What is a serializable object in C#?
I guess the word serializable is throwing me off more than "serializable object".
Normally objects are random access, that is, you can specify any part of an object (property or field) and access that part directly. That's all well and fine if you're using RAM to store an object, because RAM is Random Acess Memory and is therefore suited to the job.
When you need to store your object on a medium that is not traditionally random access, for instance disk, or you need to transfer an object over a stream medium (such as the network) then the object needs to be converted into a form that is suitable to the relevant medium. This conversion process is called serialization, because the structured object is flattened or serialized, making it more amenable to being stored for the long term, or transferred over the network.
Why not just copy the bits comprising the object in RAM to disk, or send it as an opaque blob over the network? ... you may ask. A few issues:
Often the format that the object is stored in memory is proprietary and therefore not suitable for public consumption--the way in which it is stored in memory is optimised for in-memory use.
When an object references other objects, those references only have meaning within the context of the running application. It would not be possible to deserialize the object meaningfully unless during the serialization process, the object graph was walked and serialized accordingly. There may be a need to translate those references into a form that has meaning outside the context of an application instance.
There may be an interoperability requirement between heterogeneous systems, in which case a standard means of representing the object is required (typically some form of XML is chosen for this).
An object that can be converted to bits and stored on a medium, such as a hard drive.
http://en.wikipedia.org/wiki/Serialization
Object serialization is storing the instance's state so you can reconstruct that instance again later.
In most (C# and Java), a serializable object is "marked". In Java you need to implement Serializable. In C# you need to use [Serializable].
Once the object is serialized you can store it in a file or send it over the network.
Think of it like going through every instance variable of an instance and storing its value, separated by some separator (although, it's a lot more sophisticated than that; think of what happens if you have instance variables of non-primitive types, you're gonna have to store all the values inside those, too).
One use of it would be saving a game.
Serializing in general means to save an objects state into a 'saveable' format (like saving to disk) so that it can be deserialized later on into an actual object. It is usually done to also send an object over the network in case of remote calls. If you dont want save and also if you dont want to send an object over the wire you can ignore the serializable part (in Java you dont implement the Serializable interface)
You can mark an object as [serializable] in C#, which mean that it can be converted to binary, SOAP, XML, in .net anyhow.
The beauty of this is that you can serialize an object send it across the internet, network etc then reinstate it on the other side as an object again. This can then cross machine boundaries, such as a windows machine to a Unix machine as long as the Computer on the other side is able to read the data and de-serialize it.
See this article:
http://www.devhood.com/Tutorials/tutorial_details.aspx?tutorial_id=236
In addition to what has been said, I think it's important to mention that serialization of data implies giving it a well defined order (serial comes from series, which means having something lined up or in line).
For instance, serializing a graph (e.g. an RDF graph as known from the "semantic web") into a serialization format such as XML means that there must be a ruleset defining how to put the information contained in the graph into an order, so that it can later be reconstructed by applying the reverse serialization rule (deserializing it).
Serialization :its a technique to convert object into binary format,simple object access protocol(SOAP) , or xml documents that can be easily stored ,transfered and retrieved .
In simple way serialization way that we can compress and decompress the data and transfer the data across network in a secure way.
object serialization is what ljuwaidah explained .
Try this link also
link text
As Java is an platform independent and it was invented for teh security purpose, all the things are possible in the form of bit. For example, we, as a user are quite understand the alphabets but it would be difficult to remember the bits of that alphabets or we can say in that Java language string.
Therefore to provide the security in the networking we use the objects.
As the messages are lossly coupled, to provide the security we use the objects to send or receive the messages from server or from client. Therefore as we are using the objects the objects must be serializable means they must be in the form of bits that can be easily understood by the machine.
Particularly to send and receive the message is known as JMS(Java Message Service) is used. For example, one computer which is in India may want to communicate with another computer which is in the U.S. at that time, JMS service is used.
In short the serialization means to convert the strings into to the bits.
By using this we can create the Java programs such as to send the mails and receives like the mail application based on the SMTP(Simple Mail Transfer Protocol) protocol is used.
Related
I was just wondering about XML Serialization. If i understand correctly, the main reason for using it is that it lets you transport your object data more easily, am I right? Also, i tried serializing data using a constructor but it says that that you can only serialize data that are "parameterless". The thing is I like constructors because it allows me to have for example a Player class, and adding a new player with all properties is much more productive than having to set all properties one by one.
