Advanced Programming Topics - II

1
Advanced Programming Topics - II

• Objectives
• Background
• Remoting
• Types of remoting
• Marshalling
• Farmatters
• Channels

2
Background

• Networking computers share resources and data
  amongst them in a cohesive manner
• Today various computer applications use
  distributed computing in one form or the other
• File servers, web application servers, print
  servers
• Nowadays , the processing power of computers is
  sufficiently advanced and their use became
  widespread
• So, why not harness the power of many personal
  computers in tandem and using them to process
  data?

3
Background

• To harness the computational computer power of
  several computers, some distributed technologies
  came into light
• Common Object Request Broker Architecture CORBA
  by Object Management Group (OMG)
• Remote Method Invocation (RMI) by Sun
  Microsystems
• Distributed Component Object Mode (DCOM) by
  Microsoft
• Web services invented by IBM Global Services

4
Background
CORBA RMI DCOM
Object Implementation Diverse languages can be used as long as the IDL can be mapped to that language. Only Java language can be applied, because the Java Object Serialization usage. Specification is at the binary level. Diverse languages like C, Java, Delphi, and even COBOL can be used.
Client/Server Interface The client stub is called a stub, and the server side is skeleton. The client stub is called a stub, and the server side is skeleton. The client stub is called a proxy, and the server side is called stub.
Object Location and Activation The ORB is used to locate an object, and Object Adapter is used for activation. The object location and activation are on Java Virtual Machine (JVM) Use the Service Control Manager (SCM) to locate and activate an object.
On-demand Activation A client can bind to a naming or a trader service to activate a server object by obtaining a server reference. A client can do a lookup() on the remote server objects URL name to obtain the object reference. A client can do a CoCreateInstance() to activate a server object.
5
DCOM versus Web Services

• Both DCOM and Web Services are used to achieve
  distributed application development
• In DCOM
• the object will be created both on the client and
  server side
• The client side object is called as Proxy and the
  server side object is called as Stub
• Once these two are created the proxy and stub
  interact with each other in sending and receiving
  the data remotely

6
DCOM versus Web Services

• In Web Services
• the object will be created only on the client
  side
• When a method is invoked from the client the
  proxy creates a request SOAP message and opens
  the http connection
• Then the request SOAP message is sent to the
  server through the http connection
• The Server then receives the request and converts
  it into the back end object and processes it
• The server then creates a response message and
  sends the response back to the client using the
  http connection
• The proxy receives it and converts into the
  required object and sends it to the client for
  further usage

7
Remoting

• When developing a distributed application, the
  underlying framework should provide transparent
  programming model to the application developer
• Proxies play major role in this area
• The proxy object acts as a 'dummy' of the remote
  object and forward all the method calls to the
  remote object instance
• These proxy objects are created at client end
• The client is unaware of the actual location of
  the remote object
• The client simply calls the methods on the proxy
  object which are then forwarded to the actual
  object

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Types of Remoting MBV

• There are two ways an object in one application
  domain can be made available to another
  application domain
• The first option involves serializing the object,
  transport it to the other domain using streams
• The object is then de-serialized and used at the
  other side
• This version is called Marshall by value (MBV)
• MBV should be considered only if the object does
  not depend on any data in its original domain

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Types of Remoting (MBR)

• The second type of remoting is called Marshall by
  reference (MBR)
• In this case, the client communicates with the
  remotable object through a proxy, but the object
  remains in its application domain
• To the client, the proxy appears as if it is the
  actual object
• However, for each call made to the proxy, the
  proxy passes the call to the remote object using
  a communication channel, obtain a result from the
  remote object and pass same to the client

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Remoting Formatters

• The communication between the client and remote
  object involves method parameters and return
  values
• This data must be serialized before it is sent
  across the network
• The serialization process creates a persistent
  copy of the data as a sequence of bytes
• The process of converting these bytes back into
  the original data structure is called
  de-serialization
• Formatters perform the serialization and
  de-serialization processes

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Remoting Formatters

• Formatters are available in following
  namespacesSystem.Runtime.Serialization.Formatte
  rs.Binary System.Runtime.Serialization.Formatters.
  SOAPAs the names suggest Binary formatter deals
  with data in binary format while SOAP formatter
  deals with data in XML format

