1. Java Serialization
B.Ramamurthy
11/8/2018
B.Ramamurthy

2. Introduction
The capability to store and retrieve Java objects is essential to building persistence and streaming into application.
In this lecture we will discuss details about Serialization and saving and restoring objects in files.
11/8/2018
B.Ramamurthy

3. Topics for Discussion Object Serialization Writing to an Object Stream
Reading from an Object Stream
Selective Serialization
Exception Handling
Example
11/8/2018
B.Ramamurthy

4. Persistence
The values of the data structures in a program are lost when the program terminates.
If you want the data to exist after program termination you need to store it in a file or in a database.
We will look at file input/output in this discussion.
11/8/2018
B.Ramamurthy

5. Object Serialization
Key to storing and retrieving objects is representing the “state” of the objects in a serialized form sufficient to reconstruct the objects.
Object <===>byte stream, other data to help in reconstruction
Converting an object into an organized byte form for storage, streaming etc.
11/8/2018
B.Ramamurthy

6. How to use Serialization?
1. import java.io.*;
2. Implement java.io.Serialization interface.
3. Use writeObject and readObject methods whose header are as given below:
void writeObject (Object obj) throws IOException;
Object readObject() thorws ClassNotFoundException, IOException;
11/8/2018
B.Ramamurthy

7. Writing to an Object Stream
// serilaize various objects into a file
FileOutputStream f = new FileOutputStream(“tmp”);
ObjectOutputStream s = new ObjectOutputStream(f);
s.writeObject(“Today”);
s.writeObject(new Date());
Theater t = new Theater(4,6,10);
//4 shows, 6 rows, 10 cols
s.writeObject(t);
11/8/2018
B.Ramamurthy

8. Reading from an Object Stream
// Deserialize a objects from a file
FileInputStream inf = new FileInputStream(“tmp”);
ObjectInputStream s1 = new ObjectInputStream(inf);
//read the Object and cast to retrieve the
// actual object
String = (String)s1.readObject();
Data date = (Date)s1.readObject();
11/8/2018
B.Ramamurthy

9. Exception Handling
When ever you deal with IO you need make sure the file creation was successful accessing the files.
So enclose creation of file object and stream object within try and catch.
See Lab4 for example.
11/8/2018
B.Ramamurthy

10. Example try {… } catch(Exception ex) { ex.printStackTrace();
// print the exception stack details
11/8/2018
B.Ramamurthy