So the big question here is, what's the BIG purpose of XML serialization, what are the ways to use it? the way I see it is that it adds another level of complexity to my code, because i now need a class to serialize my data. Can someone shed some light?!
If you're talking about the overall purpose of serialization, strictly speaking, serialization (note that I said "serialization," not "XML Serialization" - more on that in a second) doesn't just make transporting objects easier, it's the only way you could transport an object.
As indicated in Pablo Santa Cruz's answer, XML is one of many ways you can serialize data. If you're going to save or send data somewhere, by definition you must first have some way to represent it. Serialization basically means that you represent your object state in some specified format. Deserialization is the opposite - given some representation of an object state, reconstruct what the original object state was.
In that sense, XML serialization, saving an object state to a database somehow, saving it as JSON, saving it in some binary format, and saving in some XML format are all examples of serialization (because you're representing the object state in a pre-defined format for later use).
While any defined format can technically be serialization, there are several standard ways of doing that. XML and JSON are by far the most common formats because they're standardized, easy to parse, easy to constrain (e.g. with XML Schema), are widely supported by libraries, can be relatively human-readable (which makes debugging easier), and they're widely used.
In case the last point sounds a little odd (they're widely used because they're widely used), standards by their very nature tend to have a strong network effect. In other words, the more people adapt them the more useful they are; for example, it's only useful to have email if you can actually use it to contact other people - it wouldn't be even slightly useful to have email if you were the only one using it.
A lot of standards and technologies will win out over competitors more because they have more early adapters than because they're necessarily technically superior. For example, even if someone could clearly prove that OS X is a "better" operating system than Windows, it wouldn't matter because there's vastly more software developed for Windows and it would be prohibitively expensive for people to try to switch to OS X. (You could make a similar argument for Token Ring vs. Ethernet).
Serialization is for storing object representation somehow (on a disk file, on the wire {network transportation}, on a HTTP session, on a database). XML Serialization is just one type of serialization.
The reason you need a parameter-less constructor to support serialization, is that the AUTO DESERIALIZER needs to create an EMPTY (with no o little data) class before start populating it with the corresponding data.
You don't need to use ONE WAY or THE OTHER, because you can have a class with multiple constructor (the parameter-less one will be used on deserialization, and you can use the other one wherever you need in your code).
Assuming all fields of a java class are java primitives, if such an object has been serialized, can it be successfully deserialized by C# into an instance of an "equivalent" C# class?
Is the reverse possible - C# to java?
I realise there are many language agnostic formats, such as XML that could be used to get the job done. I am more interested in whether using the native serialized data is feasible.
The formats of serialized streams are available. I think you can write a class easily to parse the byte stream and create the required class in C#.
An article that specifies the serialized format:
http://www.javaworld.com/community/node/2915
WOX will be helpful to achieve interoperable serialization.
it can serialize/deserialize Java/C# objects into/from standard XML(platform independent)
This is not possible, at least not using the native serialization libraries that both frameworks provide, as stated in this previous SO post.
If you want to achieve cross language serialization/deserialization, you could resort to XML (XSTream for Java, XStream-dot-net for C#) or WOX:
WOX is an XML serializer for Java and C# objects. In other words, WOX
is a library (woxSerializer.jar for Java, and woxSerializer.dll for
C#) to serialize Java and C# objects to XML and back again.
If you're OK with including another dependency, you might consider using an object database such as db4o for the job. I haven't tried this myself, but according the Wikipedia article,
db4o uses a custom feature called "generic reflector" to represent class information, when class definitions are not available, which allows to use it in a mixed Java-.NET environment, for example Java client - .NET server and vice versa.
You can find more information about the above-mentioned reflection API here and here.
In a nutshell, this would lead to a system where you store your Java/C# objects to an (embedded) database (i.e., without client/server architecture, but by loading a single file that contains the whole database) and retrieve C#/Java objects from the database afterwards.
I have used this document with a high amount of success to parse data stored in serialized format on a database:
http://www.jtech.ua.es/j2ee/2005-2006/modulos/rmi/recursos/serial-1.5.0.pdf
The most meaningful info for me was from page 63 to 68.
In my case I had the source code used to serialize the data which was useful to both identify fields and read the data when was written in a non standard way using the ISerializable.WriteObject/ReadObject calls.
