fromnetasciiinputstream.java

来自「apache推出的net包」· Java 代码 · 共 200 行

/*
 * Copyright 2001-2005 The Apache Software Foundation
 *
 * Licensed 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.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;

/***
 * This class wraps an input stream, replacing all occurrences
 * of <CR><LF> (carriage return followed by a linefeed),
 * which is the NETASCII standard for representing a newline, with the
 * local line separator representation.  You would use this class to
 * implement ASCII file transfers requiring conversion from NETASCII.
 * <p>
 * <p>
 * @author Daniel F. Savarese
 ***/

public final class FromNetASCIIInputStream extends PushbackInputStream
{
    static final boolean _noConversionRequired;
    static final String _lineSeparator;
    static final byte[] _lineSeparatorBytes;

    static {
        _lineSeparator = System.getProperty("line.separator");
        _noConversionRequired = _lineSeparator.equals("\r\n");
        _lineSeparatorBytes = _lineSeparator.getBytes();
    }

    private int __length = 0;

    /***
     * Returns true if the NetASCII line separator differs from the system
     * line separator, false if they are the same.  This method is useful
     * to determine whether or not you need to instantiate a
     * FromNetASCIIInputStream object.
     * <p>
     * @return True if the NETASCII line separator differs from the local
     *   system line separator, false if they are the same.
     ***/
    public static final boolean isConversionRequired()
    {
        return !_noConversionRequired;
    }

    /***
     * Creates a FromNetASCIIInputStream instance that wraps an existing
     * InputStream.
     ***/
    public FromNetASCIIInputStream(InputStream input)
    {
        super(input, _lineSeparatorBytes.length + 1);
    }


    private int __read() throws IOException
    {
        int ch;

        ch = super.read();

        if (ch == '\r')
        {
            ch = super.read();
            if (ch == '\n')
            {
                unread(_lineSeparatorBytes);
                ch = super.read();
                // This is a kluge for read(byte[], ...) to read the right amount
                --__length;
            }
            else
            {
                if (ch != -1)
                    unread(ch);
                return '\r';
            }
        }

        return ch;
    }


    /***
     * Reads and returns the next byte in the stream.  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 in order
     * to convert NETASCII line separators to the local line separator format.
     * This is transparent to the programmer and is only mentioned for
     * completeness.
     * <p>
     * @return The next character in the stream. Returns -1 if the end of the
     *          stream has been reached.
     * @exception IOException If an error occurs while reading the underlying
     *            stream.
     ***/
    public int read() throws IOException
    {
        if (_noConversionRequired)
            return super.read();

        return __read();
    }


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


    /***
     * Reads the next number of bytes from the stream into an array and returns
     * the number of bytes 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.
     * <p>
     * @param buffer The byte array in which to store the data.
     * @param offset  The offset into the array at which to start storing data.
     * @param length   The number of bytes to read.
     * @return The number of bytes read. Returns -1 if the
     *          end of the stream has been reached.
     * @exception IOException If an error occurs while reading the underlying
     *            stream.
     ***/
    public int read(byte buffer[], int offset, int length) throws IOException
    {
        int ch, off;

        if (length < 1)
            return 0;

        ch = available();

        __length = (length > ch ? ch : length);

        // If nothing is available, block to read only one character
        if (__length < 1)
            __length = 1;

        if (_noConversionRequired)
            return super.read(buffer, offset, __length);

        if ((ch = __read()) == -1)
            return -1;

        off = offset;

        do
        {
            buffer[offset++] = (byte)ch;
        }
        while (--__length > 0 && (ch = __read()) != -1);


        return (offset - off);
    }


    // PushbackInputStream in JDK 1.1.3 returns the wrong thing
    /***
     * Returns the number of bytes that can be read without blocking EXCEPT
     * when newline conversions have to be made somewhere within the
     * available block of bytes.  In other words, you really should not
     * rely on the value returned by this method if you are trying to avoid
     * blocking.
     ***/
    public int available() throws IOException
    {
        return (buf.length - pos) + in.available();
    }

}