Java Networking

ADVANCE JAVA
Classified e-Material 2
NETWORK PROGRAMMING
java.net
PACKAGE

ADVANCE JAVA
Author Profile
 Ankit Desai
 Ph.D. Scholar, IET, Ahmedabad University
 Education: M. Tech. (C.E.), B. E. (I. T.)
 Experience: 8 years (Academic and Research)
 Research Interest: IoT, Big Data Analytics, Machine
Learning, Data Mining, Algorithms.

ADVANCE JAVA
InetAddress CLASS
 The Inetaddress class provides you with a limited
interface to DNS for doing both forward and
reverse internet address lookups
 An InetAddress class method corresponds to a DNS
request

ADVANCE JAVA
InetAddress CLASS
 No public constructor
 Static methods:
 static InetAddress[] getAllByName (String host)
 Static method used to retrieve all the addresses for the
host name passed as a parameter.
 static InetAddress getByAddress(byte[] addr)
 Returns an InetAddress object given the raw IP address .
 static InetAddress getByAddress (String host,
byte[] addr)
 Create an InetAddress based on the provided host name
and IP address No name service is checked for the validity
of the address.

ADVANCE JAVA
 static InetAddress getByName(String)
 Static method used to retrieve the address for the host
name passed as the parameter.
 static InetAddress getLocalHost( )
 Static method used to retrieve the address for the
current, or local, host.

ADVANCE JAVA
InetAddress Class
 Additional “getter” methods
 byte[ ] getAddress()
 Returns the IP address.
 String getHostAddress()
 Returns the IP address as a string.
 String getHostName()
 Returns the host name.

ADVANCE JAVA
InetAddress Examples
try
{
InetAddress host = InetAddress.getLocalHost();
System.out.println(host.getHostName());
byte ip[] = host.getAddress();
for (int i=0; i<ip.length; i++) {
if (i > 0) {
System.out.print(".");
}
System.out.print(ip[i] & 0xff);
}
}
catch (UnknownHostException e)
{ // Exception handling here. }

ADVANCE JAVA
TCP Sockets
 Once a TCP socket connection is made, a virtual
stream is in place. Java’s IO model is that of a stream,
therefore the models are consistent; all you need to do
connect a TCP socket to a stream and read and write
the streams.

ADVANCE JAVA
JAVA TCP Sockets
 In Package java.net
 java.net.Socket
 Implements client sockets (also called just “sockets”).
 An endpoint for communication between two
machines.
 Constructor and Methods
 Socket(String host, int port): Creates a stream socket
and connects it to the specified port number on the
named host.
 InputStream getInputStream()
 OutputStream getOutputStream()
 close()

ADVANCE JAVA
 java.net.ServerSocket
 Implements server sockets.
 Waits for requests to come in over the network.
 Performs some operation based on the request.
 Constructor and Methods
 ServerSocket(int port)
 Socket Accept(): Listens for a connection to be made to this
socket and accepts it. This method blocks until a connection
is made.

ADVANCE JAVA
Socket Class - TCP Client sockets
 Socket(String ip, int port)
 Creates a streaming socket and binds it to the host and
port specified as parameters.
 Socket(String ip, int port, boolean TCPorUDP)
 Creates a socket and binds it to the host and port
specified as parameters. The last parameter is used to
indicate whether the socket should be a stream or
datagram socket.
 Socket(InetAddress ia, int port)
 Creates a streaming socket connected to the specified
host and port.
 Socket(InetAddress ia, int port, boolean TCPorUDP)
 Creates a socket connected to the specified host and
port. The last parameter specifies whether the socket
should be a stream or datagram socket.

ADVANCE JAVA
Client Sockets (Methods)
 InetAddress getInetAddress( )
 Returns the address to which the socket is connected
 int getPort( )
 Returns the port number on the remote host for this
socket
 InetAddress getLocalAddress( )
 Gets the local address to which the socket is bound.
 int getLocalPort( )
 Returns the port number on the local host for this
socket.
 InputStream getInputStream( )
 Returns an input stream for the socket.
 OutputStream getOutputStream( )
 Returns an output stream for the socket.
 void close()
 Closes the socket.