I don't know the reason but my serialized data had not "handler" field on any object, it would take 0 bytes. Other than that, everything followed the docs but it gets kind of tricky if you have never done such kind of tasks before
As noted on some comment, this is a good base even if it's written in java:
https://github.com/smartplatf/a-utilities/blob/master/src/main/java/org/anon/utilities/serialize/srdr/SerialStreamReader.java
Ok. I know how to use Serialization and such, but since that only applies to Objects that's been marked with Serialization attribute - how can I for example load data and use it in an application without using Serialization? Say a data file.
Or, create a datacontainer with serialization that holds files not serialized.
Methods I've used is Binary Serialization and XML Serialization. Any other ways that can load unknown data and perhaps somehow use it in C#?
JSON serialization using JSON.NET
This eats everything! Including anonymous types.
Edit
I know you said "you don't want serialization", but based on your statement "[...]Objects that's been marked with Serialization attribute", I believe you didn't try JSON serialization using JSON.NET!
Maybe a definition of terms is in order; serialization is "the process of converting a data structure or object state into a format that can be stored and "resurrected" later in the same or another computer environment". Pretty much any method of converting "volatile" memory into persistent data and back is "serialization", so even if you roll your own scheme to do it, you're "serializing".
That said, it sounds like you simply don't want to use .NET binary serialization. That's actually the right idea; binary serialization is simple, but very code- and environment-dependent. Moving a serializable class to a different namespace, or serializing a file using the Microsoft CLR and then trying to deserialize it in Mono, can break binary serialization.
First and foremost, you MUST be able to determine what type of object you should try to create based on the file. You simply cannot open some "random" file and expect to be able to get anything meaningful out of it without knowing how the data is structured within the file. The easiest way is for the file to tell you, by specifying the type name of the object it was created from (which you will hopefully have available in your codebase). Most built-in serializers do it this way. Other ways the file can inform consumers of its format include file, row and/or field header codes (very common in older standards as they economize on file size) and extension/MIME type.
With that sorted out, deserialization can take place. If the file was serialized using a built-in serializer, simply use that, but if it's an older format (CSV, fixed-length) then you will have to parse the file, line by line, into objects representing lines, collected within a main object representing the file.
Have a look at the ETL (Extract-Transform-Load) process pattern. This is a modular, scaleable architecture pattern for taking files and turning them into data the program can work with:
Extract - This part of the system is pointed at the filesystem, or other incoming "pipe" for raw data, and its job is to open the file, extract the data into a very basic object format that can be further manipulated, and put those objects into an in-memory "queue" for the Transform step. The goal is to get data from the pipe as fast and efficiently as possible, but you are required at this point to have some knowledge of the data you are working with so that you can effectively encapsulate it for further processing; actually turning the data into the format you really want happens later.
Transform - This part of the system takes the extracted data, and performs the logic that will put that data into a hydrated object from your codebase. This is where, given information from the Extract step about the type of file the data was extracted from, you instantiate a domain object that represents the data model, slice the raw data up into the chunks that will be stored as data members, perform any type conversions (data you get from a file is usually either in string format or in raw bits and must be marshalled or otherwise converted into data types that better represent the concept of the data), and validate that the internal structure of the new object is consistent and meets known business rules. Hydrated, valid objects are placed in an output queue to be processed by the Load step.
Load - This step takes the hydrated, valid business objects from the Transform step and persists them into the data store that is used by your system (such as a SQL database or the program's native flat file format).
Well, the old fashioned way was to use stream access operations and read out the data you wanted. This way you could read/write to pretty much any file.
Serialization simply automates this process based on some contract.
Based on your comment, I'm guessing that your requirement is to read any kind of file without having a contract in the first place.
Let's say you have a raw file with the first byte specifying the length of a string and the next set of bytes representing the string;
For example, 5 | H | e | l | l | o
var stream = File.Open(filename);
var length = stream.ReadByte();
byte[] b = new byte[length];
stream.Read(b, 0, length);
var string = Encoding.ASCII.GetString(b);
Binary I/O is as raw as it gets.
Check MSDN for more.
Below is something I read and was wondering if the statement is true.
Serialization is the process of
converting a data structure or object
into a sequence of bits so that it can
be stored in a file or memory buffer,
or transmitted across a network
connection link to be "resurrected"
later in the same or another computer
environment.[1] When the resulting
series of bits is reread according to
the serialization format, it can be
used to create a semantically
identical clone of the original
object. For many complex objects, such
as those that make extensive use of
references, this process is not
straightforward.
