * Returns true if this tag causes a line break to the flow of text
     */
    public boolean breaksFlow()
    {
      return (flags & BREAKS) != 0;
    }

    /**
     * Calls compareTo on the tag names (Strings)
     */
    public int compareTo(Object other)
    {
      return name.compareTo(((Tag) other).name);
    }

    /**
     * The tags are equal if the names are equal (ignoring case).
     */
    public boolean equals(Object other)
    {
      if (other == this)
        {
          return true;
        }

      if (!(other instanceof Tag))
        {
          return false;
        }

      Tag that = (Tag) other;

      return that.name.equalsIgnoreCase(name);
    }

    /**
     * Returns the hash code which corresponds to the string for this tag.
     */
    public int hashCode()
    {
      return name == null ? 0 : name.hashCode();
    }

    /**
     * Returns the tag name. The names of the built-in tags are always
     * returned in lowercase.
     */
    public String toString()
    {
      return name;
    }

    /**
     * Return an array of HTML tags, declared in HTML.Tag class.
     * WARNING: This method expects that the Tags are the only
     * public fields declared in the Tag class.
     */
    static Tag[] getAllTags()
    {
      Field[] f = Tag.class.getFields();
      Field x;

      // The syntetic tags are not included.
      Tag[] tags = new Tag[ f.length - TOTAL_SYNTHETIC_TAGS ];
      int p = 0;
      Tag t;

      for (int i = 0; i < f.length; i++)
        {
          x = f [ i ];

          if ((x.getModifiers() & Modifier.STATIC) != 0)
            {
              if (x.getType().equals(Tag.class))
                {
                  try
                    {
                      t = (Tag) x.get(null);

                      if (!t.isSyntetic())
                        {
                          tags [ p++ ] = t;
                        }
                    }
                  catch (IllegalAccessException ex)
                    {
                      unexpected(ex);
                    }
                  catch (IllegalArgumentException ex)
                    {
                      unexpected(ex);
                    }
                }
            }
        }

      return tags;
    }

    /**
     * Returns true for tags, generated by the html reader
     * (COMMENT, CONTENT and IMPLIED).
     */
    boolean isSyntetic()
    {
      return (flags & SYNTHETIC) != 0;
    }

    private static void unexpected(Exception ex)
                            throws Error
    {
      throw new Error("This should never happen, report a bug", ex);
    }
  }

  /**
   * Represents an unknown HTML tag.
   * @author Mark Wielaard ([e-mail])
   */
  public static class UnknownTag
    extends Tag
    implements Serializable
  {
    private static final long serialVersionUID = -1534369342247250625L;

    /**
     * Creates a new UnknownTag with the specified name
     * @param name The tag name.
     *
     */
    public UnknownTag(String name)
    {
      super(name);
    }
  }

  /**
   * This value is returned for attributes without value that have no
   * default value defined in the DTD.
   */
  public static final String NULL_ATTRIBUTE_VALUE = "#DEFAULT";

  /* Package level html tag flags */
  static final int BREAKS = 1;
  static final int BLOCK = 2;
  static final int PREFORMATTED = 4;
  static final int SYNTHETIC = 8;
  private static Map tagMap;
  private static Map attrMap;

  /**
   * The public constructor (does nothing). It it seldom required to have
   * an instance of this class, because all public fields and methods
   * are static.
   */
  public HTML()
  {
    // Nothing to do here.
  }

  /**
   * Returns the set of the recognized HTML attributes.
   */
  public static HTML.Attribute[] getAllAttributeKeys()
  {
    return Attribute.getAllAttributes();
  }

  /**
   * Returns the set of actual HTML tags that are recognized by
   * the default HTML reader. The returned array does not include the
   * COMMENT, CONTENT and IMPLIED tags.
   */
  public static HTML.Tag[] getAllTags()
  {
    return Tag.getAllTags();
  }

  /**
   * Returns an htl attribute constant for the given attribute name.
   * @param attName the attribute name, case insensitive
   */
  public static Attribute getAttributeKey(String attName)
  {
    if (attrMap == null)
      {
        // Create the map on demand.
        attrMap = new TreeMap();

        Attribute[] attrs = getAllAttributeKeys();

        for (int i = 0; i < attrs.length; i++)
          {
            attrMap.put(attrs [ i ].toString(), attrs [ i ]);
          }
      }

    return (Attribute) attrMap.get(attName.toLowerCase());
  }

  /**
   * Searches the value of given attribute in the provided set.
   * If the value is found (String type expected), tries to parse it as
   * an integer value. If succeded, returns the obtained integer value.
   *
   * For example:<p><code>
   * SimpleAttributeSet ase = new SimpleAttributeSet();
   * ase.addAttribute(HTML.getAttributeKey("size"),"222");
   * System.out.println(
   *  HTML.getIntegerAttributeValue
   *     (ase, HTML.getAttributeKey("size"), 333)); // prints "222"
   * System.out.println(
   *  HTML.getIntegerAttributeValue
   *     (ase, HTML.getAttributeKey("width"), 333)); // prints "333".
   * </code></p>
   *
   *
   * @param set The attribute set to search in. If the set contains the
   * given attribute, it must by a type of String.
   * @param attribute The html attribute to search in
   * @param defaultValue The value that is returned if the attribute is not
   * found in the given set or if the NumberFormatException was thrown
   * during the parsing.
   */
  public static int getIntegerAttributeValue(AttributeSet set,
                                             HTML.Attribute attribute,
                                             int defaultValue
                                            )
  {
    Object v = set.getAttribute(attribute);

    if (v == null)
      {
        return defaultValue;
      }

    try
      {
        return Integer.parseInt(v.toString().trim());
      }
    catch (Exception ex)
      {
        return defaultValue;
      }
  }

  /**
   * Returns a HTML tag constant for the given HTML attribute name.
   * If the tag is unknown, the null is returned.
   * @param tagName the tag name, case insensitive
   */
  public static Tag getTag(String tagName)
  {
    if (tagMap == null)
      {
        // Create the mao on demand.
        tagMap = new TreeMap();

        Tag[] tags = getAllTags();

        for (int i = 0; i < tags.length; i++)
          {
            tagMap.put(tags [ i ].toString(), tags [ i ]);
          }
      }

    return (Tag) tagMap.get(tagName.toLowerCase());
  }
}