ADVANCE JAVA
 int GetSoLinger()
 void setSoLinger(boolean on, int linger)
 This option sets how long a socket is remain open
after a close() method has been invoked and data
remains to be sent over the socket
 public int getSoTimeout()
 public void setSoTimeout(int timeout)
 this option set to a non-zero timeout, a read() call on
the InputStream associated with this Socket will block
for only this amount of time

ADVANCE JAVA
 public void setTcpNoDelay(boolean on)
 public boolean getTcpNoDelay()
 Option is used to specify Nagle’s algorithm should
be used to buffer data that is sent over a socket
connection.

ADVANCE JAVA
ServerSocket class- Constructors
 public ServerSocket(int port) throws IOException
 Creates a server socket, bound to the specified port.
 public ServerSocket(int port, int backlog) throws
IOException
 Creates a server socket and binds it to the specified local
port number, with the specified backlog.
 public ServerSocket(int port, int backlog, InetAddress
networkInterface) throws IOException
 Create a server with the specified port, listen backlog,
and local IP address to bind to.

ADVANCE JAVA
ServerSocket class- Methods
 public Socket accept() throws IOException
 Listens for a connection to be made to this socket and
accepts it. The method blocks until a connection is
made
 public void close() throws IOException
 Closes this socket. Any thread currently blocked in
accept() will throw a SocketException
 public InetAddress getInetAddress()
 Returns the local address of this server socket
 public void bind(SocketAddress endpoint) throws
IOException
 Binds the ServerSocket to a specific address (IP
address and port number)

ADVANCE JAVA
 public int getLocalPort()
 Returns the port on which this socket is listening.
 public SocketAddress getLocalSocketAddress()
 Returns the address of the endpoint this socket is bound
to, or null if it is not bound yet.
 protected final void implAccept(Socket s) throws
IOException
 Subclasses of ServerSocket use this method to override
accept() to return their own subclass of socket.
 public boolean isBound()
 Returns the binding state of the ServerSocket.
 public boolean isClosed()
 Returns the closed state of the ServerSocket

ADVANCE JAVA
 public void setSoTimeout(int timeout) throws
SocketException
 Enable/disable SO_TIMEOUT with the specified timeout,
in milliseconds. With this option set to a non-zero
timeout, a call to accept() for this ServerSocket will
block for only this amount of time. If the timeout
expires, a java.net.SocketTimeoutException is
raised, though the ServerSocket is still valid
 public int getSoTimeout() throws IOException
 Retrive setting for SO_TIMEOUT. 0 returns implies that
the option is disabled
 public void setReuseAddress(boolean on) throws
SocketException
 Enable/disable the SO_REUSEADDR socket option

ADVANCE JAVA
 public boolean getReuseAddress() throws
SocketException
 Tests if SO_REUSEADDR is enabled

ADVANCE JAVA
Implementing a Server
1. Open the Server Socket:
ServerSocket server;
DataOutputStream os;
DataInputStream is;
server = new ServerSocket( PORT );
2. Wait for the Client Request:
Socket client = server.accept();
3. Create I/O streams for communicating to the client
is = new DataInputStream( client.getInputStream());
os = new DataOutputStream( client.getOutputStream());
4. Perform communication with client
Receive from client: String line = is.readLine();
Send to client: os.writeBytes("Hellon");
5. Close sockets: client.close();

ADVANCE JAVA
For multithreaded server:
while(true) {
i. wait for client requests (step 2 above)
ii. create a thread with “client” socket as
parameter (the thread creates streams (as in
step (3) and does communication as stated in
(4). Remove thread once service is provided.
}

ADVANCE JAVA
Implementing a Client
1. Create a Socket Object:
client = new Socket( server, port_id );
2. Create I/O streams for communicating with the server:
is = new DataInputStream(client.getInputStream() );
os = new DataOutputStream(client.getOutputStream() );
3. Perform I/O or communication with the server:
Receive data from the server:
String line = is.readLine();
Send data to the server:
os.writeBytes("Hellon");
4. Close the socket when done:
client.close();

