.NET中利用GZipStream实现压缩与解压缩

.NET中为我们提供了一些用于压缩和解压缩的类，其中GZipStream是比较常用的之一。通过GZipStream的构造函数我们知道，可以通过向GZipStream的构造函数传入CompressonMode参数指定生成的该实例是用于压缩(Compress)还是解压缩(Decompress)。

1 public GZipStream(Stream stream, CompressionMode mode);

该构造函数表明我们还需要指定一个流对象作为输入参数。注意这里的stream所对应的一定是一个和压缩有关的流。也就是说，如果我们指定CompressionMode为Decompress的话，那么stream对象应该为一个输入流(input stream)，该输入流的格式已经压缩过的，我们通过GZipStream的实例将压缩数据(input stream)读取出来后生成的数据就为解压缩过后的数据了。如果我们指定CompressionMode为Compression的话，那么stream对应的流一定是一个将要压缩的输出流 (output stream)，我们通过GZipStream的实例将普通流写入输出流中，输出流中的数据就为压缩后的数据了。

例1： 现在有一个已经压缩好的文件FileA.txt.gz，我们现在要做的工作是将该文件解压缩为FileB.txt。具体步骤通过下面的代码演示:

 1             //input file (already compressed)
 2             string fileA = "FileA.txt.gz";
 3             //output file (need to decompress FileA then write to fileB)
 4             string fileB = "FileB.txt";
 5
 6             //byte array buffer
 7             byte[] buffer = new byte[BUFFER_SIZE];
 8             int bytesReaded = 0;
 9
10
11             //input file stream
12             Stream fileAStream = new FileStream(fileA, FileMode.Open, FileAccess.Read);
13             //output file stream
14             Stream fileBStream = new FileStream(fileB, FileMode.Create, FileAccess.Write);
15             //use fileAStream as inputStream
16             GZipStream gzipStream = new GZipStream(fileAStream, CompressionMode.Decompress);
17
18             do
19             {
20                 //read from inputStream, data in buffer is decopressed
21                 bytesReaded = gzipStream.Read(buffer, 0, BUFFER_SIZE);
22                 //writed decompressed data into output stream
23                 fileBStream.Write(buffer, 0, bytesReaded);
24             } while (bytesReaded > 0);
25
26             //close related streams.
27             fileAStream.Close();
28             gzipStream.Close();
29             fileBStream.Close(); 

例2:现在我们已经将FileA.txt.gz文件解压缩为FileB.txt文件了。接下来的实例演示了如果将FileB.txt压缩为FileC.txt.gz

 1             //input file (flat file)
 2             string fileB = "FileB.txt";
 3             //output file (need to be compressed from FileB then write to FileC)
 4             string fileC = "FileC.txt.gz";
 5
 6             //byte array buffer
 7             byte[] buffer = new byte[BUFFER_SIZE];
 8             int bytesReaded = 0;
 9
10             //input stream
11             Stream fileBStream = new FileStream(fileB, FileMode.Open, FileAccess.Read);
12             //output stream
13             Stream fileCStream = new FileStream(fileC, FileMode.Create, FileAccess.Write);
14             //specify fileCStream as target stream, we need to compress fileB then write to fileC, so specify CompressionMode to Compress
15             GZipStream gzipStream = new GZipStream(fileCStream, CompressionMode.Compress);
16
17             do
18             {
19                 //read from fileBStream
20                 bytesReaded = fileBStream.Read(buffer, 0, BUFFER_SIZE);
21                 //write to fileCStream
22                 gzipStream.Write(buffer, 0, bytesReaded);
23             } while (bytesReaded > 0);
24             //close related streams.
25             fileBStream.Close();
26             gzipStream.Close();
27             fileCStream.Close();