ifheader.java

jsr170接口的java实现。是个apache的开源项目。

     */
    private IfHeaderList parseUntagged(StringReader reader) {
        IfHeaderList list = new IfHeaderList();
        try {
            while (true) {
                // read next non-whitespace
                reader.mark(1);
                int c = readWhiteSpace(reader);
                if (c < 0) {
                    // end of input, no more IfLists
                    break;

                } else if (c == '(') {
                    // start of an IfList, parse
                    list.add(parseIfList(reader));

                } else if (c == '<') {
                    // start of a tag, return current list
                    reader.reset();
                    break;

                } else {
                    // unexpected character
                    // catchup to end of input or start of an IfList
                    logIllegalState("Untagged", c, "(", reader);
                }
            }
        } catch (IOException ioe) {
            log.error("parseUntagged: Problem parsing If header: "+ioe.toString());
        }
        return list;
    }

    /**
     * Parses an <em>IfList</em> in the <em>If</em> header. This method
     * implements the <em>Tagged</em> production given in the class comment :
     * <pre>
         IfList = { [ "Not" ] ( ("<" Word ">" ) | ( "[" Word "]" ) ) } .
     * </pre>
     *
     * @param reader The <code>StringReader</code> to read from for parsing
     *
     * @return The {@link IfList} for the input <em>IfList</em>.
     *
     * @throws IOException if a problem occurrs during reading.
     */
    private IfList parseIfList(StringReader reader) throws IOException {
        IfList res = new IfList();
        boolean positive = true;
        String word;

        ReadLoop:
        while (true) {
            int nextChar = readWhiteSpace(reader);
            switch (nextChar) {
                case 'N':
                case 'n':
                    // read not

                    // check whether o or O
                    int not = reader.read();
                    if (not != 'o' && not != 'O') {
                        logIllegalState("IfList-Not", not, "o", null);
                        break;
                    }

                    // check whether t or T
                    not = reader.read();
                    if (not !='t' || not != 'T') {
                        logIllegalState("IfList-Not", not, "t", null);
                        break;
                    }

                    // read Not ok
                    positive = false;
                    break;

                case '<':
                    // state token
                    word = readWord(reader, '>');
                    if (word != null) {
                        res.add(new IfListEntryToken(word, positive));
                        // also add the token to the list of all tokens
                        if (positive) {
                            allTokens.add(word);
                        } else {
                            allNotTokens.add(word);
                        }
                        positive = true;
                    }
                    break;

                case '[':
                    // etag
                    word = readWord(reader, ']');
                    if (word != null) {
                        res.add(new IfListEntryEtag(word, positive));
                        positive = true;
                    }
                    break;

                case ')':
                    // correct end of list, end the loop
                    log.debug("parseIfList: End of If list, terminating loop");
                    break ReadLoop;

                default:
                    logIllegalState("IfList", nextChar, "nN<[)", reader);

                    // abort loop if EOF
                    if (nextChar < 0) {
                        break ReadLoop;
                    }

                    break;
            }
        }

        // return the current list anyway
        return res;
    }

    /**
     * Returns the first non-whitespace character from the reader or -1 if
     * the end of the reader is encountered.
     *
     * @param reader The <code>Reader</code> to read from
     *
     * @return The first non-whitespace character or -1 in case of EOF.
     *
     * @throws IOException if a problem occurrs during reading.
     */
    private int readWhiteSpace(Reader reader) throws IOException {
        int c = reader.read();
        while (c >= 0 && Character.isWhitespace((char) c)) {
             c = reader.read();
        }
        return c;
    }

    /**
     * Reads from the input until the end character is encountered and returns
     * the string upto but not including this end character. If the end of input
     * is reached before reading the end character <code>null</code> is
     * returned.
     * <p>
     * Note that this method does not support any escaping.
     *
     * @param reader The <code>Reader</code> to read from
     * @param end The ending character limitting the word.
     *
     * @return The string read upto but not including the ending character or
     *      <code>null</code> if the end of input is reached before the ending
     *      character has been read.
     *
     * @throws IOException if a problem occurrs during reading.
     */
    private String readWord(Reader reader, char end) throws IOException {
        StringBuffer buf = new StringBuffer();

        // read the word value
        int c = reader.read();
        for (; c >= 0 && c != end; c=reader.read()) {
            buf.append((char) c);
        }

