Serialization question I haven't seen in this forum

[Vonique Leary]

I understand the concept of serialization and that it is used to transfer files over a network, but I'm a little confused about how often it is used. Aren't all or most java files transferred over a network? I mean if you are accessing a java program while surfing the internet or while playing an online game, aren't those files being transferred over a network? What other ways is a java program accessed if not over a network? I know that there are some applications that run on one's computer but I thought java was mainly an internet language.

[Winston Gutkowski]

Vonique Leary wrote:I understand the concept of serialization and that it is used to transfer files over a network, but I'm a little confused about how often it is used. Aren't all or most java files transferred over a network?

Actually, in that context it's for transferring objects over a network; nothing to do with files.

All serialization is is a way of converting a Java object to a form that can be reconstituted at a later date, or on a different machine (with several caveats). This is called 'persistence', and it says nothing about whether it's stored in a file, a stream, or simply in a database.

I mean if you are accessing a java program while surfing the internet or while playing an online game, aren't those files being transferred over a network? What other ways is a java program accessed if not over a network?

Any way you can access any other program. But just for one: as a local program that runs on your desktop.

I know that there are some applications that run on one's computer but I thought java was mainly an internet language.

Then I suspect you've been blinded by the hype. What Java does have is several features that make it very useful for Web-based applications - not least, a very mature set of libraries and 3rd party products for doing just that - but otherwise, it's no different from any other language.

Winston

[Vonique Leary]

So, do most java programs that are accessed over a network use serialization or are there other ways to persist objects?

Thanks,
Vonique

[Ulf Dittmer]

Most network-aware programs probably use sockets directly. Java object serialization is tricky - it only works if you have a JVM on both sides of the connection, and you generally also need those two JVMs to be of the same version, otherwise serialization does not work. (At least the binary serialization used by Object[In|Out]putStream. The XML serialization of Javabeans offered by the java.beans.XML[En|De]coder classes is more resilient.)

[Campbell Ritchie]

Nice to see you again, Vonique.

[Winston Gutkowski]

Vonique Leary wrote:or are there other ways to persist objects?

Well, it really depends on what you mean by 'persist objects'.

Databases have been persisting data in structured form for decades; and there are excellent tools like Hibernate around, that allow you to create Java objects from table data without a lot of the usual translation code. There are even "object" databases around, but I'm not up on the latest. Last I heard they were still pretty slow compared to regular RDBMS's, and development seemed to be a bit sporadic; but I could be completely out-of-date now.

And even an RDBMS can store a Blob, which is really all a serialized object is; the question comes more in how you key it.

And then there are all sorts of XML-based formats like Ulf said. I don't know if SOAP is still used much these days, but it was one of the first of those types of protocol.

Winston

[Vonique Leary]

Thanks everyone, for your replies. It's a lot clearer now but it makes me realize just how much I don't know about networking, etc. Well, from what I have read on this forum, serialization is not on the test, so I am going to limit my knowledge about it to what I have already learned.

Nice to see you too, Campbell!

Von

[Jayesh A Lalwani]

Most Java programs that "run" over the internet are usually servlets that convert the output to HTML/Javascript and send it back to a web browser. The web browser renders the HTML/javascript on the user's sccreen. One way of looking at this is that the servlet is converting the result into user-friendly HTML, and HTML is the protocol used to "serialize" the result object. This is not really what Java considers as serialization

Some Java programs run as Java applets inside the client's browser. In this case, the server sends the Java class to the browser, and the browser executes the Java class in an embedded JVM. No objects are being serialized here

In some rare cases, Java applications/applets that are running on the client make a socket connection back to the server and communicate to the server using serialized objects. I don't think any serious application does this anymore.

[Vonique Leary]

Thanks for that explanation Jayesh. That really helps to clear up why the only place I've ever seen serialization examples is in the prep book for the test. Things make so much more sense to me now!

Vonique