12
Remoting Channels

• To communicate with remote object we need a path
  through which the data transfer can take place
• This path is called as Channel. There are two
  types of channels
• TCP channels these channels use TCP for
  communication TCP channels typically carry data
  in binary form i.e. they use Binary formatters
• HTTP Channels These channels use HTTP for
  communication. They typically carry SOAP messages
  i.e. they use SOAP formatters

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Remoting Channels

• TCP channels with Binary formatters are suitable
  where speed and performance is important
• HTTP Channels with SOAP formatters are suitable
  for platform independent or over the web
  communication
• The channels are available in following
  namespacesSystem.Runtime.Remoting.Channels.TCP
  System.Runtime.Remoting.Channels.HTTP

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How Does Remoting Work?

• When the client application communicates with the
  remote object following steps are involved
• At Server Side
• A Channel is established at a specific port which
  will listen to all client requests
• Remote object registers itself with remoting
  framework and declares its presence over the
  network   
• At Client Site
• Client establishes a channel at a specific port
  to talk with remote object
• Client creates an instance of remote object by
  calling Getobject or CreateInstance or new method
• Client gets the proxy for the remote object
• Client calls remote object methods on the proxy

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Remoting Server

• This is an application that a client connects to
  in order to gain access to the method of the
  remotable class
• Such an application must do three things as
  follows
• Create a communication channel This can be done
  with either the TcpChannel class of
  System.Runtime.Remoting.Channels.Tcp namespace,
  or using the HttpChannel class of
  System.Runtime.Remoting.Channels.Http namespace
• Register the communication channel created with
  the remoting channel services

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Remoting Server

• This is done by passing the channel to the static
  method, RegisterChannel, of the ChannelServices
  class, which is in the System.Runtime.Remoting.Cha
  nnels namespace
• Register the remotable class with the remoting
  server
• This is done by using the static method,
  RegisterWellKnownServiceType of the
  RemotingConfiguration class, of the
  System.Runtime.Remoting namespace
• This method takes three arguments
• The type of the remotable class
• A URI identifier for the class, and
• Object creation mode

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Remoting Server

• Possible modes are SingleCall and Singleton,
  both of which are fields of the
  WellKnownObjectMode class
• SingleCall means a separate instance of the
  remotable class will be created for each call to
  the remotable class
• Singleton mode means, a single instance will be
  used for different calls for all clients
• Singleton is useful if you wish to retain the
  state across different calls

18
Remoting Client

• This is the application that is used to access
  the methods of the remotable class through the
  remoting server
• Here again, there are three things that the
  client class must do to communicate with the
  remotable class
• Create a channel. This must be of the same type
  as that of the remoting server
• Register the communication channel created with
  the remoting channel services
• Creating an instance of the proxy class. The
  proxy class is like an alias to the remotable
  class, so all calls to the remotable class are
  made through the proxy class
• Here we have two options
• We use the RegisterWellKnownClientType of the
  RemotingConfiguration class. This takes the type
  of the remote class and its URI as arguments
• Alternatively, we can use the getObject method of
  the Activator class, which is in the System
  namespace

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Example RemotingServer.cs
using Systemusing System.IOusing
System.Runtime.Remotingusing System.Runtime.Remo
ting.Channels.HTTPnamespace RemotingServer
public class MyServer MarshalByRefObject
public MyServer() public string
GetString(string text) Console.WriteLine(text)
return "Hello " text public class
StartServer public static void Main(string s)
HTTPChannel channel new HTTPChannel(8000)Cha
nnelServices.RegisterChannel(channel)RemotingSer
vices.RegisterWellKnownType("remotingserver","Rem
otingServer.MyServer","ServerClassURI",WellKnownO
bjectMode.Singleton)Console.WriteLine("Press
enter to stop server...")Console.ReadLine()

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Example RemotingClient.cs
using Systemusing System.Runtime.Remotingusing
System.Runtime.Remoting.Channels.HTTPusing
RemotingServerpublic class RemotingClientpub
lic static void Main(string s)HTTPChannel
channel new HTTPChannel(8001)ChannelServices.R
egisterChannel(channel)MyServer server
(MyServer)Activator.GetObject(typeof(MyServer),
"http//localhost8000/ServerClassURI")Console.W
riteLine(server.GetString("Bipin"))