Download An Introduction to Control Structures

Networking Programming
Chapter 11
Java Programming: Advanced Topics
1
Objectives
• Perform network I/O using the core
classes in the package java.net
• Write programs that establish connections
to URLs and perform stream I/O between
URLs
• Read and write data to local and remote
sites using TCP/IP sockets and datagram
sockets
Java Programming: Advanced Topics
2
Objectives (Cont.)
• Use Remote Method Invocation
(RMI) to develop classes of
objects that are accessible from
a server
• Learn the steps involved in compiling
and deploying an application that
uses RMI
Java Programming: Advanced Topics
3
Objectives (Cont.)
• Be introduced to the Java Naming and
Directory Interface (JNDI)
• Discover the relationship between
CORBA, RMI-IIOP, and the Java Interface
Definition Language (IDL)
Java Programming: Advanced Topics
4
Introduction
• The Java platform includes a package
java.net to perform input and output (I/O)
operations over the network
• Core classes of the java.net package
support URLs, TCP/IP sockets, or datagram
sockets
Java Programming: Advanced Topics
5
Working with URLs
• URLs begin with a protocol specification
followed by a colon and two forward slashes
(://) and the host name, along with optional file
and port information
• To exchange information with a URL, you
must create a URLConnection by calling the
method openConnection for a URL
Java Programming: Advanced Topics
6
The Use of the URL and
URLConnection Objects
Java Programming: Advanced Topics
7
The Use of the URL and
URLConnection Objects (Cont.)
Java Programming: Advanced Topics
8
Working with URLs (Cont.)
• Uniform Resource Identifier (URI) technology
has become commonly used in technical
specifications in place of the term URL
• The class java.net.URI contains a method,
toURL, which can be used to construct a URL
object from a URI object
Java Programming: Advanced Topics
9
Working with Sockets
• Socket: an abstraction of the end points
of connections between processes or
applications
• The Java platform supports two types of
sockets:
– TCP/IP
– datagram
Java Programming: Advanced Topics
10
TCP/IP Sockets
• A TCP/IP socket is connection-oriented
• Create a Socket object, ask the socket for its
input stream and output stream
• To perform stream I/O to and from a TCP/IP
socket, use the methods Socket.getInputStream
and Socket.getOutputStream
• Use the ServerSocket class to create the server
side of a TCP/IP socket
Java Programming: Advanced Topics
11
Datagram Sockets
• Datagram sockets send packets that contains
information that identifies the network
destination in addition to the content of your
message
• The class DatagramPacket represents these
packets
• The User Datagram Protocol (UDP) used by
these sockets makes no attempt to recover from
lost or damaged packets
Java Programming: Advanced Topics
12
An Example Datagram Socket
Server Program
Java Programming: Advanced Topics
13
An Example Datagram Socket
Server Program (Cont.)
Java Programming: Advanced Topics
14
An Example Datagram Socket
Server Program (Cont.)
Java Programming: Advanced Topics
15
An Example Datagram Socket
Client Program
Java Programming: Advanced Topics
16
An Example Datagram Socket
Client Program (Cont.)
Java Programming: Advanced Topics
17
Remote Method Invocation
• Remote Invocation Method (RMI) is a
technology that allows programmers to call
directly the methods of Java objects that reside
on other systems
• Client programs use Object Request Brokers
(ORBs) to obtain references to these remote
objects
• Marshaling: the technique used to forward the
parameters to the remote object
Java Programming: Advanced Topics
18
Remote Method Invocation
• Stub classes act as local surrogates for remote
objects to provide access to the remote objects
• Skeleton classes marshal and unmarshal
parameters and return values between the stub
and the remote object
• On the remote system, a skeleton object
receives this byte stream and uses a technique
called unmarshaling to deserialize the contents
of the parameter list
Java Programming: Advanced Topics
19
Flow of a Remote Method Call
Java Programming: Advanced Topics
20
Developing a Remote Class of
Objects
• The Remote interface is a marker interface
• To make an interface available remotely via
RMI, it should extend the java.rmi.Remote
• All methods in the interface must indicate that
they might throw a java.rmi.RemoteException
Java Programming: Advanced Topics
21
Remote Interface
Java Programming: Advanced Topics
22
Developing an RMI Server Class
Java Programming: Advanced Topics
23
Developing an RMI Server Class
(Cont.)
Java Programming: Advanced Topics
24
Developing an RMI Client Class
Java Programming: Advanced Topics
25
Developing an RMI Client Class
(Cont.)
Java Programming: Advanced Topics
26
Running the Server and
Client Programs
• Compile server and client files using the javac
compiler
• Create the stub and skeleton classes by using
the rmic command
• Start the RMI registry program by typing:
rmiregistry
• Start the server program and supply the
codebase for the stub and skeleton files
• Start the client program
Java Programming: Advanced Topics
27
JNDI
• Sun developed the Java Naming and
Directory Interface (JNDI)
• JNDI is not itself a naming or directory
service, but is a unified interface to
multiple naming and directory services
that already exist for enterprise
development
Java Programming: Advanced Topics
28
JNDI Packages
Java Programming: Advanced Topics
29
JNDI Packages (Cont.)
Java Programming: Advanced Topics
30
Corba, RMI-IIOP, and IDL
• Common Object Request Broker Architecture
(CORBA) is a generic architecture for defining
and using remote objects
• A consortium of companies, known as the Object
Management Group (OMG), developed the
CORBA standard
• CORBA ORBs use Internet Inter-ORB Protocol
(IIOP)
Java Programming: Advanced Topics
31
Corba, RMI-IIOP, and IDL (Cont.)
• The interfaces of CORBA objects are
defined using a language called Interface
Definition Language (IDL)
• Java platform SDK provides a tool called idlj
that generates the Java bindings for the
specified IDL file
Java Programming: Advanced Topics
32
Summary
• The java.net package supports network
programming
• The core classes of the java.net package
support URLs, TCP/IP sockets, or
datagram sockets
• To exchange information with a URL, you
must create a URLConnection object
• TCP/IP sockets are connection-oriented,
and datagram sockets use packets
Java Programming: Advanced Topics
33
Summary (Cont.)
• Remote Invocation Method (RMI) is a technology
that allows programmers to call directly the
methods of Java objects that reside on other
systems
• The Java Naming and Directory Interface (JNDI)
is a unified interface to multiple naming and
directory services that already exist for enterprise
development
• Common Object Request Broker Architecture
(CORBA) is a more generic architecture for
defining and using remote objects
Java Programming: Advanced Topics
34