compressedinputstream.java

我费了好大劲才找到的一款非常全的OA办公自动化软件源码

/*
 Copyright (C) 2002-2004 MySQL AB

 This program is free software; you can redistribute it and/or modify
 it under the terms of version 2 of the GNU General Public License as
 published by the Free Software Foundation.
 

 There are special exceptions to the terms and conditions of the GPL 
 as it is applied to this software. View the full text of the 
 exception exception in file EXCEPTIONS-CONNECTOR-J in the directory of this 
 software distribution.

 This program 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 General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*/
package com.mysql.jdbc;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

import java.util.zip.DataFormatException;
import java.util.zip.Inflater;


/**
* Used to de-compress packets from the MySQL server when protocol-level
* compression is turned on.
* 
* @author Mark Matthews
* 
* @version $Id: CompressedInputStream.java,v 1.1.4.5 2004/08/09 22:15:11 mmatthew Exp $
*/
class CompressedInputStream extends InputStream {

 /** The ZIP inflater used to un-compress packets */
 private Inflater inflater;

 /** The stream we are reading from the server */
 private InputStream in;

 /** The packet data after it has been un-compressed */
 private byte[] buffer;

 /** The position we are reading from */
 private int pos = 0;
 
 /**
  * The buffer to read packet headers into
  */
 private byte[] packetHeaderBuffer = new byte[7];

 /**
  * Creates a new CompressedInputStream that reads the given stream from the
  * server.
  *
  * @param conn DOCUMENT ME!
  * @param streamFromServer
  */
 public CompressedInputStream(InputStream streamFromServer) {
     this.in = streamFromServer;
     this.inflater = new Inflater();
 }

 /**
  * @see java.io.InputStream#available()
  */
 public int available() throws IOException {
     if (this.buffer == null) {
         return this.in.available();
     }

     return this.buffer.length - this.pos + this.in.available();
 }

 /**
  * @see java.io.InputStream#close()
  */
 public void close() throws IOException {
     this.in.close();
     this.buffer = null;
     this.inflater = null;
 }

 /**
  * @see java.io.InputStream#read()
  */
 public int read() throws IOException {
     try {
         getNextPacketIfRequired(1);
     } catch (IOException ioEx) {
         return -1;
     }

     return this.buffer[this.pos++] & 0xff;
 }

 /**
  * @see java.io.InputStream#read(byte, int, int)
  */
 public int read(byte[] b, int off, int len) throws IOException {
     if (b == null) {
         throw new NullPointerException();
     } else if ((off < 0) || (off > b.length) || (len < 0)
             || ((off + len) > b.length) || ((off + len) < 0)) {
         throw new IndexOutOfBoundsException();
     }

     if (len <= 0) {
         return 0;
     }

     try {
         getNextPacketIfRequired(len);
     } catch (IOException ioEx) {
         return -1;
     }

     System.arraycopy(this.buffer, this.pos, b, off, len);
     this.pos += len;

     return len;
 }

 /**
  * @see java.io.InputStream#read(byte)
  */
 public int read(byte[] b) throws IOException {
     return read(b, 0, b.length);
 }

 /**
  * @see java.io.InputStream#skip(long)
  */
 public long skip(long n) throws IOException {
     long count = 0;

     for (long i = 0; i < n; i++) {
         int bytesRead = read();

         if (bytesRead == -1) {
             break;
         }

         count++;
     }

     return count;
 }

 /**
  * Retrieves and un-compressed (if necessary) the next packet from the
  * server.
  *
  * @throws IOException if an I/O error occurs
  */
 private void getNextPacketFromServer() throws IOException {
     byte[] uncompressedData = null;

     int lengthRead = readFully(this.packetHeaderBuffer, 0,
             7);

     if (lengthRead < 7) {
         throw new IOException("Unexpected end of input stream");
     }

     int compressedPacketLength = ((int) (this.packetHeaderBuffer[0] & 0xff))
         + (((int) (this.packetHeaderBuffer[1] & 0xff)) << 8)
         + (((int) (this.packetHeaderBuffer[2] & 0xff)) << 16);
      
     int uncompressedLength = ((int) (this.packetHeaderBuffer[4] & 0xff))
         + (((int) (this.packetHeaderBuffer[5] & 0xff)) << 8)
         + (((int) (this.packetHeaderBuffer[6] & 0xff)) << 16);
     
     if (uncompressedLength > 0) {
         uncompressedData = new byte[uncompressedLength];

         byte[] compressedBuffer = new byte[compressedPacketLength];

         readFully(compressedBuffer, 0, compressedPacketLength);

         try {
             this.inflater.reset();
         } catch (NullPointerException npe) {
             this.inflater = new Inflater();
         }

         this.inflater.setInput(compressedBuffer);

         try {
             this.inflater.inflate(uncompressedData);
         } catch (DataFormatException dfe) {
             throw new IOException(
                 "Error while uncompressing packet from server.");
         }

         this.inflater.end();
     } else {
        
         //	
         //	Read data, note this this code is reached when using
         //  compressed packets that have not been compressed, as well
         //
         uncompressedData = new byte[compressedPacketLength];
         readFully(uncompressedData, 0, compressedPacketLength);
     }

     if ((this.buffer != null) && (this.pos < this.buffer.length)) {
         
         int remaining = buffer.length - this.pos;
         byte[] newBuffer = new byte[remaining + uncompressedData.length];

         int newIndex = 0;

         for (int i = this.pos; i < this.buffer.length; i++)
             newBuffer[newIndex++] = this.buffer[i];

         System.arraycopy(uncompressedData, 0, newBuffer, newIndex,
             uncompressedData.length);

         uncompressedData = newBuffer; 
     }
     
     this.pos = 0;
     this.buffer = uncompressedData;

     return;
 }

 /**
  * Determines if another packet needs to be read from the server to be able
  * to read numBytes from the stream.
  *
  * @param numBytes the number of bytes to be read
  *
  * @throws IOException if an I/O error occors.
  */
 private void getNextPacketIfRequired(int numBytes)
     throws IOException {
     if ((this.buffer == null)
             || ((this.pos + numBytes) > this.buffer.length)) {
         getNextPacketFromServer();
     }
 }

 private final int readFully(byte[] b, int off, int len)
     throws IOException {
     if (len < 0) {
         throw new IndexOutOfBoundsException();
     }

     int n = 0;

     while (n < len) {
         int count = this.in.read(b, off + n, len - n);

         if (count < 0) {
             throw new EOFException();
         }

         n += count;
     }

     return n;
 }
}