Professional ASP.NET 3.5 in C# and Visual Basic Part 122 docx

Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1170 Chapter 25: File I/O and Streams FileStream resources as Close does, it can be very useful if you are going to perform multiple write operations and do not want to release and then reacquire the resources for each write operation. As you can see, so far reading and writing to files is really quite easy. The good thing is that, as mentioned earlier, because .NET uses the same basic Stream model for a variety of data stores, you can use these same techniques for reading and writing to any of the Stream derived classes. Listing 25-15 shows how you can use the same basic code to write to a MemoryStream , and Listing 25-16 demonstrates reading a Telnet server response using the NetworkStream . Listing 25-15: Writing to a MemoryStream VB Dim data() As Byte = System.Text.Encoding.ASCII.GetBytes("This is a string") Dim ms As New System.IO.MemoryStream() ms.Write(data, 0, data.Length) ms.Close() C# byte[] data = System.Text.Encoding.ASCII.GetBytes("This is a string"); System.IO.MemoryStream ms = new System.IO.MemoryStream(); ms.Write(data, 0, data.Length); ms.Close(); Listing 25-16: Reading from a NetworkStream VB Dim client As New System.Net.Sockets.TcpClient() ’ Note: You can find a large list of Telnet accessible ’ BBS systems at http://www.dmine.com/telnet/brieflist.htm ’ The WCS Online BBS (http://bbs.wcssoft.com) Dim addr As System.Net.IPAddress = System.Net.IPAddress.Parse("65.182.234.52") Dim endpoint As New System.Net.IPEndPoint(addr, 23) client.Connect(endpoint) Dim ns As System.Net.Sockets.NetworkStream = client.GetStream() If (ns.DataAvailable) Then Dim data(client.ReceiveBufferSize) As Byte ns.Read(data, 0, client.ReceiveBufferSize) Dim response As String = System.Text.Encoding.ASCII.GetString(data) End If ns.Close() C# System.Net.Sockets.TcpClient client = new System.Net.Sockets.TcpClient(); // Note: You can find a large list of Telnet accessible // BBS systems at http://www.dmine.com/telnet/brieflist.htm // The WCS Online BBS (http://bbs.wcssoft.com) System.Net.IPAddress addr = System.Net.IPAddress.Parse("65.182.234.52"); System.Net.IPEndPoint endpoint = new System.Net.IPEndPoint(addr,23); 1170 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1171 Chapter 25: File I/O and Streams client.Connect(endpoint); System.Net.Sockets.NetworkStream ns = client.GetStream(); if (ns.DataAvailable) { byte[] bytes = new byte[client.ReceiveBufferSize]; ns.Read(bytes, 0, client.ReceiveBufferSize); string data = System.Text.Encoding.ASCII.GetString(bytes); } ns.Close(); Notice that the concept in both examples is virtually identical. You create a Stream object, read the bytes into a byte array for processing, and then close the stream. The code varies only in the implementation of specific Streams. Readers and Writers Other main parts of I/O in the .NET Framework are Reader and Writer classes. These classes help insulate you from having to deal with reading and writing individual bytes to and from Streams, enabling you to concentrate on the data you are working with. The .NET Framework provides a wide variety of reader and writer classes, each designed for reading or writing according to a specific set of rules. The first table following shows a partial list of the readers available in the .NET Framework. The second table lists the corresponding writer classes. Class Description System.IO .TextReader Abstract class that enables the reading of a sequential series of characters. System.IO .StreamReader Reads characters from a byte stream. Derived from TextReader . System.IO .StringReader Reads textual information as a stream of in-memory characters. Derived from TextReader . System.IO .BinaryReader Reads primitive data types as binary values from a stream. System.Xml .XmlTextReader Provides fast, non-cached, forward-only access to XML. Class Description System.IO .TextWriter Abstract class that enables the writing of a sequential series of characters. System.IO .StreamWriter Writes characters to a stream. Derived from TextWriter . System.IO .StringWriter Writes textual information as a stream of in-memory characters. Derived from TextWriter . 