        // check whether we succeeded
        if (c < 0) {
            log.error("readWord: Unexpected end of input reading word");
            return null;
        }

        // build the string and return it
        return buf.toString();
    }

    /**
     * Logs an unexpected character with the corresponding state and list of
     * expected characters. If the reader parameter is not null, characters
     * are read until either the end of the input is reached or any of the
     * characters in the expChar string is read.
     *
     * @param state The name of the current parse state. This method logs this
     *      name in the message. The intended value would probably be the
     *      name of the EBNF production during which the error occurrs.
     * @param effChar The effective character read.
     * @param expChar The list of characters acceptable in the current state.
     * @param reader The reader to be caught up to any of the expected
     *      characters. If <code>null</code> the input is not caught up to
     *      any of the expected characters (of course ;-).
     */
    private void logIllegalState(String state, int effChar, String expChar,
                                 StringReader reader) {

        // format the effective character to be logged
        String effString = (effChar < 0) ? "<EOF>" : String.valueOf((char) effChar);

        // log the error
        log.error("logIllegalState: Unexpected character '"+effString+" in state "+state+", expected any of "+expChar);

        // catch up if a reader is given
        if (reader != null && effChar >= 0) {
            try {
                log.debug("logIllegalState: Catch up to any of "+expChar);
                do {
                    reader.mark(1);
                    effChar = reader.read();
                } while (effChar >= 0 && expChar.indexOf(effChar) < 0);
                if (effChar >= 0) {
                    reader.reset();
                }
            } catch (IOException ioe) {
                log.error("logIllegalState: IO Problem catching up to any of "+expChar);
            }
        }
    }

    //---------- internal If header structure ----------------------------------

    /**
     * The <code>IfListEntry</code> abstract class is the base class for
     * entries in an <em>IfList</em> production. This abstract base class
     * provides common functionality to both types of entries, namely tokens
     * enclosed in angle brackets (<code>&lt; &gt;</code>) and etags enclosed
     * in square brackets (<code>[ ]</code>).
     */
    private static abstract class IfListEntry {

        /**
         * The entry string value - the semantics of this value depends on the
         * implementing class.
         */
        protected final String value;

        /** Flag to indicate, whether this is a positive match or not */
        protected final boolean positive;

        /** The cached result of the {@link #toString} method. */
        protected String stringValue;

        /**
         * Sets up the final fields of this abstract class. The meaning of
         * value parameter depends solely on the implementing class. From the
         * point of view of this abstract class, it is simply a string value.
         *
         * @param value The string value of this instance
         * @param positive <code>true</code> if matches are positive
         */
        protected IfListEntry(String value, boolean positive) {
            this.value = value;
            this.positive = positive;
        }

        /**
         * Matches the value from the parameter to the internal string value.
         * If the parameter and the {@link #value} field match, the method
         * returns <code>true</code> for positive matches and <code>false</code>
         * for negative matches.
         * <p>
         * This helper method can be called by implementations to evaluate the
         * concrete match on the correct value parameter. See
         * {@link #match(String, String)} for the external API method.
         *
         * @param value The string value to compare to the {@link #value}
         *      field.
         *
         * @return <code>true</code> if the value parameter and the
         *      {@link #value} field match and the {@link #positive} field is
         *      <code>true</code> or if the values do not match and the
         *      {@link #positive} field is <code>false</code>.
         */
        protected boolean match(String value) {
            return positive == this.value.equals(value);
        }

        /**
         * Matches the entry's value to the the token or etag. Depending on the
         * concrete implementation, only one of the parameters may be evaluated
         * while the other may be ignored.
         * <p>
         * Implementing METHODS may call the helper method {@link #match(String)}
         * for the actual matching.
         *
         * @param token The token value to compare
         * @param etag The etag value to compare
         *
         * @return <code>true</code> if the token/etag matches the <em>IfList</em>
         *      entry.
         */
        public abstract boolean match(String token, String etag);

        /**
         * Returns a short type name for the implementation. This method is
         * used by the {@link #toString} method to build the string representation
         * if the instance.
         *
         * @return The type name of the implementation.
         */
        protected abstract String getType();

	/**
	 * Returns the value of this entry.
	 *
	 * @return the value