ADVANCE JAVA
TCPClient.java
import java.io.*;
import java.net.*;
class TCPClient {
public static void main(String argv[]) throws Exception
{
String sentence;
String modifiedSentence;
BufferedReader inFrom = new BufferedReader(new InputStreamReader(argv[0]));
Socket clientSock = new Socket("hostname", 6789);
DataOutputStream outTo = new DataOutputStream(clientSock.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new
InputStreamReader(clientSocket.getInputStream()));
sentence = inFrom.readLine();
outToServer.writeBytes(sentence + 'n');
modifiedSentence = inFrom.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSock.close();
}
}

ADVANCE JAVA
TCPServer.java
import java.io.*;
import java.net.*;
class TCPServer {
public static void main(String argv[]) throws Exception
{
String clientSentence;
String capitalizedSentence;
ServerSocket welcomeSocket = new ServerSocket(6789);
while(true) {
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new
InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient =
new DataOutputStream(connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
capitalizedSentence = clientSentence.toUpperCase() + 'n';
outToClient.writeBytes(capitalizedSentence);
} } }

ADVANCE JAVA
UDP Sockets
 Since UDP is a connectionless protocol; there is no
virtual stream between the hosts so streams are not
used for IO.
 UDP applications are not thought of in terms of
clients and servers, but rather in terms of senders
and receivers.
 For conversational applications both ends (sender
and receiver) will be changing states from sender to
receiver and back again
 Many UDP based applications are simple send a
request then receive the data (sender’s perspective),
like a DNS request. The receiver’s perspective is to
‘listen’ for a request, send the response, listen for
more requests.

ADVANCE JAVA
DatagramPacket Class
 UDP sockets send and receive Datagrams
 Constructors: two for receiving, four for sending
 DatagramPacket( byte[ ] buff , int len)
 Constructs a DatagramPacket for receiving packets of
length len.
 DatagramPacket(byte[] buf, int off, int len)
 Constructs a DatagramPacket for receiving packets of
length len, specifying an offset of off bytes into the buffer.
 DatagramPacket((byte[] buf, int len, InetAddress addr,
int port)
 Constructs a datagram packet for sending packets of
length len to the specified port number on the specified
host.

ADVANCE JAVA
 DatagramPacket(byte[] buf, int off, int len,
SocketAddress addr)
length len with offset off to the specified port number
on the specified host.
 DatagramPacker(byte[] buf, int off, int len,
InetAddress addr, int port)
length len with offset off to the specified port number
on the specified host.

ADVANCE JAVA
DatagramPacket Class- Methods
 public InetAddress getAddress()
 Returns the IP address of the machine to which this
datagram is being sent or from which the datagram
was received.
 public int getPort()
 Returns the port number on the remote host to which
this datagram is being sent or from which the
datagram was received.
 public byte[] getData()
 Returns the data buffer. The data received or the data
to be sent starts from the offset in the buffer, and runs
for length long.
 public int getOffset()
 Returns the offset of the data to be sent or the offset
of the data received.

ADVANCE JAVA
 public int getLength()
 Returns the length of the data to be sent or the
length of the data received.
 public void setData(byte[] buf, int offset, int length)
 Set the data buffer for this packet. This sets the
data, length and offset of the packet.
 public void setAddress(InetAddress iaddr)
 Sets the IP address of the machine to which this
datagram is being sent.
 public void setPort(int iport)
 Sets the port number on the remote host to which
this datagram is being sent.

ADVANCE JAVA
 public void
setSocketAddress(SocketAddress address)
 Sets the SocketAddress (usually IP address + port
number) of the remote host to which this datagram
is being sent.
 public SocketAddress getSocketAddress()
 Gets the SocketAddress (usually IP address + port
number) of the remote host that this packet is
being sent to or is coming from.
 public void setData(byte[] buf)
 Set the data buffer for this packet. With the offset
of this DatagramPacket set to 0, and the length set
to the length of buf.