Serialization is just a fancy way of describing what you do when you want a certain data structure, class, etc to be transmitted.
For example, say I have a structure:
struct Color
{
int R, G, B;
};
When you transmit this over a network you don't say send Color. You create a line of bits and send it. I could create an unsigned char* and concatenate R, G, and B and then send these. I just did serialization
Serialization of some kind is required, but this can take many forms. It can be something like dotNET serialization, that is handled by the language, or it can be a custom built format. Maybe a series of bytes where each byte represents some "magic value" that only you and your application understand.
For example, in dotNET I can can create a class with a single string property, mark it as serializable and the dotNET framework takes care of most everything else.
I can also build my own custom format where the first 4 bytes represent the length of the data being sent and all subsequent bytes are characters in a string. But then of course you need to worry about byte ordering, unicode vs ansi encoding, etc etc.
Typically it is easier to make use of whatever framework your language/OS/dev framework uses, but it is not required.
Yes, serialization is the only way to transmit data over the wire. Consider what the purpose of serialization is. You define the way that the class is stored. In memory tho, you have no way to know exactly where each portion of the class is. Especially if you have, for instance, a list, if it's been allocated early but then reallocated, it's likely to be fragmented all over the place, so it's not one contiguous block of memory. How do you send that fragmented class over the line?
For that matter, if you send a List<ComplexType> over the wire, how does it know where each ComplexType begins and ends.
The real problem here is not getting over the wire, the problem is ending up with the same semantic object on the other side of the wire. For properly transporting data between dissimilar systems -- whether via TCP/IP, floppy, or punch card -- the data must be encoded (serialized) into a platform independent representation.
Because of alignment and type-size issues, if you attempted to do a straight binary transfer of your object it would cause Undefined Behavior (to borrow the definition from the C/C++ standards).
For example the size and alignment of the long datatype can differ between architectures, platforms, languages, and even different builds of the same compiler.
Is serialization a must in order to transfer data across the wire?
Literally no.
It is conceivable that you can move data from one address space to another without serializing it. For example, a hypothetical system using distributed virtual memory could move data / objects from one machine to another by sending pages ... without any specific serialization step.
And within a machine, the objects could be transferred by switch pages from one virtual address space to another.
But in practice, the answer is yes. I'm not aware of any mainstream technology that works that way.
For anything more complex than a primitive or a homogeneous run of primitives, yes.
Binary serialization is not the only option. You can also serialize an object as an XML file, for example. Or as a JSON.
I think you're asking the wrong question. Serialization is a concept in computer programming and there are certain requirements which must be satisfied for something to be considered a serialization mechanism.
Any means of preparing data such that it can be transmitted or stored in such a way that another program (including but not limited to another instance of the same program on another system or at another time) can read the data and re-instantiate whatever objects the data represents.
Note I slipped the term "objects" in there. If I write a program that stores a bunch of text in a file; and I later use some other program, or some instance of that first program to read that data ... I haven't really used a "serialization" mechanism. If I write it in such a way that the text is also stored with some state about how it was being manipulated ... that might entail serialization.
The term is used mostly to convey the concept that active combinations of behavior and state are being rendered into a form which can be read by another program/instance and instantiated. Most serialization mechanism are bound to a particular programming language, or virtual machine system (in the sense of a Java VM, a C# VM etc; not in the sense of "VMware" virtual machines). JSON (and YAML) are a notable exception to this. They represents data for which there are reasonably close object classes with reasonably similar semantics such that they can be instantiated in multiple different programming languages in a meaningful way.
It's not that all data transmission or storage entails "serialization" ... is that certain ways of storing and transmitting data can be used for serialization. At very list it must be possible to disambiguated among the types of data that the programming language supports. If it reads: 1 is has to know whether that's text or an integer or a real (equivalent to 1.0) or a bit.
Strictly speaking it isn't the only option; you could put an argument that "remoting" meets the meaning inthe text; here a fake object is created at the receiver that contains no state. All calls (methods, properties etc) are intercepted and only the call and result are transferred. This avoids the need to transfer the object itself, but can get very expensive if overly "chatty" usage is involved (I.e. Lots of calls)as each has the latency of the speed of light (which adds up).
However, "remoting" is now rather out of fashion. Most often, yes: the object will need to be serialised and deserialized in some way (there are lots of options here). The paragraph is then pretty-much correct.
