Download session4 - Advanced Java 2

Advanced Java
Session 4
New York University
School of Continuing and Professional Studies
Objectives
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Networking Basics
– Topologies, Layers, Communications
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Command line tools
Network programming basics
– Sockets, TCP/IP stack
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Java Network Programming
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Creating sockets
Implementing servers
URLs and URLConnections
Protocol Handlers
Content Handlers
Advanced concepts in Sockets
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Secure Sockets – Client and Server
Channels (Non-Blocking I/O)
UDP_ Datagrams and Sockets
Multicast Sockets
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Bus
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Star
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Sample Network
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ISO stack and TCP/IP stack
Application
Presentation
Session
Transport
Network
Application
Transport
(TCP & UDP)
Internet
(IP)
Data Link
Physical
ISO Reference Model
Network Interface
TCP Reference Model
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Network Communications
Machine A
Machine B
Application
Application
Packets
Transport
Transport
Internet
Internet
Network Interface
Network Interface
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TCP/IP stack
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IP
• Java supports only IP based networks
• IP (Internet Protocol) has a number of
advantages over competing protocols such
as AppleTalk and IPX etc.
• Robust (multiple routes between any 2
points)
• Cross platform
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TCP
• Layered on top of IP
• Guaranteed delivery of packets “in the order
in which they were sent”
• Carries a fair amount of overhead
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UDP
• Layered on top of IP
• Unreliable
• No guarantee that packets will arrive at the
destination or even arrive at all
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IP Addresses
• Every Computer is identified by a 4 byte
(IPV4) number (e.g. 66.95.177.137 )
• Slow transition to IPV6 is underway which
uses a 16 byte number for addresses (since
JDK 1.4)
• NAT and IP Masquerading allow reuse of
same IP addresses in networks separated by
a router/firewall
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Multicasting
• Middle ground between “unicasting” (pointto-point) and “broadcasting” (to-everybody)
• Address range between 224.0.0.0 (reserved)
to 239.255.255.255
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Domain Name System
• Top Level Domains – com, net, org, … are
served by “ROOT” dns servers run by
InterNic
• All domains must be registered with
Internic
• Delegate model is used to allow
organizations to control their own set of
names
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Sockets and Ports
Source ip
Source port
Destination ip
Destination port
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TCP/IP Session
• Source machine creates
a socket and attempts to
connect to a destination
machine by giving its
“ip” and “port”
numbers
• Source machine
responds with
ConnectionAccepted
• If the destination
machine is listening on
that port “and” accepts
this connection it
responds with “request
accepted”
Data can now be transferred until an EOF is
seen or a Network Error occurs
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Some Useful Commands
• telnet <host> <port> - connects to given
host and port
• netstat – shows status of TCP/IP activity
• nslookup – used to look up IP Addresses of
host names
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Examples
• SocketTest.java
– Simple socket client
• EchoServer.java
– Simple Socket Server
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Examples
• ThreadedEchoServer.java
– Multithreaded Socket Server
– Can service multiple clients
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The java.net package
• Contains classes and interfaces that can be used to
write network programs in Java
• InetAddress, Inet4Address and Inet6Address
• NetworkInterface class
• SocketImpl class
• SocketAddress (abstract) and InetSocketAddress
(implements Serializable)
• Socket, ServerSocket, DatagramSocket
• URL, URLConnection, HttpURLConnection
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The javax.net and javax.net.ssl
packages
• Contains classes and interfaces that can be
used to create SSL Sockets
• SocketFactory, ServerSocketFactory in
javax.net
• SSLSocketFactory,
SSLServerSocketFactory in javax.net.ssl
• SSLSocket, SSLServerSocket
• HttpsURLConnection
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java.nio and java.nio.channels
• Data Buffers for storing and manipulating
raw data before and after I/O
• Channels for reading and writing from
entities that are capable of performing I/O
such as files, devices and sockets
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More Examples
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HostLookup.java
InterfaceLister.java
PortScanner.java (uses socket factory)
ChargenServer.java and ChargenClient.java
(demonstrate SocketChannel and non-blocking
operations on sockets)
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UDP Examples
• UDPServer.java and UDPEchoServer.java
• UDPClient.java
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Multicast Examples
• MulticastSniffer.java
• MulticastSender.java
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URLConnection examples
• AllHeaders.java
• HttpGetter.java
• FormPoster.java
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Java Mail API
• SMTPClient.java
• SMTPApplet.java
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Network Security and Applets
• Can’t connect to servers other than the one it
was downloaded from.
• Can’t access local hard disk
• Signed applets may be permitted to override
the security – provided that the user permits it.
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Thank you
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