java中关于html的转换

请看下面这个例子
  public static String escapeHTMLTags( String input ) {
        // Check if the string is null or zero length -- if so, return what was sent in.
        if( input == null || input.length() == 0 ) {
            return input;
        }
        // Use a StringBuffer in lieu of String concatenation -- it is much more efficient this way.
        StringBuffer buf = new StringBuffer();
        char ch = ' ';
        for( int i=0; i<input.length(); i++ ) {
            ch = input.charAt(i);
            if( ch == '<' ) {
                buf.append( "<" );
            }
            else if( ch == '>' ) {
                buf.append( ">" );
            }
            else {
                buf.append( ch );
            }
        }
        return buf.toString();
    }