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Commons Net example source code file (DotTerminatedMessageReader.java)

This example Commons Net source code file (DotTerminatedMessageReader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Net tags/keywords

cr, cr, dot, dot, dotterminatedmessagereader, eof, have, io, ioexception, ioexception, lf, lf, override, string, stringbuilder

The Commons Net DotTerminatedMessageReader.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.net.io;

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

/**
 * DotTerminatedMessageReader is a class used to read messages from a
 * server that are terminated by a single dot followed by a
 * <CR><LF>
 * sequence and with double dots appearing at the begining of lines which
 * do not signal end of message yet start with a dot.  Various Internet
 * protocols such as NNTP and POP3 produce messages of this type.
 * <p>
 * This class handles stripping of the duplicate period at the beginning
 * of lines starting with a period, and ensures you cannot read past the end of the message.
 * <p>
 * Note: versions since 3.0 extend BufferedReader rather than Reader,
 * and no longer change the CRLF into the local EOL. Also only DOT CR LF
 * acts as EOF.
 * @version $Id: DotTerminatedMessageReader.java 1088720 2011-04-04 18:52:00Z dfs $
 */
public final class DotTerminatedMessageReader extends BufferedReader
{
    private static final char LF = '\n';
    private static final char CR = '\r';
    private static final int DOT = '.';

    private boolean atBeginning;
    private boolean eof;
    private boolean seenCR; // was last character CR?

    /**
     * Creates a DotTerminatedMessageReader that wraps an existing Reader
     * input source.
     * @param reader  The Reader input source containing the message.
     */
    public DotTerminatedMessageReader(Reader reader)
    {
        super(reader);
        // Assumes input is at start of message
        atBeginning = true;
        eof = false;
    }

    /**
     * Reads and returns the next character in the message.  If the end of the
     * message has been reached, returns -1.  Note that a call to this method
     * may result in multiple reads from the underlying input stream to decode
     * the message properly (removing doubled dots and so on).  All of
     * this is transparent to the programmer and is only mentioned for
     * completeness.
     * @return The next character in the message. Returns -1 if the end of the
     *          message has been reached.
     * @exception IOException If an error occurs while reading the underlying
     *            stream.
     */
    @Override
    public int read() throws IOException {
        synchronized (lock) {
            if (eof) {
                return -1; // Don't allow read past EOF
            }
            int chint = super.read();
            if (chint == -1) { // True EOF
                eof = true;
                return -1;
            }
            if (atBeginning) {
                atBeginning = false;
                if (chint == DOT) { // Have DOT
                    mark(2); // need to check for CR LF or DOT
                    chint = super.read();
                    if (chint == -1) { // Should not happen
                        // new Throwable("Trailing DOT").printStackTrace();
                        eof = true;
                        return DOT; // return the trailing DOT
                    }
                    if (chint == DOT) { // Have DOT DOT
                        // no need to reset as we want to lose the first DOT
                        return chint; // i.e. DOT
                    }
                    if (chint == CR) { // Have DOT CR
                        chint = super.read();
                        if (chint == -1) { // Still only DOT CR - should not happen
                            //new Throwable("Trailing DOT CR").printStackTrace();
                            reset(); // So CR is picked up next time
                            return DOT; // return the trailing DOT
                        }
                        if (chint == LF) { // DOT CR LF
                            atBeginning = true;
                            eof = true;
                            // Do we need to clear the mark somehow?
                            return -1;
                        }
                    }
                    // Should not happen - lone DOT at beginning
                    //new Throwable("Lone DOT followed by "+(char)chint).printStackTrace();
                    reset();
                    return DOT;
                } // have DOT
            } // atBeginning

            // Handle CRLF in normal flow
            if (seenCR) {
                seenCR = false;
                if (chint == LF) {
                    atBeginning = true;
                }
            }
            if (chint == CR) {
                seenCR = true;
            }
            return chint;
        }
    }


    /**
     * Reads the next characters from the message into an array and
     * returns the number of characters read.  Returns -1 if the end of the
     * message has been reached.
     * @param buffer  The character array in which to store the characters.
     * @return The number of characters read. Returns -1 if the
     *          end of the message has been reached.
     * @exception IOException If an error occurs in reading the underlying
     *            stream.
     */
    @Override
    public int read(char[] buffer) throws IOException
    {
        return read(buffer, 0, buffer.length);
    }

    /**
     * Reads the next characters from the message into an array and
     * returns the number of characters read.  Returns -1 if the end of the
     * message has been reached.  The characters are stored in the array
     * starting from the given offset and up to the length specified.
     * @param buffer  The character array in which to store the characters.
     * @param offset   The offset into the array at which to start storing
     *              characters.
     * @param length   The number of characters to read.
     * @return The number of characters read. Returns -1 if the
     *          end of the message has been reached.
     * @exception IOException If an error occurs in reading the underlying
     *            stream.
     */
    @Override
    public int read(char[] buffer, int offset, int length) throws IOException
    {
        int ch, off;
        synchronized (lock)
        {
            if (length < 1)
            {
                return 0;
            }
            if ((ch = read()) == -1)
            {
                return -1;
            }
            off = offset;

            do
            {
                buffer[offset++] = (char) ch;
            }
            while (--length > 0 && (ch = read()) != -1);

            return (offset - off);
        }
    }

    /**
     * Closes the message for reading.  This doesn't actually close the
     * underlying stream.  The underlying stream may still be used for
     * communicating with the server and therefore is not closed.
     * <p>
     * If the end of the message has not yet been reached, this method
     * will read the remainder of the message until it reaches the end,
     * so that the underlying stream may continue to be used properly
     * for communicating with the server.  If you do not fully read
     * a message, you MUST close it, otherwise your program will likely
     * hang or behave improperly.
     * @exception IOException  If an error occurs while reading the
     *            underlying stream.
     */
    @Override
    public void close() throws IOException
    {
        synchronized (lock)
        {
            if (!eof)
            {
                while (read() != -1)
                {
                    // read to EOF
                }
            }
            eof = true;
            atBeginning = false;
        }
    }

    /**
     * Read a line of text.
     * A line is considered to be terminated by carriage return followed immediately by a linefeed.
     * This contrasts with BufferedReader which also allows other combinations.
     * @since 3.0
     */
    @Override
    public String readLine() throws IOException {
        StringBuilder sb = new StringBuilder();
        int intch;
        synchronized(lock) { // make thread-safe (hopefully!)
            while((intch = read()) != -1)
            {
                if (intch == LF && atBeginning) {
                    return sb.substring(0, sb.length()-1);
                }
                sb.append((char) intch);
            }
        }
        String string = sb.toString();
        if (string.length() == 0) { // immediate EOF
            return null;
        }
        // Should not happen - EOF without CRLF
        //new Throwable(string).printStackTrace();
        return string;
    }
}

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