advance java online trainings Free Demos for beggener-low fee

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Advanced Java Introducing From RVH Technologies
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Networking

• Using the networking capabilities provided in the
  Java environment is quite easy
• We will see how to use Sockets

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What Is a Socket?

• A socket is one endpoint of a two-way
  communication link between two programs
  running on the network.
• A socket is bound to a port number so that the
  TCP layer can identify the application that data
  is destined to be sent.

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How do Sockets work?

• A server runs on a specific computer and has a
  socket that is bound to a specific port number.

• Client knows the hostname and port of server and
  tries to make a connection request

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Connection established

• If the server accepts the connection it gets a
  new socket bound to a different port.
• It needs a new socket (and consequently a
  different port number) so that it can continue to
  listen to the original socket

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How does Java support Sockets

• The java.net package provides a class, Socket,
  that implements one side of a two-way connection
  between your Java program and another program on
  the network
• It also includes the ServerSocket class, which
  implements a socket that servers can use to
  listen for and accept connections to client

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Establish the Socket connection

Output
Port
Host
try echoSocket new Socket(avatar ",
7777) out new PrintWriter(echoSocket.getOutp
utStream(), true) in new
BufferedReader(new
InputStreamReader(echoSocket.getInputStream()))
catch
Input
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Need to Catch Exceptions
catch (UnknownHostException e)
System.err.println("Don't know about host
avatar.") System.exit(1) catch
(IOException e) System.err.println("Couldn
't get I/O for "
"the connection to avatar.")
System.exit(1)
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Simple Socket Example
Set up a mechanism to read from standard input
BufferedReader stdIn new
BufferedReader(
new InputStreamReader(System.in))
String userInput
while ((userInput stdIn.readLine()) ! null)
out.println(userInput)
System.out.println("echo "
in.readLine())
Read from standard input
Write to Server
Output whats read back from Server
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Close up Shop on Client side
out.close( ) in.close( ) stdIn.close(
) echoSocket.close( )
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Server

• A server must open a SeverSocket
• ServerSocket server new ServerSocket( 7777 )
• Call accept on that socket creating a new socket
• Socket socket server.accept()
• Socket acts as socket from client

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If a socket is a pipe

• We could conceptualize this like so

Ports
Client
Server
The things flowing through the Plumbing
The Socket Plumbing
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Objects flow through the Pipe

• Let first address the case where we want to have
  objects flowing over the pipe
• Must have at least the following mechanisms for
• Objects to be written by the server
• Objects to be read by the client

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The new protocol Client
public class Client Socket socket new
Socket( "127.0.0.1", 9999 ) //
ObjectInputStream input new
ObjectInputStream(socket.getInputStream() )
// read using serialization NewProtocol
protocol (NewProtocol)(input.readObject() )
System.out.println(Protocol protocol)
socket.close()
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The new protocol Server
class ThreadedSocket extends Thread // here is
where all the real work is done. private Socket
socket ThreadedSocket( Socket socket )
this.socket socket //
ObjectOutputStream output new
ObjectOutputStream(socket.getOutputStream() )
output.writeObject( protocol )
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File example

• For example to write an object that can be read
  by the example in ObjectInputStream

FileOutputStream ostream new FileOutputStream(f
oo.bar") ObjectOutputStream p new
ObjectOutputStream(ostream) p.writeInt(12345) p.
writeObject("Today") p.writeObject(new
Date()) p.flush() ostream.close()
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The Needed Java Framework

• Only objects that support the java.io.Serializable
  interface can be written to streams.
• The class of each serializable object is encoded
  including the class name and signature of the
  class, the values of the object's fields and
  arrays, and the closure of any other objects
  referenced from the initial objects
• This relates to introspection/reflection which we
  will discuss shortly

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More about the Framework

• The default deserialization mechanism for objects
  restores the contents of each field to the value
  and type it had when it was written.
• Marshalling of Objects (Serialize)
• Un marshaling of Object (Serialize)

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Retrieving Class Objects

• You can retrieve a Class object in several ways
• Class c foo.getClass() // for some object
  named foo
• Bar b new Bar()
• Class c b.getClass()
• Class s c.getSuperclass()

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Getting the Class Name

• Every class in the Java programming language has
  a name. When you declare a class, the name
  immediately follows the class keyword
• At runtime, you can determine the name of a Class
  object by invoking the getName method. The String
  returned by getName is the fully-qualified name
  of the class.
• A good home study question Given an instance
  prints the names of the classes its inheritance
  hierarchy from least specific to most specific
  excluding Object

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An Example
import java.lang.reflect. import java.awt.
class SampleName public static
void main(String args) Button
b new Button() printName(b)
static void
printName(Object o) Class c
o.getClass() String s
c.getName() System.out.println(s
)
Need Reflection Package To Do this
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