ADVANCE JAVA
 public void setLength(int length)
 Set the length for this packet. The length of the
packet is the number of bytes from the packet's data
buffer that will be sent, or the number of bytes of the
packet's data buffer that will be used for receiving
data. The length must be lesser or equal to the offset
plus the length of the packet's buffer.

ADVANCE JAVA
DatagramSocket Class – UDP Sockets
 Constructors
 DatagramSocket()
 Constructs a datagram socket and binds it to any available port
on the local host.
 DatagramSocket(DatagramSocketImpl impl)
 Creates an unbound datagram socket with the specified
DatagramSocketImpl.
 DatagramSocket(int port)
 Constructs a datagram socket and binds it to the specified port
on the local host.
 DatagramSocket(int port, InetAddress iaddr)
 Creates a datagram socket, bound to the specified local
address.
 DatagramSocket(SocketAddress bindaddr)
 Creates a datagram socket, bound to the specified local socket
address.

ADVANCE JAVA
DatagramSocket Class –Methods
 public void bind(SocketAddress addr) throws
SocketException
 Binds this DatagramSocket to a specific address &
port.
 public void connect(InetAddress address, int port)
 Connects the socket to a remote address for this
socket.
 public void connect(SocketAddress addr) throws
SocketException
 Connects this socket to a remote socket address (IP
address + port number).
 public void disconnect()
 Disconnects the socket. This does nothing if the
socket is not connected.

ADVANCE JAVA
 public boolean isBound()
 Returns the binding state of the socket.
 public boolean isConnected()
 Returns the connection state of the socket.
 public InetAddress getInetAddress()
 Returns the address to which this socket is
connected. Returns null if the socket is not
connected.
 public int getPort()
 Returns the port for this socket. Returns -1 if the
socket is not connected.

ADVANCE JAVA
 public SocketAddress getRemoteSocketAddress()
 Returns the address of the endpoint this socket is
connected to, or null if it is unconnected.
 public SocketAddress getLocalSocketAddress()
 Returns the address of the endpoint this socket is
bound to, or null if it is not bound yet.
 public void send(DatagramPacket p) throws
IOException
 Sends a datagram packet from this socket.
 public void receive(DatagramPacket p) throws
IOException
 Receives a datagram packet from this socket.

ADVANCE JAVA
 public InetAddress getLocalAddress()
 Gets the local address to which the socket is bound
 public int getLocalPort()
 Returns the port number on the local host to which
this socket is bound
 public void setSoTimeout(int timeout) throws
SocketException
 Enable/disable SO_TIMEOUT with the specified
timeout, in milliseconds
 public int getSoTimeout() throws SocketException
 Retrive setting for SO_TIMEOUT. 0 returns implies
that the option is disabled

ADVANCE JAVA
 public void setSendBufferSize(int size) throws
SocketException
 Sets the SO_SNDBUF option to the specified value for
this DatagramSocket
 public int getSendBufferSize() throws
SocketException
 Get value of the SO_SNDBUF option for this
DatagramSocket, that is the buffer size used by the
platform for output on this DatagramSocket
 public void setReceiveBufferSize(int size) throws
SocketException
 Sets the SO_RCVBUF option to the specified value for
this DatagramSocket
 public int getReceiveBufferSize() throws
SocketException
 Get value of the SO_RCVBUF option for this
DatagramSocket, that is the buffer size used by the
platform for input on this DatagramSocket

ADVANCE JAVA
Multicast Example
DatagramSocket socket = new DatagramSocket();
byte[] b = new byte[DGRAM_LENGTH];
DatagramPacket dgram;
dgram = new DatagramPacket(b, b.length,
InetAddress.getByName(MCAST_ADDR), DEST_PORT);
System.err.println("Sending " + b.length + " bytes to " +
dgram.getAddress() + ':' + dgram.getPort());
while(true) {
System.err.print(".");
socket.send(dgram);
Thread.sleep(1000);
}

