.Net Framework 2.0中的Compression功能
以前做项目的时候,需要提供文件压缩功能。当时是使用了一个开源的类库,名为ZipLib,使用起来还是很方便的。我还在自己的英文博客上post了一篇文章《ZipLib Works Well! 》也许是看到了这个功能的必要性,在.Net 2.0中,微软在System.IO中新增了System.IO.Compression命名空间,提供了压缩功能的相关类GZipStream。
这个类的使用与一般的文件流使用差不多。我没有分析其内部实现,但猜测应该还是采用Decorator模式对Stream进行了装饰,从中应用了Compression算法。它通过Write()方法,将buffer里面的内容写到另一个文件流中,例如源文件为sourceFile,压缩后的文件为targetFile,则方法为:
byte[] buffer = null;
FileStream sourceStream = null;
FileStream targetStream = null;
GZipStream compressedStream = null;
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sourceStream = new FileStream(sourceFile,FileMode.Open,FileAccess.Read,FileShare.Read);
buffer = new byte[sourceStream.Length];
sourceStream.Read(buffer,0,buffer.Length);
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targetStream = new FileStream(targetFile,FileMode.OpenOrCreate,FileAccess.Write);
//将CompressedStream指向targetStream;
compressedStream = new GZipStream(targetStream,CompressionMode.Compress,true);
compressStream.Write(buffer,0,buffer.Length);![](/Images/OutliningIndicators/None.gif)
在使用GZipStream时,需要添加引用:
using System.IO;
using System.IO.Compression;
解压缩与前面的方法差不多,仍然使用GZipStream文件流:
// Read in the compressed source stream
sourceStream = new FileStream ( sourceFile, FileMode.Open );
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// Create a compression stream pointing to the destiantion stream
decompressedStream = new GZipStream ( sourceStream, CompressionMode.Decompress, true );
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// Read the footer to determine the length of the destiantion file
quartetBuffer = new byte[4];
int position = (int)sourceStream.Length - 4;
sourceStream.Position = position;
sourceStream.Read ( quartetBuffer, 0, 4 );
sourceStream.Position = 0;
int checkLength = BitConverter.ToInt32 ( quartetBuffer, 0 );
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byte[] buffer = new byte[checkLength + 100];
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int offset = 0;
int total = 0;
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// Read the compressed data into the buffer
while ( true )
{
int bytesRead = decompressedStream.Read ( buffer, offset, 100 );
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if ( bytesRead == 0 )
break;
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offset += bytesRead;
total += bytesRead;
}
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// Now write everything to the destination file
destinationStream = new FileStream ( destinationFile, FileMode.Create );
destinationStream.Write ( buffer, 0, total );
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// and flush everyhting to clean out the buffer
destinationStream.Flush ( );
.Net 2.0中除了提供GZipStream外,还提供了DeflateStream类,它仍然具有压缩的功能,只是采用的压缩算法不同而已。
using System;
using System.IO;
using System.IO.Compression;
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public class DeflateTest
{
public static int ReadAllBytesFromStream(Stream stream, byte[] buffer)
{
// Use this method is used to read all bytes from a stream.
int offset = 0;
int totalCount = 0;
while (true)
{
int bytesRead = stream.Read(buffer, offset, 100);
if ( bytesRead == 0)
{
break;
}
offset += bytesRead;
totalCount += bytesRead;
}
return totalCount;
}
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public static bool CompareData(byte[] buf1, int len1, byte[] buf2, int len2)
{
// Use this method to compare data from two different buffers.
if (len1 != len2)
{
Console.WriteLine("Number of bytes in two buffer are different {0}:{1}", len1, len2);
return false;
}
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for ( int i= 0; i< len1; i++)
{
if ( buf1[i] != buf2[i])
{
Console.WriteLine("byte {0} is different {1}|{2}", i, buf1[i], buf2[i]);
return false;
}
}
Console.WriteLine("All bytes compare.");
return true;
}
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public static void DeflateCompressDecompress(string filename)
{
Console.WriteLine("Test compression and decompression on file {0}", filename);
FileStream infile;
try
{
// Open the file as a FileStream object.
infile = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read);
byte[] buffer = new byte[infile.Length];
// Read the file to ensure it is readable.
int count = infile.Read(buffer, 0, buffer.Length);
if ( count != buffer.Length)
{
infile.Close();
Console.WriteLine("Test Failed: Unable to read data from file");
return;
}
infile.Close();
MemoryStream ms = new MemoryStream();
// Use the newly created memory stream for the compressed data.