1171 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1172 Chapter 25: File I/O and Streams Class Description System.IO .BinaryWriter Writes primitive data types in binary to a stream. System.Xml .XmlTextWriter Provides a fast, non-cached, forward-only way of generating XML streams or files. Now look at using several different types of readers and writers, starting with a simple e xample. Listing 25-17 shows you how to use a StreamReader to read a FileStream . Listing 25-17: Reading and writing a text file with a StreamReader VB Dim streamwriter As New System.IO.StreamWriter( _ System.IO.File.Open("C: \ Wrox \ temp.txt", System.IO.FileMode.Open) ) streamwriter.Write("This is a string") streamwriter.Close() Dim reader As New System.IO.StreamReader( _ System.IO.File.Open("C: \ Wrox \ temp.txt", System.IO.FileMode.Open) ) Dim tmp As String = reader.ReadToEnd() reader.Close() C# System.IO.StreamWriter streamwriter = new System.IO.StreamWriter( System.IO.File.Open(@"C: \ Wrox \ temp.txt", System.IO.FileMode.Open) ); streamwriter.Write("This is a string"); streamwriter.Close(); System.IO.StreamReader reader = new System.IO.StreamReader( System.IO.File.Open(@"C: \ Wrox \ temp.txt",System.IO.FileMode.Open) ); string tmp = reader.ReadToEnd(); reader.Close(); Notice that when you create a StreamReader , you must pass an existing stream instance as a constructor parameter.Thereaderusesthisstreamasitsunderlying data source. In this sample, you use the File class’s static Open method to open a writable FileStream for your StreamWriter . Also notice that you no longer have to deal with byte arrays. The StreamReader takes care of converting the data to a type that’s more user-friendly than a byte array. In this case, you are using the ReadToEnd method to read the entire stream and convert it to a string. The StreamReader provides a number of different methods for reading data that you can use depending on exactly how you want to read the data, from reading a single character using the Read method, to reading the entire file using the ReadToEnd method. Figure 25-12 shows the results of your write when you open the file in Notepad. 1172 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1173 Chapter 25: File I/O and Streams Figure 25-12 Now use the BinaryReader and BinaryWriter classestoreadandwritesomeprimitivetypestoafile. The BinaryWriter writes primitive objects in their native format, so in order to read them using the BinaryReader , you must select the appropriate Read method. Listing 25-18 shows you how to do that; in this case, you are writing a value from a number of different primitive types to the text file, then reading the same value. Listing 25-18: Reading and writing binary data VB Dim binarywriter As New System.IO.BinaryWriter( _ System.IO.File.Create("C: \ Wrox \ binary.dat")) binarywriter.Write("a string") binarywriter.Write(&H12346789ABCDEF) binarywriter.Write(&H12345678) binarywriter.Write("c"c) binarywriter.Write(1.5F) binarywriter.Write(100.2D) binarywriter.Close() Dim binaryreader As New System.IO.BinaryReader( _ System.IO.File.Open("C: \ Wrox \ binary.dat", System.IO.FileMode.Open)) Dim a As String = binaryreader.ReadString() Dim l As Long = binaryreader.ReadInt64() Dim i As Integer = binaryreader.ReadInt32() Dim c As Char = binaryreader.ReadChar() Dim f As Double = binaryreader.ReadSingle() Dim d As Decimal = binaryreader.ReadDecimal() binaryreader.Close() C# System.IO.BinaryWriter binarywriter = new System.IO.BinaryWriter( System.IO.File.Create(@"C: \ Wrox \ binary.dat") ); binarywriter.Write("a string"); binarywriter.Write(0x12346789abcdef); Continued 1173 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1174 Chapter 25: File I/O and Streams binarywriter.Write(0x12345678); binarywriter.Write(’c’); binarywriter.Write(1.5f); binarywriter.Write(100.2m); binarywriter.Close(); System.IO.BinaryReader binaryreader = new System.IO.BinaryReader( System.IO.File.Open(@"C: \ Wrox \ binary.dat", System.IO.FileMode.Open)); string a = binaryreader.ReadString(); long l = binaryreader.ReadInt64(); int i = binaryreader.ReadInt32(); char c = binaryreader.ReadChar(); float f = binaryreader.ReadSingle(); decimal d = binaryreader.ReadDecimal(); binaryreader.Close(); If you open this file in Notepad, you should see that the BinaryWriter has written the nonreadable binary data to the file. Figure 25-13 shows what the content o f the file looks like. The BinaryReader provides a number of different methods for reading various kinds of primitive types from the stream. In this sample, you use a different Read method for each primitive type that you write to the file. Figure 25-13 Finally, notice that the basic usage of both the StreamReader / StreamWriter and BinaryReader / BinaryWriter classes is virtually identical. You can apply the same basic ideas to use any of the reader or writer classes. Encodings The StreamReader by default attempts to determine the encoding format of the file. If one of the sup- ported encodings such as UTF-8 or UNICODE is detected, it is used. If the encoding is not recognized, the default encoding of UTF-8 is used. Depending on the constructor you call, you can change the default encoding used and optionally turn off encoding detection. The following example shows how you can control the encoding that the StreamReader uses. StreamReader reader = new StreamReader(@"C: \ Wrox \ text.txt",System.Text.Encoding.Unicode); 1174 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1175 Chapter 25: File I/O and Streams The default encoding for t he StreamWriter is also UTF-8, and you can override it in the same manner as the StreamReader class. I/O Shortcuts Although knowing