ADVANCE JAVA
Multicast Example
byte[] b = new byte[BUFFER_LENGTH];
DatagramPacket dgram = new DatagramPacket(b,
b.length);
MulticastSocket socket = new
MulticastSocket(DEST_PORT); // must bind receive side
socket.joinGroup(InetAddress.getByName(MCAST_ADDR));
while(true) {
socket.receive(dgram); // blocks until a datagram is
received System.err.println("Received " +
dgram.getLength() + " bytes from " +
dgram.getAddress());
dgram.setLength(b.length); // must reset length field!
}

ADVANCE JAVA
URL Class
 Represents a Uniform Resource Locator, a pointer
to a "resource" on the World Wide Web.
 Consist of a protocol, host name, path and file
name.
 Example:
 http://archive.ncsa.uiuc.edu/SDG/Software/Mosaic/Demo/
 It may contains either relative or absolute path of
file.

ADVANCE JAVA
URL Class - Constructors
 URL(String spec)
 Creates a URL object from the String representation
 URL(String protocol, String host, int port, String file)
 Creates a URL object from the specified protocol, host,
port number, and file
 URL(String protocol, String host, int port, String file,
URLStreamHandler handler)
 Creates a URL object from the specified protocol, host,
port number, file, and handler.

ADVANCE JAVA
 URL(String protocol, String host, String file)
 Creates a URL from the specified protocol name, host
name, and file name
 URL(URL context, String spec)
 Creates a URL by parsing the given spec within a
specified context
 URL(URL context, String spec,
URLStreamHandler handler)
 Creates a URL by parsing the given spec with the
specified handler within a specified context.

ADVANCE JAVA
URL Class - Methods
 Object getContent()
 Gets the contents of this URL.
 Int getDefaultPort()
 Gets the default port number of the protocol
associated with this URL.
 String getFile()
 Gets the file name of this URL
 String getHost()
 Gets the host name of this URL, if applicable.
 String getPath()
 Gets the path part of this URL.

ADVANCE JAVA
URL Class - Methods
 int getPort()
 Gets the port number of this URL.
 String getProtocol()
 Gets the protocol name of this URL.
 String getQuery()
 Gets the query part of this URL
 InputStream openStream()
 Opens a connection to this URL and returns an
InputStream for reading from that connection.
 protected void set(String protocol, String host,
int port, String file, String ref)
 Sets the fields of the URL.
 protected void set(String protocol, String host,
int port, String authority, String userInfo, String path,
String query, String ref)
 Sets the specified 8 fields of the URL.

ADVANCE JAVA
URL Class - example
import java.lang.System;
import java.net.URL;
import java.net.MalformedURLException;
import java.io.*;
public class GetURLApp {
public static void main(String args[]){
try{ if(args.length!=1) error("Usage: java GetURLApp
URL");
System.out.println("Fetching URL: "+args[0]);
URL url = new URL(args[0]);
BufferedReader inStream = new BufferedReader( new
InputStreamReader(url.openStream()));

ADVANCE JAVA
String line;
while ((line = inStream.readLine())!= null)
{ System.out.println(line); }
inStream.close();
}catch (MalformedURLException ex){ error("Bad
URL");
}catch (IOException ex){ error("IOException
occurred."); } }
public static void error(String s){
System.out.println(s);
System.exit(1);
}
}

ADVANCE JAVA
URLConnection and HTTPURLConnection class
 URLConnection
 It is an abstract class.
 It gives information about the web object,
connection to web object.
 It provides the way to interact with the web object.
 Example
 URL url = new URL ("http://www.google.com/");
 InputStream inputStream = url.openStream ();
 OR
 URL url = new URL ("http://www.google.com/");
 URLConnection urlConnection = url.openConnection
();
 InputStream inputStream = urlConnection.getInput
Stream ();

ADVANCE JAVA
URLConnection
 The URL is constructed.
 The URL’s openConnection() method creates the
URLConnection object.
 The parameters for the connection and the
request properties that the client sends to the
server are set up.
 The connect() method makes the connection to
the server. (optional)
 The response header information is read using
getHeaderField().