DeflateStream compressedzipStream = new DeflateStream(ms , CompressionMode.Compress, true);
Console.WriteLine("Compression");
compressedzipStream.Write(buffer, 0, buffer.Length);
// Close the stream.
compressedzipStream.Close();
Console.WriteLine("Original size: {0}, Compressed size: {1}", buffer.Length, ms.Length);
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// Reset the memory stream position to begin decompression.
ms.Position = 0;
DeflateStream zipStream = new DeflateStream(ms, CompressionMode.Decompress);
Console.WriteLine("Decompression");
byte[] decompressedBuffer = new byte[buffer.Length + 100];
// Use the ReadAllBytesFromStream to read the stream.
int totalCount = DeflateTest.ReadAllBytesFromStream(zipStream, decompressedBuffer);
Console.WriteLine("Decompressed {0} bytes", totalCount);
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if( !DeflateTest.CompareData(buffer, buffer.Length, decompressedBuffer, totalCount) )
{
Console.WriteLine("Error. The two buffers did not compare.");
}
zipStream.Close();
} // end try
catch (InvalidDataException)
{
Console.WriteLine("Error: The file being read contains invalid data.");
}
catch (FileNotFoundException)
{
Console.WriteLine("Error:The file specified was not found.");
}
catch (ArgumentException)
{
Console.WriteLine("Error: path is a zero-length string, contains only white space, or contains one or more invalid characters");
}
catch (PathTooLongException)
{
Console.WriteLine("Error: The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.");
}
catch (DirectoryNotFoundException)
{
Console.WriteLine("Error: The specified path is invalid, such as being on an unmapped drive.");
}
catch (IOException)
{
Console.WriteLine("Error: An I/O error occurred while opening the file.");
}
catch (UnauthorizedAccessException)
{
Console.WriteLine("Error: path specified a file that is read-only, the path is a directory, or caller does not have the required permissions.");
}
catch (IndexOutOfRangeException)
{
Console.WriteLine("Error: You must provide parameters for MyGZIP.");
}
}
public static void Main(string[] args)
{
string usageText = "Usage: DeflateTest <inputfilename>";
//If no file name is specified, write usage text.
if (args.Length == 0)
{
Console.WriteLine(usageText);
}
else
{
if (File.Exists(args[0]))
DeflateCompressDecompress(args[0]);
}
}
}
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微软在加入GZipSream和DeflateStream后,使得.Net对文件流的支持更加丰富。我们也可以直接利用.Net Framework 2.0写出自己的压缩程序了。
本文的代码部分来自Visual Studio 2005 101Sample C#.
这个类的使用与一般的文件流使用差不多。我没有分析其内部实现,但猜测应该还是采用Decorator模式对Stream进行了装饰,从中应用了Compression算法。它通过Write()方法,将buffer里面的内容写到另一个文件流中,例如源文件为sourceFile,压缩后的文件为targetFile,则方法为:
![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
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![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
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在使用GZipStream时,需要添加引用:
![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
解压缩与前面的方法差不多,仍然使用GZipStream文件流:
![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
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.Net 2.0中除了提供GZipStream外,还提供了DeflateStream类,它仍然具有压缩的功能,只是采用的压缩算法不同而已。
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微软在加入GZipSream和DeflateStream后,使得.Net对文件流的支持更加丰富。我们也可以直接利用.Net Framework 2.0写出自己的压缩程序了。
本文的代码部分来自Visual Studio 2005 101Sample C#.