SerializationWhat is Serialization

• Serialization is the process of converting an object, or a connected graph of objects, stored within computer memory, into a linear sequence of bytes

• Use the sequence of bytes in several ways:– Send it to another process– Send it to the clipboard, to be browsed or used by

another application– Send it to another machine– Send it to a file on disk

SerializationObject Graph

• What is an object graph? – An object graph is a set of objects with some set

of references to each other– The most obvious problem is how to represent the

links between the objects in the Serialized stream

CatCat Mouse

Duck

Dog

2

1

3

4

9

7

Horse

SerializationHow Serialization Works

• Because run-time metadata 'knows' about each object's layout in memory, and its field and property definitions, you can serialize objects automatically, without having to write code to serialize each field

• The serialized stream might be encoded using XML, or a compact binary representation

• The format is decided by the the Formatter object that you call:– Binary– SOAP– Custom

Serializaiton Example - VideoLibrary

using System; namespace VideoLibrary { [Serializable] public enum Genre { Drama, Comedy, Western, ScienceFiction, Horror, Family }; [Serializable] public class VideoInfo { public string Title { get; set; } public Genre Category { get; set; } public string Director { get; set; } public int Year { get; set; } public TimeSpan Duration { get; set; } public string Review { get; set; } } }

Worksheet 4 from http://www.cse.ohio-state.edu/~crawfis/cse459_CSharp/index.html

Serializaiton Example - VideoLibrary

namespace VideoLibrary { public partial class MyVideoLibraryForm : Form { List<VideoInfo> videoLib = new List<VideoInfo>();… private void saveLibraryToolStripMenuItem_Click(object sender, EventArgs e) { if (this.saveLibraryDialog.ShowDialog() == DialogResult.OK) { XmlSerializer s = new XmlSerializer(videoLib.GetType()); using (TextWriter w = new StreamWriter(saveLibraryDialog.FileName)) { s.Serialize(w, videoLib); } } }

Worksheet 4 from http://www.cse.ohio-state.edu/~crawfis/cse459_CSharp/index.html

File->Save menu

Serializaiton Example - VideoLibrary

private void openToolStripMenuItem_Click(object sender, EventArgs e) { if (this.openLibraryDialog.ShowDialog() == DialogResult.OK) { XmlSerializer s = new XmlSerializer(videoLib.GetType()); using (TextReader reader = new StreamReader(openLibraryDialog.FileName)) { List<VideoInfo> newVideos = (List<VideoInfo>)s.Deserialize(reader); foreach( VideoInfo video in newVideos) bindingVideoLib.Add(video); } } }

Worksheet 4 from http://www.cse.ohio-state.edu/~crawfis/cse459_CSharp/index.html

File->Import menu

Serialization Scenarios

• Persistence• Remoting-By-Value• Remoting-By-Reference• Transacted Persistence

SerializationBasic Serialization

• A Type is NOT Serializable unless Type is specifically marked as Serializable

• The Serializable Attribute

• The Non-Serializable Attribute

[Serializable] public class MyClass {}

[Serializable] public class MyClass { [NotSerialized] int _cashSize;

}

Serialization

• It is easy to write the individual fields of a record object to a file

• For example, we can create a record that stores information about a student– Name– Address– ID number– Course enrolled for– etc

• We can output each field of this record to a file (either text or binary)

Serialization

StudentInfo

NameAddressID numberCourse Info

Record filestring string int string

Serialization• In this example, any program that needs to read the file

needs to know the format of the data– 2 strings, an int and then a string– Also whether each item is on a separate line

• .NET serialization allows complete objects to be read or written with a single statement (.NET does the plumbing for you using reflection).

• A serialized object is an object represented as a sequence of bytes.

• Information is stored about the data types of the objects instance fields as well as their values– Allows the object to be reconstructed (de-serialized)

from the sequence of bytes.

Serialization

StudentInfo

NameAddressID numberCourse Info

Record fileStudentInfo object

Serialization• To serialize an object, the object class needs to be

marked with the [Serializable] attribute or needs to implement the ISerializable interface

• Requires the System.Runtime.Serialization namespace

• Also we require a formatter to serialize/de-serialize the object before writing to or reading from file– IFormatter - BinaryFormatter– XMLSerializer (why is this not an IFormatter?)

SerializationISerializable Interface

• Customize the serialization process• If a class implements ISerializable, that

interface will always be called in preference to default serialization.

• The ISerializable interface only contains one method:

void GetObjectData (SerializationInfo info, StreamingContext context); And an implied constructor that may be private. private <T> (SerializationInfo info, StreamingContext)

SerializationAdditional Attributes

• The serialization framework allows you to also specify methods to be called when an instance is being deserialized, after it is deserialized, before it is serialized, etc.– [OnDeserialized] – see the MSDN example.

SerializationIDeserializationEventListener

• If an object implements IDeserializationEventListener, the serialization infrastructure will call that class‘ OnDeserialization method as soon as the entire graph has been deserialized and all fix-ups completed

• Provide a reasonable opportunity for objects that need to do fix-ups based on the state of their children

Serialization

• Binary serialization is limited as only .NET applications can deserialize the data stream

• For more general inter-operability especially across a network, xml serialization is used– xml is text based and self descibing and

universal– Comprised name/attribute pairs– xml serialization easy to implement and uses

text streams

Serialization• We need to insert xml tags into our

StudentInfo class– Only public properties and fields can be

serialized

[XmlRoot("studentInfo")]public class StudentInfo{ [XmlAttribute("name")] public string Name; [XmlAttribute("address")] public string Address; [XmlAttribute("course")] public string CourseInfo; [XmlAttribute("id")] private int ID; public StudentInfo() { }

public StudentInfo(String n, String a, String ci, int id) { Name = n; Address = a; CourseInfo = ci; ID = id; }}