ADVANCE JAVA
Header Viewer Example
import java.net.URLConnection;
import java.util.Date;
public class MainClass {
public static void main(String args[]) throws Excep
tion {
URL u = new URL("http://www.java2s.com");
URLConnection uc = u.openConnection();
System.out.println("Content-
type: " + uc.getContentType());
encoding: " + uc.getContentEncoding());
System.out.println("Date: " + new Date(uc.getD
ate()));

ADVANCE JAVA
System.out.println("Last modified: " + new Date(uc.g
etLastModified()));
System.out.println("Expiration date: " + new Date(
uc.getExpiration()));
length: " + uc.getContentLength());
}}
Output:
Content-type: text/html
Content-encoding: null
Date: Thu May 24 18:41:00 PDT 2007
Last modified: Fri May 18 08:20:08 PDT 2007
Expiration date: Wed Dec 31 16:00:00 PST 1969
Content-length: 345648

ADVANCE JAVA
Writing to a Web server
import java.io.PrintWriter;
import java.net.URLConnection;
public class MainClass {
public static void main(String[] a)throws Exception
{
URL url = new URL("http://www.yourdomain.com
/form.jsp");
URLConnection connection = url.openConnection()
;
connection.setDoOutput(true);
PrintWriter out = new PrintWriter(connection.getO
utputStream());
out.println("firstName=Joe");
out.println("lastName=Average");
out.close();
}
}

ADVANCE JAVA
Classified e-Material
©Copyrights Charotar Institute of 53
URLEncoder class
 Alphanumeric ASCII characters (a-z, A-Z, and 0-9)
and the $-_.!*'(), punctuation symbols are left
unchanged.
 The space character is converted into a plus sign
(+).
 Other characters (e.g. &, =, ^, #, %, ^, {, and so
on) are translated into a percent sign followed by
the two hexadecimal digits corresponding to their
numeric value.
 Example:
 The comma is ASCII character 44 (decimal) or 2C
(hex). Therefore if the comma appears as part of a
URL it is encoded as %2C.
 The query string "Author=Sadie, Julie&Title=Women
Composers" is encoded as: Author=Sadie
%2C+Julie&Title=Women+Composers

ADVANCE JAVA
URLEncoder methods
 URLEncoder.encode(String s)
 URLEncoder.decode(String s)

ADVANCE JAVA
 Example
 String qs = "Author=Sadie, Julie&Title=Women
Composers"; String eqs = URLEncoder.encode(qs);
System.out.println(eqs);
 Prints:
 Author%3dSadie%2c+Julie%26Title
%3dWomen+Composers
 String eqs = "Author=" +
URLEncoder.encode("Sadie, Julie");
 eqs += "&";
 eqs += "Title=";
 eqs += URLEncoder.encode("Women Composers");
 Prints:
 Author=Sadie%2c+Julie&Title=Women+Composers

ADVANCE JAVA
MIME
 MIME is an acronym for "Multipurpose Internet
Mail Extensions".
 An Internet standard defined in RFCs 2045
through 2049
 Originally intended for use with email messages,
but has been been adopted for use in HTTP.

ADVANCE JAVA
Browser Request MIME Header
 When the browser sends a request to a web
server, it also sends a MIME header.
 MIME headers contain name-value pairs,
essentially a name followed by a colon and a
space, followed by a value.
 Connection: Keep-Alive
 User-Agent: Mozilla/3.01 (Macintosh; I; PPC)
 Host: www.digitalthink.com:80
 Accept: image/gif, image/x-xbitmap,
image/jpeg, image/pjpeg, */*

ADVANCE JAVA
Server Response MIME Header
 When a web server responds to a web browser it
sends a response message and a MIME header
along with the response that looks something like
this:
 HTTP/1.0 200 OK
 Server: Netscape-Enterprise/2.01
 Date: Sat, 02 Aug 1997 07:52:46 GMT
 Accept-ranges: bytes
 Last-modified: Tue, 29 Jul 1997 15:06:46 GMT
 Content-length: 2810
 Content-type: text/html

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Java Networking