How to: Compress Files

Use the System.IO.Compression.GZipStream class to compress and decompress data. You can also use the System.IO.Compression.DeflateStream class, which uses the same compression algorithm; however, compressed GZipStream objects written to a file that has an extension of .gz can be decompressed using many common compression tools.

This example shows how to compress and decompress a directory of files by using the GZipStream class.


Imports System.IO
Imports System.IO.Compression
Module Module1

    Sub Main()
        ' Path to directory of files to compress.
        Dim dirpath As String = "c:\users\public\reports"

        Dim di As DirectoryInfo = New DirectoryInfo(dirpath)


        ' Compress the directory's files.
        For Each fi As FileInfo In di.GetFiles()
            Compress(fi)
        Next

        ' Decompress all *.gz files in the directory.
        For Each fi As FileInfo In di.GetFiles("*.gz")
            Decompress(fi)
        Next

    End Sub

    ' Method to compress.
    Private Sub Compress(ByVal fi As FileInfo)
        ' Get the stream of the source file.
        Using inFile As FileStream = fi.OpenRead()
            ' Compressing:
            ' Prevent compressing hidden and already compressed files.

            If (File.GetAttributes(fi.FullName) And FileAttributes.Hidden) _
                <> FileAttributes.Hidden And fi.Extension <> ".gz" Then
                ' Create the compressed file.
                Using outFile As FileStream = File.Create(fi.FullName + ".gz")
                    Using Compress As GZipStream = _
                    	New GZipStream(outFile, CompressionMode.Compress)
                    	
                        ' Copy the source file into the compression stream.
                        inFile.CopyTo(Compress)

                        Console.WriteLine("Compressed {0} from {1} to {2} bytes.", _
                                          fi.Name, fi.Length.ToString(), outFile.Length.ToString())

                    End Using
                End Using
            End If
        End Using
    End Sub

    ' Method to decompress.
    Private Sub Decompress(ByVal fi As FileInfo)
        ' Get the stream of the source file.
        Using inFile As FileStream = fi.OpenRead()
            ' Get orignial file extension, for example "doc" from report.doc.gz.
            Dim curFile As String = fi.FullName
            Dim origName = curFile.Remove(curFile.Length - fi.Extension.Length)

            ' Create the decompressed file.
            Using outFile As FileStream = File.Create(origName)
                Using Decompress As GZipStream = New GZipStream(inFile, _
                	CompressionMode.Decompress)
            		
  						' Copy the decompression stream 
                        ' into the output file.
            		    Decompress.CopyTo(outFile)

                    Console.WriteLine("Decompressed: {0}", fi.Name)

                End Using
            End Using
        End Using
    End Sub
End Module


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