Having a messages as objects and serializing into bytes is a better way of understanding and managing what is transmitted over wire. In the old days protocols and data was much simpler, often, programmers just put bytes into output stream. Common understanding was shared by having well-known and simple specifications.
I would say serialization is needed to store the objects in file for persistence, but dynamically allocated pointers in objects need to be build again when we de-serialize, But the serialization for transfer depends on the physical protocol and the mechanism used, for example if i use UART to transfer data then its serialized bit by bit but if i use parallel port then 8 bits together gets transferred , which is not serialized
Where exactly does serialization comes into the picture? I read about serializtion on the 'net and I have come to know that
it is an interface that if implements in a class, means that it can be automatically be serialized and deserialized by the different serializers.
Give me a good reason why and when would a class needs to be serialized? Suppose once it's serialized, what happens exactly?
Serialization is needed whenever an object needs to be persisted or transmitted beyond the scope of its existence.
Persistence is the ability to save an object somewhere and load it later with the same state. For example:
You might need to store an object instance on disk as part of a file.
You might need to store an object in a database as a blob (binary large object).
Transmission is the ability to send an object outside of its original scope to some receiver. For example:
You might need to transmit an instance of an object to a remote machine.
You might need to transmit an instance to another AppDomain or process on the same machine.
For each of these, there must be some serial bit representation that can be stored, communicated, and then later used to reconstitute the original object. The process of turning an object into this series of bits is called "serialization", while the process of turning the series of bits into the original object is called "deserialization".
The actual representation of the object in serialized form can differ depending on what your goals are. For example, in C#, you have both XML serialization (via the XmlSerializer class) and binary serialization (through use of the BinaryFormatter class). Depending on your needs, you can even write your own custom serializer to do additional work such as compression or encryption. If you need a language- and platform-neutral serialization format, you can try Google's Protocol Buffers which now has support for .NET (I have not used this).
The XML representation mentioned above is good for storing an object in a standard format, but it can be verbose and slow depending on your needs. The binary representation saves on space but isn't as portable across languages and runtimes as XML is. The important point is that the serializer and deserializer must understand each other. This can be a problem when you start introducing backward and forward compatibility and versioning.
An example of potential serialization compatibility issues:
You release version 1.0 of your program which is able to serialize some Foo object to a file.
The user does some action to save his Foo to a file.
You release version 2.0 of your program with an updated Foo.
The user tries to open the version 1.0 file with your version 2.0 program.
This can be troublesome if the version 2.0 Foo has additional properties that the version 1.0 Foo didn't. You have to either explicitly not support this scenario or have some versioning story with your serialization. .NET can do some of this for you. In this case, you might also have the reverse problem: the user might try to open a version 2.0 Foo file with version 1.0 of your program.
I have not used these techniques myself, but .NET 2.0 and later has support for version tolerant serialization to support both forward and backward compatibility:
Tolerance of extraneous or unexpected data. This enables newer versions of the type to send data to older versions.
Tolerance of missing optional data. This enables older versions to send data to newer versions.
Serialization callbacks. This enables intelligent default value setting in cases where data is missing.
For example when you want to send objects over network or storing them into files.
Lets say you're creating a Savegame-format for a video-game. You then could make the class Player and every Enemy serializable. This way it would be easy to save the state of the current objects into a file.
On the other end, when writing a multiplayer-implementation for your game, you could send the Player serialized via network to the other clients, which then could handle these data.
In non-object-oriented languages, one would typically have data stored in memory in a pattern of bytes that would 'make sense' without reference to anything else. For example, a bunch of shapes in a graphics editor might simply have all their points stored consecutively. In such a program, simply storing the contents of all one's arrays to disk might yield a file which, when read back into those arrays would yield the original data.
In object-oriented languages, many objects are stored as references to other objects. Merely storing the contents of in-memory data structures will not be useful, because a reference to object #24601 won't say anything about what that object represents. While an object-oriented system may be able to do a pretty good job figuring out what the in-memory data "mean" and try to convert it automatically to a sensible format, it can't recognize all the distinctions between object references which point to the same object, and those that point to objects which happen to match. It's thus often necessary to help out the system when converting objects to a raw stream of bits.
Not classes, but the specific objects might be serialized to store in some persistent storage or to pass the object to another application/via network.
for example, when you want to send a object to some url, you might decide to send it in xml format. The process of converting from the in-memory object to (in this case) xml, is called serialization. Converting from xml to a in-memory is called de-serialization.