how to create and use streams is always very useful and worth studying, the .NET Framework provides you with numerous shortcuts for common tasks like reading and writing to files. For instance, if you want to read the entire file, you can simply use one of the static Read All methods of the File class. Using these methods, you cause .NET to handle the process of creating the Stream and StreamReader for you, and simply return the resulting string of data. This is just one example of the shortcuts that the .NET Framework provides. Listing 25-19 shows some of the others, with explanatory comments. Keep in mind that Listing 25-19 is showing individual code snippets; do not try to run the listing as a single block of code. Listing 25-19: Using the static method of the File and Directory classes VB ’ Opens a file and returns a FileStream Dim fs As System.IO FileStream = _ System.IO.File.Open("C: \ Wrox \ temp.txt", System.IO.FileMode.Open) ’ Opens a file and returns a StreamReader for reading the data Dim sr As System.IO.StreamReader = System.IO.File.OpenText("C: \ Wrox \ temp.txt") ’ Opens a filestream for reading Dim fs As System.IO.FileStream = System.IO.File.OpenRead("C: \ Wrox \ temp.txt") ’ Opens a filestream for writing Dim fs As System.IO.FileStream = System.IO.File.OpenWrite("C: \ Wrox \ temp.txt") ’ Reads the entire file and returns a string of data Dim data As String = System.IO.File.ReadAllText("C: \ Wrox \ temp.txt") ’ Writes the string of data to the file System.IO.File.WriteAllText("C: \ Wrox \ temp.txt", data) C# // Opens a file and returns a FileStream System.IO.FileStream fs = System.IO.File.Open(@"C: \ Wrox \ temp.txt", System.IO.FileMode.Open); // Opens a file and returns a StreamReader for reading the data System.IO.StreamReader sr = System.IO.File.OpenText(@"C: \ Wrox \ temp.txt"); // Opens a filestream for reading Continued 1175 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1176 Chapter 25: File I/O and Streams System.IO.FileStream fs = System.IO.File.OpenRead(@"C: \ Wrox \ temp.txt"); // Opens a filestream for writing System.IO.FileStream fs = System.IO.File.OpenWrite(@"C: \ Wrox \ temp.txt"); // Reads the entire file and returns a string of data string data = System.IO.File.ReadAllText(@"C: \ Wrox \ temp.txt"); // Writes the string of data to the file System.IO.File.WriteAllText(@"C: \ Wrox \ temp.txt", data); Compressing Streams Introduced in the .NET 2.0 Framework, the System.IO.Compression namespace includes classes for compressing and decompressing data using either the GZipStream or the DeflateStream classes. GZip Compression Because both new classes are derived from the Stream class, using them should be relatively similar to using the other Stream operations you have examined so far in this chapter. Listing 25-20 shows an example of compressing your text file using the GZipStream class. Listing 25-20: Compressing a file using GZipStream VB ’ Read the file we are going to compress into a FileStream Dim filename As String = Server.MapPath("TextFile.txt") Dim infile As System.IO.FileStream = System.IO.File.OpenRead(filename) Dim buffer(infile.Length) As Byte infile.Read(buffer, 0, buffer.Length) infile.Close() ’ Create the output file Dim outfile As System.IO.FileStream = _ System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "zip")) ’ Compress the input stream and write it to the output FileStream Dim gzipStream As New System.IO.Compression.GZipStream( outfile, System.IO.Compression.CompressionMode.Compress) gzipStream.Write(buffer, 0, buffer.Length) gzipStream.Close() C# // Read the file we are going to compress into a FileStream string filename = Server.MapPath("TextFile.txt"); System.IO.FileStream infile = System.IO.File.OpenRead(filename); byte[] buffer = new byte[infile.Length]; 1176 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1177 Chapter 25: File I/O and Streams infile.Read(buffer, 0, buffer.Length); infile.Close(); // Create the output file System.IO.FileStream outfile = System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "zip")); // Compress the input stream and write it to the output FileStream System.IO.Compression.GZipStream gzipStream = new System.IO.Compression.GZipStream(outfile, System.IO.Compression.CompressionMode.Compress); gzipStream.Write(buffer, 0, buffer.Length); gzipStream.Close(); Notice that the GZipStream constructor requires two parameters, the stream to write the compressed data to, and the CompressionMode enumeration, which tells the class if you want to compress or decompress data. After the code runs, be sure there is a file called text.zip in your Web site directory. Deflate Compression The Compression namespace also allows to you decompress a file using the GZip or Deflate methods. Listing 25-21 shows an example of decompressing a file using the Deflate method. Listing 25-21: Decompressing a file using DeflateStream VB Dim filename As String = Server.MapPath("TextFile.zip") Dim