Tài liệu Appendix: Isolated Storage docx

Isolated storage is a Microsoft® .NET feature that is used for lightweight data persistence.. This appendix provides the explanation of isolated storage and then describes the limitation

Appendix: Isolated Storage

What Is Isolated Storage?

Isolated storage is a Microsoft® NET feature that is used for lightweight data persistence This appendix provides the explanation of isolated storage and then describes the limitations of isolated storage Also covered is using isolated storage to persist user preferences and application state

Isolated storage is an alternative to persistently storing data in a file or in a database When a Web application stores data in a file, the file name and storage location must be chosen carefully If the file name and storage location are not chosen carefully, there is a possibility that the storage location will be known to another Web application, which can then make the original Web application vulnerable to attack Isolated storage manages this problem by providing a separate database storage mechanism that provides isolation by defining standardized ways of associating code with saved data In isolated storage, data is stored in a logical storage compartment Each storage compartment is isolated by some aspects of the code's identity These identifying aspects of the code can include the application domain, assembly, and user For the developer, the actual location of the storage compartment is transparent Only the identity aspects are required to access the compartment Microsoft ASP.NET Web applications, by default, cannot use file input/output (I/O) Isolated storage is useful in ASP.NET Web applications for storing user preferences and application state

Isolated storage is not a secure storage medium Isolated storage is not protected from highly trusted code, from unmanaged code, or from trusted users

Isolated storage should not be used to store configuration settings that an administrator might want to control Configuration files are a better location for configuration settings because they are more easily edited and installed by administrators

Isolated storage is a lightweight alternative to database storage when the number of users is small, when the overhead of a database is too high, or when

a database is not available

Introduction

Uses in a Web

application

Limitations

2 Appendix: Isolated Storage

Using Isolated Storage

Administrators can limit how much isolated storage should be available to a Web application or a user for use, based on the appropriate trust level To create and access isolated storage, code must be granted the appropriate

IsolatedStorageFilePermission attribute

The System.IO.IsolatedStorage.IsolatedStorageFile class is used to create

and access isolated storage compartments This class contains methods that can

be used for creating, opening, and deleting compartments, in addition to containing methods that can be used for adding folders to storage compartments

The System.IO.IsolatedStorage.IsolatedStorageFileStream class is used to

open streams on files within isolated storage These streams can then be used to read and write data to isolated storage

The following code segment uses the IsolatedStorageFile class to create a new

store by using the User, Domain, and Assembly identities The code segment then creates a new directory, named Files, within that store The code then uses

the IsolatedStorageFileStream class to create a new file in the Files directory

Finally, both the stream and the storage are closed, as shown in the following code example:

[Visual Basic]

Dim store As IsolatedStorageFile store = IsolatedStorageFile.GetStore( _ IsolatedStorageScope.User Or _ IsolatedStorageScope.Domain Or _ IsolatedStorageScope.Assembly, Nothing, Nothing) store.CreateDirectory("Files")

Dim stream As IsolatedStorageFileStream stream = New IsolatedStorageFileStream("settings.txt", _ FileMode.Create, store)

' Use the Write method to set the file's contents

stream.Close() store.Close() [C#]

IsolatedStorageFile store = IsolatedStorageFile.GetStore(IsolatedStorageScope.User | IsolatedStorageScope.Domain |

IsolatedStorageScope.Assembly, null, null);

store.CreateDirectory("Files");

IsolatedStorageFileStream stream = new IsolatedStorageFileStream("settings.txt", FileMode.Create, store);

//

// Use the Write method to set the file's contents stream.Close();

store.Close();

Introduction

Supporting types

Appendix: Isolated Storage 3

The isolated storage tool (StoreAdm.exe) is a command-line utility that can be used to list and delete isolated storage compartments on a computer

StoreAdm.exe supports the switches that are specified in the following table

Switch Description /list Lists the isolated storage for the current user

/remove Removes all of the existing isolated storage for the current user

/roaming Selects roaming storage Assumes that roaming is supported by the

underlying operating system

/quiet Changes the output to display only error messages and no informational

messages

After running the preceding code in a console application named IsoStore.exe,

the /list switch will provide the stores that are shown in the following code

example:

Microsoft (R) NET Framework Store Admin 1.0.3705.0 Copyright (C) Microsoft Corporation 1998-2001 All rights reserved

Record #1 [Domain]

<System.Security.Policy.Url version="1">

<Url>file://C:/Demos/IsoStore.exe</Url>

</System.Security.Policy.Url>

[Assembly]

<System.Security.Policy.Url version="1">

<Url>file://C:/Demos/IsoStore.exe</Url>

</System.Security.Policy.Url>

Size : 2048

StoreAdm.exe

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