NETWORKING - Introduction to Java Programming: Comprehensive Version - page 1142

Note
The Socket constructor throws a java.net.UnknownHostException if the host
cannot be found.

UnknownHostException

31.2.3 Data Transmission through Sockets
After the server accepts the connection, communication between the server and the client is
conducted in the same way as for I/O streams. The statements needed to create the streams and
to exchange data between them are shown in Figure 31.2.

Server Client

int port = 8000; int port = 8000;

DataInputStream in;
DataOutputStream out;
ServerSocket server;
Socket socket;

String host = "localhost"
DataInputStream in;
DataOutputStream out;
Socket socket;

Connection
Request

server = new ServerSocket(port);
socket = server.accept();
in = new DataInputStream
(socket.getInputStream());
out = new DataOutStream
(socket.getOutputStream());
System.out.println(in.readDouble());
out.writeDouble(aNumber);

socket = new Socket(host, port);
in = new DataInputStream
(socket.getInputStream());
out = new DataOutputStream
(socket.getOutputStream());

I/O
Streams

out.writeDouble(aNumber);

System.out.println(in.readDouble());

F IGURE 31.2

The server and client exchange data through I/O streams on top of the socket.

To get an input stream and an output stream, use the getInputStream() and
getOutputStream() methods on a socket object. For example, the following statements
create an InputStream stream called input and an OutputStream stream called output
from a socket:

InputStream input = socket.getInputStream();
OutputStream output = socket.getOutputStream();

The InputStream and OutputStream streams are used to read or write bytes. You can
use DataInputStream , DataOutputStream , BufferedReader , and PrintWriter to
wrap on the InputStream and OutputStream to read or write data, such as int , double ,
or String . The following statements, for instance, create the DataInputStream stream
input and the DataOutput stream output to read and write primitive data values:

DataInputStream input = new DataInputStream
(socket.getInputStream());
DataOutputStream output = new DataOutputStream
(socket.getOutputStream());

The server can use input.readDouble() to receive a double value from the client and
output.writeDouble(d) to send the double value d to the client.

Tip
Recall that binary I/O is more efficient than text I/O because text I/O requires encoding
and decoding. Therefore, it is better to use binary I/O for transmitting data between a
server and a client to improve performance.