infile As System.IO.FileStream = System.IO.File.OpenRead(filename) Dim deflateStream As New System.IO.Compression.DeflateStream( _ infile, System.IO.Compression.CompressionMode.Decompress) Dim buffer(infile.Length + 100) As Byte Dim offset As Integer = 0 Dim totalCount As Integer = 0 While True Dim bytesRead As Integer = deflateStream.Read(buffer, offset, 100) If bytesRead = 0 Then Exit While End If offset += bytesRead totalCount += bytesRead End While Dim outfile As System.IO.FileStream = _ System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "txt")) outfile.Write(buffer, 0, buffer.Length) outfile.Close() C# string filename = Server.MapPath("TextFile.zip"); System.IO.FileStream infile = System.IO.File.OpenRead(filename); Continued 1177 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1178 Chapter 25: File I/O and Streams System.IO.Compression.DeflateStream deflateStream = new System.IO.Compression.DeflateStream(infile, System.IO.Compression.CompressionMode.Decompress); byte[] buffer = new byte[infile.Length + 100]; int offset = 0; int totalCount = 0; while (true) { int bytesRead = deflateStream.Read(buffer, offset, 100); if (bytesRead == 0) { break; } offset += bytesRead; totalCount += bytesRead; } System.IO.FileStream outfile = System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "txt")); outfile.Write(buffer, 0, buffer.Length); outfile.Close(); Compressing HTTP Output Besides compressing files, one other very good use of the compression feature s of the .NET Framework in an ASP.NET application is to implement your own HttpModule class that compresses the HTTP output of your application. This is easier than it might sound, and it will save you precious bandwidth by com- pressing the data that is sent from your Web server to the browsers that support the HTTP 1.1 Protocol standard (which most do). The browser can then decompress the data before rendering it. IIS 6 d oes offer built-in HTTP compression capabilities, and there are several third-party HTTP com- pression modules available, such as the Blowery Http Compression Module ( www.blowery.org ). Start by creating a Windows Class library project. Add a new class to your project called Compression- Module . This class is your compression HttpModule . Listing 25-22 shows the code for creating the class. Listing 25-22: Compressing HTTP output with an HttpModule VB Imports System Imports System.Collections.Generic Imports System.Text Imports System.Web Imports System.IO Imports System.IO.Compression Namespace Wrox.Demo.Compression Public Class CompressionModule Implements IHttpModule Continued 1178 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1179 Chapter 25: File I/O and Streams Public Sub Dispose() Implements System.Web.IHttpModule.Dispose Throw New Exception("The method or operation is not implemented.") End Sub Public Sub Init(ByVal context As System.Web.HttpApplication) _ Implements System.Web.IHttpModule.Init AddHandler context.BeginRequest, AddressOf context_BeginRequest End Sub Public Sub context_BeginRequest(ByVal sender As Object, ByVal e As EventArgs) Dim app As HttpApplication = CType(sender, HttpApplication) ’Get the Accept-Encoding HTTP header from the request. ’The requesting browser sends this header which we will use ’ to determine if it supports compression, and if so, what type ’ of compression algorithm it supports Dim encodings As String = app.Request.Headers.Get("Accept-Encoding") If (encodings = Nothing) Then Return End If Dim s As Stream = app.Response.Filter encodings = encodings.ToLower() If (encodings.Contains("gzip")) Then app.Response.Filter = New GZipStream(s, CompressionMode.Compress) app.Response.AppendHeader("Content-Encoding", "gzip") app.Context.Trace.Warn("GZIP Compression on") Else app.Response.Filter = _ New DeflateStream(s, CompressionMode.Compress) app.Response.AppendHeader("Content-Encoding", "deflate") app.Context.Trace.Warn("Deflate Compression on") End If End Sub End Class End Namespace C# using System; using System.Collections.Generic; using System.Text; using System.Web; using System.IO; using System.IO.Compression; namespace Wrox.Demo.Compression { public class CompressionModule : IHttpModule Continued 1179 . string"); binarywriter.Write(0x1 234 6789abcdef); Continued 11 73 Evjen c 25. tex V2 - 01/28/2008 3: 42pm Page 1174 Chapter 25: File I/O and Streams binarywriter.Write(0x1 234 56 78); binarywriter.Write(’c’); binarywriter.Write(1.5f); binarywriter.Write(100.2m); binarywriter.Close(); System.IO.BinaryReader. a MemoryStream , and Listing 25- 16 demonstrates reading a Telnet server response using the NetworkStream . Listing 25- 15: Writing to a MemoryStream VB Dim data() As Byte = System.Text.Encoding.ASCII.GetBytes("This. binaryreader.ReadString(); long l = binaryreader.ReadInt64(); int i = binaryreader.ReadInt32(); char c = binaryreader.ReadChar(); float f = binaryreader.ReadSingle(); decimal d = binaryreader.ReadDecimal(); binaryreader.Close(); If