1. Client server programming
Sockets Recap
Sockets
Stream sockets
Datagram sockets
Multicast Sockets (datagram sockets)
08/11/2018
Client server programming

2. Advanced (Stream) Socket Programming
Jin Sa
08/11/2018
Client server programming

3. Client server programming
Outline
Object serialization
Overview of object serialization
Examples of object serialization
Transport objects over stream sockets
08/11/2018
Client server programming

4. Client server programming
Rationale
Compared with socket, Java Remote Method Invocation (RMI) provides a simple way to distribute objects across networks. However, there is a network communication overhead.
Low-level sockets can be used to develop client/server systems, but most Java I/O classes are not object friendly.
Object serialization is the mechanism that allows you to read/write objects to byte streams.
Combine low-level sockets and object serialization to enables us to transport objects over sockets and overcome the overhead incurred in using RMI.
08/11/2018
Client server programming

5. Client server programming
Object I/O
InputStream and OutputStream can be further divided to more specialised I/O streams.
DataInputStream and DataOutputStream enable us to perform I/O for primitive type values and strings.
ObjectInputStream and ObjectOutputStream enable us to perform I/O for objects.
The methods are readObject() and writeObject(…)
08/11/2018
Client server programming

6. Client server programming
Example of Object I/O
TestWriteObject
Create an ObjectOutputStream which associated with an output file
Create a Date object
Write the current state of the date object to the file “test1”
TestReadObject
Create an ObjectInputStream which is associated with an input file
Read the date object from the file
find out the state of the date object when it was written to the file.
Run programs in objectserial package
08/11/2018
Client server programming

7. Client server programming
Object serialization
Not all objects can be written to an output stream. Objects that can be written to an output stream are said to be serializable.
Object serialization is a mechanism that is useful in any program that wants to save the state of objects to a file and later read those objects to reconstruct the state of the program, or to send an object over the network using sockets.
Serializing a class can be easily done by having the class implement the java.io.Serializable interface.
Implementing this interface enables the Java serialization mechanism to automate the process of storing objects.
The Date is serializable. Hence we can store its objects to an output stream
We can define our own class to implement the Serializable interface.
08/11/2018
Client server programming

8. Student record example
Define a StudentRecord class (serialisable)
Define a WriteStudentRecord class that create an instance of StudentRecord, makes some changes to the instance and saves the instance to a file.
Define a ReadStudentRecord class that reads the instance from the file, and displays the information of the instance.
08/11/2018
Client server programming

9. Client server programming
StudentRecord class
public class StudentRecord implements Serializable{
private String name, subject;
private int grade;
public StudentRecord(String n) {
name=n; }
public void setSubject(String s){
subject=s;
public void setGrade(int g){
grade=g;
public String toString(){
return (name + " is doing "+ subject +" and has got "+ grade);
08/11/2018
Client server programming

10. WriteStudentRecord class
Create a StudentRecord object
Set the subject and the grade
Create an instance of an ObjectOutputStream for a file
Write the StudentRecord object to the ObjetOutputStream
08/11/2018
Client server programming

11. Fragment of WriteStudentRecord
StudentRecord s=new StudentRecord("Jin");
s.setSubject("Chinese");
s.setGrade(99);
String fileName="myFile"; …
ObjectOutputStream oos =
new ObjectOutputStream(
new FileOutputStream(fileName));
oos.writeObject(s);
08/11/2018
Client server programming

12. Fragment of ReadStudentRecord class
String fileName="myFile"; …
ObjectInputStream ois=
new ObjectInputStream(
new FileInputStream(fileName));
StudentRecord record =
(StudentRecord)ois.readObject();
System.out.print(record.toString());
Run program in objectserial package
08/11/2018
Client server programming

13. Transporting Objects over Sockets
Now we have seen how to write and read objects to and from I/O streams, let’s see how to transport objects between different processes over stream sockets.
08/11/2018
Client server programming

14. StudentRecord application
RecordServer
StudentClient
Wait for and establish connection
Request to connect
Set up object input and output streams
Set up object input and output streams
Create a student record (for Jin)
Receive a record from the server
Send the record object
Student select the subject, change the record and send to the server
Receive the record from the student
Set the grade, update the record and send back to student
Receive the record from the server
08/11/2018
Client server programming

15. Process for transporting objects
For the server
Create a ServerSocket to listen for connection request
Issue an accept method to accept a connection request, create a stream socket once a connection is established
From the socket, create an object input stream and an object output stream.
To send an object to a client, use the writeObject method for the objectOutputStream
To receive an object, use the readObject method for the ObjectInoutSream.
Note that the objects being transported must be serialisable.
08/11/2018
Client server programming

16. Process for transporting objects
For the client
Make a connection request by creating a socket
Set up the object input and output streams connected to the server.
To send an object to the server, use the writeObject method for the objectOutputStream
To receive an object, use the readObject method for the ObjectInoutSream.
Note that the objects being transported must be serialisable.
08/11/2018
Client server programming

17. Client server programming
files
2006/7 code/clientserver2/sending objects
Or in two separate projects:
ClientProject
ServerProject
08/11/2018
Client server programming

18. Fragment of RecordsServer
ServerSocket dateServer = new ServerSocket(3000); …
while(true) {
Socket client = dateServer.accept();
ois =
new ObjectInputStream(client.getInputStream());
oos =
new ObjectOutputStream(client.getOutputStream());
StudentRecord record1= new StudentRecord("Jin");
oos.writeObject(record1);
record1=(StudentRecord)ois.readObject();
record1.setGrade(90); }
08/11/2018
Client server programming

19. Fragment of StudentClient
socket = new Socket("localhost",3000);
oos = new ObjectOutputStream(socket.getOutputStream());
ois = new ObjectInputStream(socket.getInputStream());
StudentRecord record =
(StudentRecord) ois.readObject();
record.setSubject("Java");
oos.writeObject(record);
record=(StudentRecord)ois.readObject();
System.out.print(record.toString());
08/11/2018
Client server programming

20. Client server programming
Summary
Object serialisation
Transporting objects using sockets
08/11/2018
Client server programming