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<h1>Logging Storage</h1>
<p>In this example we will implement a simple file base
storage, which will log messages about each IO operation. In the implementation
you can see that most of the functionality is derived from StorageDecorator and
BinDecorator classes with additional logging added:</p>
<p MadCap:conditions="Global.Primary:java" />
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<pre class="prettyprint" xml:space="preserve">LoggingStorage.cs
/**//* Copyright (C) 2004 - 2009 Versant Corporation http://www.versant.com */
using System;
using Db4objects.Db4o.IO;
namespace Db4odoc.<span class="MCPopup"><a href="javascript:void(0);" class="MCPopupSpot" onclick="FMCPopup( event, this ); return false;" MadCap:src="../../storage.htm">Storage<img style="border: none;margin-left: 5px;" src="../../../../SkinSupport/ExpandingClosed.gif" MadCap:altsrc="../../../../SkinSupport/ExpandingOpen.gif" class="MCExpandingIcon" onload="if ( typeof( FMCPreloadImage ) == 'function' ) { FMCPreloadImage( '../../../../SkinSupport/ExpandingOpen.gif' ); }" /></a></span>
{
class LoggingStorage : StorageDecorator
{
// delegate to a normal file storage
public LoggingStorage()
: base(new FileStorage())
{
}
// use submitted storage as a delegate
public LoggingStorage(IStorage storage)
: base(storage)
{
}
/**//**
* opens a Bin for the given URI.
*/
public override IBin Open(BinConfiguration config)
{
IBin storage = base.Open(config);
if (config.ReadOnly())
{
return new ReadOnlyBin(new LoggingBin(storage));
}
return new LoggingBin(storage);
}
/**//// <summary>
/// LoggingBin implementation. Allows to log information
/// for each IO operation
/// </summary>
class LoggingBin : BinDecorator
{
public LoggingBin(IBin bin)
: base(bin)
{
}
// delegate to the base class and log a message
public override void Close()
{
base.Close();
System.Console.WriteLine(string.Format
("{0} LoggingStorage: File closed", DateTime.Now.ToString()));
}
// log a message, then delegate
public override int Read(long pos, byte[] buffer, int length)
{
System.Console.WriteLine(
string.Format("{0} LoggingStorage: Reading {1} bytes and {2} position",
DateTime.Now.ToString(), length, pos));
return base.Read(pos, buffer, length);
}
// log a message, then delegate
public override void Write(long pos, byte[] buffer, int length)
{
System.Console.WriteLine(
string.Format("{0} LoggingStorage: Writing {1} bytes and {2} position",
DateTime.Now.ToString(), length, pos));
base.Write(pos, buffer, length);
}
// log a message, then delegate
public override void Sync()
{
System.Console.WriteLine(
string.Format("{0} LoggingStorage: Syncing", DateTime.Now.ToString()));
base.Sync();
}
}
}
}</pre>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<pre class="prettyprint lang-vb" xml:space="preserve">LoggingStorage.vb
' Copyright (C) 2004 - 2009 Versant Corporation http://www.versant.com
Imports System
Imports Db4objects.Db4o.IO
Namespace Db4odoc.Storage
Class LoggingStorage
Inherits StorageDecorator
Public Sub New()
' delegate to a normal file storage
MyBase.New(New FileStorage())
End Sub
Public Sub New(ByVal storage As IStorage)
' use submitted storage as a delegate
MyBase.New(storage)
End Sub
'
' opens a logging bin for the given URI.
'
Public Overloads Overrides Function Open(ByVal config _
As BinConfiguration) As IBin
Dim storage As IBin = MyBase.Open(config)
If config.[ReadOnly]() Then
Return New ReadOnlyBin(New LoggingBin(storage))
End If
Return New LoggingBin(storage)
End Function
' LoggingBin implementation. Allows to log information
' for each IO operation
Private Class LoggingBin
Inherits BinDecorator
Public Sub New(ByVal bin As IBin)
MyBase.New(bin)
End Sub
' delegate to the base class and log a message
Public Overloads Overrides Sub Close()
MyBase.Close()
System.Console.WriteLine( _
String.Format("{0} LoggingStorage: File closed", DateTime.Now.ToString()))
End Sub
' log a message, then delegate
Public Overloads Overrides Function Read(ByVal _
pos As Long, ByVal buffer As Byte(), _
ByVal length As Integer) As Integer
System.Console.WriteLine( _
String.Format("{0} LoggingStorage: Reading {1} bytes and {2} position", _
DateTime.Now.ToString(), length, pos))
Return MyBase.Read(pos, buffer, length)
End Function
' log a message, then delegate
Public Overloads Overrides Sub Write(ByVal pos As Long, _
ByVal buffer As Byte(), ByVal length As Integer)
System.Console.WriteLine(_
String.Format("{0} LoggingStorage: Writing {1} bytes and {2} position", _
DateTime.Now.ToString(), length, pos))
MyBase.Write(pos, buffer, length)
End Sub
' log a message, then delegate
Public Overloads Overrides Sub Sync()
System.Console.WriteLine( _
String.Format("{0} LoggingStorage: Syncing", DateTime.Now.ToString()))
MyBase.Sync()
End Sub
End Class
End Class
End Namespace</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>Use the LoggingStorage implementation with the following
code (you can find a working example if you download LoggingStorage class).</p>
<p MadCap:conditions="Global.Primary:java" />
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<p>C#:</p>
<p><code>config.File.Storage(new LoggingStorage());</code>
</p>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<p>VB.NET:</p>
<p><code>config.File.Storage(New LoggingStorage())</code>
</p>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p MadCap:conditions="Primary.Online">Download example code:</p>
<p MadCap:conditions="Primary.Online">
<MadCap:conditionalText MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages"><a href="storagevb.zip">VB.NET </a>
</MadCap:conditionalText>
<MadCap:conditionalText MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><a href="storagecs.zip">c# </a>
</MadCap:conditionalText>
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