SkipCommentReader.java

/*
 * Copyright (C) 2011 eXo Platform SAS.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.exoplatform.portal.resource;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;


/**
 *
 * A subclass of BufferedReader which skip the comment block
 *
 * @author <a href="hoang281283@gmail.com">Minh Hoang TO</a>
 * @date 6/27/11
 */
public class SkipCommentReader extends BufferedReader {

    private final StringBuilder pushbackCache;

    private static final int EOF = -1;

    private State cursorState;

    private CommentBlockHandler commentBlockHandler;

    /* The number of next comming characters that won't be skipped even if they are in a comment block */
    private int numberOfCommingEscapes;

    public SkipCommentReader(Reader reader) {
        this(reader, null);
    }

    public SkipCommentReader(Reader reader, CommentBlockHandler handler) {
        super(reader);
        pushbackCache = new StringBuilder();
        cursorState = State.ENCOUNTING_ORDINARY_CHARACTER;
        this.commentBlockHandler = handler;
    }

    /**
     * Recursive method that read a single character from underlying reader. Encountered comment block is escaped automatically.
     *
     * @return
     * @throws IOException
     */
    public int readSingleCharacter() throws IOException {
        int readingChar = readLikePushbackReader();
        if (readingChar == EOF) {
            return EOF;
        }

        if (numberOfCommingEscapes > 0) {
            numberOfCommingEscapes--;
            return readingChar;
        }

        switch (readingChar) {
            case '/':
                int nextCharToRead = read();
                if (nextCharToRead == '*') {
                    this.cursorState = SkipCommentReader.State.ENCOUNTING_COMMENT_BLOCK_OPENING_TAG;
                    advanceToEscapeCommentBlock();
                    return readSingleCharacter();
                } else {
                    this.cursorState = SkipCommentReader.State.ENCOUNTING_FORWARD_SLASH;
                    pushbackCache.append((char) nextCharToRead);
                    return '/';
                }

            case '*':
                if (this.cursorState == SkipCommentReader.State.ENCOUNTING_FORWARD_SLASH) {
                    this.cursorState = SkipCommentReader.State.ENCOUNTING_COMMENT_BLOCK_OPENING_TAG;
                    advanceToEscapeCommentBlock();
                    return readSingleCharacter();
                } else {
                    this.cursorState = SkipCommentReader.State.ENCOUNTING_ASTERIK;
                    return '*';
                }

            default:
                this.cursorState = SkipCommentReader.State.ENCOUNTING_ORDINARY_CHARACTER;
                return readingChar;
        }

    }

    /**
     * Read from the pushback cache first, then underlying reader
     */
    private int readLikePushbackReader() throws IOException {
        if (pushbackCache.length() > 0) {
            int readingChar = pushbackCache.charAt(0);
            pushbackCache.deleteCharAt(0);
            return readingChar;
        }
        return read();
    }

    /**
     * Advance in comment block until we reach a comment block closing tag
     */
    private void advanceToEscapeCommentBlock() throws IOException {
        if (cursorState != SkipCommentReader.State.ENCOUNTING_COMMENT_BLOCK_OPENING_TAG) {
            throw new IllegalStateException("This method should be invoked only if we are entering a comment block");
        }

        int readingChar = read();
        StringBuilder commentBlock = new StringBuilder("/*");

        LOOP: while (readingChar != EOF) {
            commentBlock.append((char) readingChar);
            if (readingChar == '/') {
                if (this.cursorState == SkipCommentReader.State.ENCOUNTING_ASTERIK) {
                    this.cursorState = SkipCommentReader.State.ENCOUNTING_COMMENT_BLOCK_CLOSING_TAG;
                    break LOOP; // We 've just escaped the comment block
                } else {
                    this.cursorState = SkipCommentReader.State.ENCOUNTING_FORWARD_SLASH;
                }
            } else {
                this.cursorState = (readingChar == '*') ? SkipCommentReader.State.ENCOUNTING_ASTERIK
                        : SkipCommentReader.State.ENCOUNTING_ORDINARY_CHARACTER;
            }
            readingChar = read();
        }

        if (commentBlockHandler != null) {
            commentBlockHandler.handle(commentBlock, this);
        }
    }

    @Override
    public String readLine() throws IOException {
        StringBuilder builder = new StringBuilder();
        int nextChar = readSingleCharacter();
        if (nextChar == EOF) {
            return null;
        }

        while (nextChar != EOF) {
            if (nextChar == '\n' || nextChar == '\r') {
                break;
            }
            builder.append((char) nextChar);
            nextChar = readSingleCharacter();
        }

        return builder.toString().trim();
    }

    /**
     * Used for JUnit tests
     *
     * @return
     */
    public State getCursorState() {
        return this.cursorState;
    }

    public void setCommentBlockHandler(CommentBlockHandler commentBlockHandler) {
        this.commentBlockHandler = commentBlockHandler;
    }

    public void setNumberOfCommingEscapes(int numberOfCommingEscapes) {
        this.numberOfCommingEscapes = numberOfCommingEscapes;
    }

    public void pushback(CharSequence sequence) {
        this.pushbackCache.append(sequence);
    }

    public enum State {
        ENCOUNTING_FORWARD_SLASH,

        ENCOUNTING_ASTERIK,

        ENCOUNTING_COMMENT_BLOCK_OPENING_TAG,

        ENCOUNTING_COMMENT_BLOCK_CLOSING_TAG,

        ENCOUNTING_ORDINARY_CHARACTER
    }
}