Java Network Program

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Java Network Program
Network Basic java.net Package Socket
Programming RMI Programming
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Network Basic

• Stream Socket
• Connection Service
• Use Transmission Control Protocol (TCP)
• Need Connection Time Before Communication
• Datagram Socket
• Connectionless Service
• Use User Datagram Protocol (UDP)
• Transmit Each Packet Independently
• Dont Need Connection Setup
• Need Complement of Reliability
• Server and Client

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Network Basic

• Transmission Control Protocol(TCP)
• Set up the Connection first, then Send Data
• After Exchanging Data, Need the Procedure for
  Releasing Connection
• Similar to Telephone Communication
• High Reliability
• High overload to release the connection -gt Not
  efficient for small data
• User Datagram Protocol(UDP)
• Without Connection, Split data into Packet with
  fixed length, Attach address, then transmit
  them.
• Similar to Mail
• Low Reliability
• Port
• Data Address IP Address(Computer) Port Number

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Java Network Package
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Java.Net Package Class Description
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URL Class

• Class URL represents a Uniform Resource Locator,
  a pointer to a "resource" on the World Wide Web.
• A resource can be something as simple as a file
  or a directory, or it can be a reference to a
  more complicated object, such as a query to a
  database or to a search engine
• Name of resource consists of host name, file
  name, port number, and reference
• URL Objects
• URL u-aizu new URL("http//www.u-aizu.ac.jp/")
• URL location new URL(u-aizu, location/welcome.h
  tml")
• URL software new URL(u-aizu, welcome/software.h
  tml")
• URL hardware new URL(u-aizu, welcome/hardware.h
  tml")

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Methods of URL Class

• Methods of URL class
• getProtocol() Return the protocol of URL Address
• getHost() Return the host name of URL Address
• getPort() Return the port number of URL Address
• getFile() Return the file name of URL Address
• getRef() Return the reference of URL Address
• InputStream openStream() Return the stream
  connected to URL
• URLConnection openConnection() Return the URL
  Connection object connected to this URL

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URL Class

• Communication Using URL Class
• Can read contents like input stream to use
  openStream method
• (Ex TestURLRead.java)
• Upload HTML document using URL Class
• Use showDocument() method of AppletContext
• (Ex TestShowDocument.java)
• URLConnection Class
• Have many methods to communicate with URL on
  network
• Open Connection() method
• (Ex TestURLConnectionRead.java)

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Socket Class

• Give Low Level Communication Mechanism
• Client-Server Application Program
• Database Query/Reply
• What is Socket?
• Structure for TCP
• End point for connecting entities
• Using the Port
• Exists between application program and port
• Ex) FTP server and Client

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Socket and ServerSocket Class

• Socket and ServerSocket
• To implement Connecting Client Side and Server
  Side
• Platform Independently
• Socket Class
• Methods
• InputStream getInputStream() Return Input Stream
  Socket Uses
• OutputStream getOutputStream() Return Output
  Stream Which Socket Uses
• Inetaddress getInetAddress() Return Internet
  Address Which Socket is Connected
• public int getLocalPort() Return the Port Number
  Socket is Connected
• public int getPort() Return the Remote Host
  Port Number
• public InetAddress getLocalAddress() Return the
  Internet Address which Socket is Connected

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Socket and ServerSocket Class

• ServerSocket Class
• Constructor
• public ServerSocket(int port) throws IOException
• public ServerSocket(int port, int queue) throws
  IOException
• public ServerSocket(int port, int queue,
  InetAddress addr) throws IOException
• Methods
• public Socket accept() Accept the Connection
  Request
• public void close() Close the ServerSocket
• public Inetaddress getInetAddress() Return the
  Internet Address which Socket is connected
• public int getSoTimeout()
• public void setSoTimeout() Time out to
  Socket(millisecond)
• (Ex) Server.java and Client.java

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Remote Method Invocation

• Composition of RMI Applications Distributed
  Objects
• two separate programs a server and a client.
• A typical server application creates some remote
  objects, makes references to them accessible, and
  waits for clients to invoke methods on these
  remote objects.
• A typical client application gets a remote
  reference to one or more remote objects in the
  server and then invokes methods on them.
• RMI provides the mechanism by which the server
  and the client communicate and pass information
  back and forth. Such an application is sometimes
  referred to as a distributed object application.

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Remote Method Invocation

• Distributed object applications need
• Locate remote objects Applications can use one
  of two mechanisms to obtain references to remote
  objects. An application can register its remote
  objects with RMI's simple naming facility, the
  rmiregistry, or the application can pass and
  return remote object references as part of its
  normal operation.
• Communication with remote objects Details of
  communication between remote objects are handled
  by RMI to the programmer, remote communication
  looks like a standard Java method invocation.
• Loadable class bytecodes for objects that are
  passed around Because RMI allows a caller to
  pass objects to remote objects, RMI provides the
  necessary mechanisms for loading an object's
  code, as well as for transmitting its data.

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Remote Method Invocation

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RMI Programming

• Writing an RMI Server
• The server is comprised of an interface and a
  class. The interface provides the definition for
  the methods that can be called from the client.
  Essentially the interface defines the client's
  view of the remote object. The class provides the
  implementation.
• Designing a Remote Interface
• Design a Remote interface, which provides the
  connection between the client and the server.
• Implementing a Remote Interface
• Class that implements the interface, thereby
  implementing a remote object. This class also
  provides the rest of the code that makes up the
  server program a main method that creates an
  instance of the remote object, registers it with
  the naming facility, and sets up a security
  manager.

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RMI Programming

• Creating a Client Program

• Ex) ComputePi.java, ComputeEngine.java,
• Pi.java

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RMI Programming

• Running Example Program

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Program Structure(Example)
Package client
Package compute
Package engine
ComputePi.java
Compute.java
ComputeEngine.java
Pi.java
Task.java
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RMI Programming

• Running Example Program
• A Note about Security
• grant
• permission java.net.SocketPermission
  "1024-65535", "connect,accept" permission
  java.net.SocketPermission "80", "connect"
• Start the Server
• unsetenv CLASSPATH
• rmiregistry

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RMI Programming

• Running Example Program
• Start the Server
• unsetenv CLASSPATH
• rmiregistry
• setenv CLASSPATH /home/ann/src/home/ann/public
  _html/classes/compute.jar
• java -Djava.rmi.server.codebasehttp//zaphod/ann
  /classes/
• -Djava.rmi.server.hostnamezaphod.east.sun
  .com
• -Djava.security.policyjava.policy
  engine.ComputeEngine

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RMI Programming

• Start the Client
• setenv CLASSPATH /home/jones/src/home/jones/pub
  lic_html/classes/compute.jar
• java Djava.rmi.server.codebasehttp//ford/jon
  es/classes/
• -Djava.security.policyjava.policy
  client.ComputePi
• zaphod.east.sun.com 20
• Compile and Run Example
• Refer examples/RMI/compileANDrun.txt