This document discusses network programming in Java. It shows how to get the local host address and address of google.com. It defines a server as a program that listens on a TCP port for connections and a client as a program that initiates connections. It demonstrates how to create a server socket to listen on a port and how a client socket can connect to an IP address and port. It also discusses Java I/O streams for input and output and how to handle files in Java including checking if a directory exists, creating it if not, opening output streams to write to files, and approaches for reading from files.

1. Network Programming
with Java

2. public static void main(String[] args) throws
UnknownHostException {
InetAddress localAddress = InetAddress.getLocalHost();
System.out.println(localAddress.getHostAddress());
}
public static void main(String[] args) throws
UnknownHostException {
InetAddress googleAddress =
InetAddress.getByName("www.google.com");
System.out.println(googleAddress.getHostAddress());
}

3. TCP/IP Server: That(a program or a process) listens to a TCP
port.
Client: What (a program or a process) initiates the connection
Server is represented by java.net.ServerSocket
Client is represented by java.net.Socket
int portNumber = 7896; // TCP port Number
ServerSocket server = new ServerSocket(portNumber);//
listen on port
Socket socket = server.accept(); // Blocks until
connection made
String destIP = "172.17.20.123"; // Target Host IPv4 Address
int portNumber = 7896; // TCP port Number
Socket socket = new Socket(destIP, portNumber);// connect

4. Stay & while connected…
Server Client
Wait for
connection
Server’s Output/ Client’s Input
Client’s Output/ Server’s Input

5. Java I/O
Some important OutputStream child:
 DataOutputStream
FileOutputStream
ByteArrayOutputStream

6. Java I/O
Some important InputStream child:
DataInputStream
FileInputStream
ByteArrayInputStream
Read an input integer Example

7. File Handling
if(false==dir.exists() || false==dir.isDirectory()){
dir.mkdirs();
}

8. File Handling
5. Open an OutputStream to the file:
6. Write the raw bytes to the OutputStream, flush and close it

9. Write to a File : Second approach
DataOutputStream provides a wrapper over an OutputStream to
write primitive data types, not just byte[]

10. Read from a File
Read byte-by-byte
Read Bytes chunk-wise : Faster approach