Transcript URLs, InetAddresses, and URLConnections

Chapter 3
Internet Addressing
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Prepared By E.Musa Alyaman
Chapter 3 Outline
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Hosts
Internet addresses
Next Generation Internet
IPv4
Class A,B and C addresses
Domain Name System (DNS)
Creating InetAddresses
Java 1.4 Added Methods
Getter Methods
Address Types
Object Methods
Chapter 3 Highlights
Prepared By E.Musa Alyaman
Hosts
• Devices connected to the Internet are
called hosts
• Most hosts are computers, but hosts also
include routers, printers, fax machines,etc.
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Internet addresses
• Every host on the Internet is identified by
a unique, four-byte Internet Protocol (IP)
address.
• This is written in dotted quad format like
199.1.32.90 where each byte is an
unsigned integer between 0 and 255.
• There are about four billion unique IP
addresses, but they aren’t very efficiently
allocated
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Next Generation Internet
• The solution is IPv6 which uses 128 bit addresses
• Improves services such as multicasting and secure
communication
• Not yet widely deployed by ISPs
• Well written Java software should move to IPv6 without
modification/recompilation this is one benefit of
abstracted APIs
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IPv4
• Each 32 bit IP number consists of two
components:
– The network address
• The unique international address of the network
– The host address
• The unique address of a specific host in the net
• There are three classes of network
address denoted class ‘A’, ‘B’ and ‘C’
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Class A,B and C addresses
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Class A
0...
Class B
10...
Class C
110...
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Network Address Byte
Host Address Byte
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Domain Name System (DNS)
• Numeric addresses are mapped to names
like www.msn.com or mail.msn.com by
DNS.
• Each site runs domain name server
software that translates names to IP
addresses and vice versa
• DNS is a distributed system
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IP Addresses and Java
• Java has a class java.net.InetAddress
which abstracts network addresses
• Serves three main purposes:
– Encapsulates an address
– Performs name lookup (converting a host
name into an IP address)
– Performs reverse lookup (converting the
address into a host name)
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Creating InetAddresses
• There are no public InetAddress()
constructors. Arbitrary addresses may not
be created.
• All addresses that are created must be
checked with DNS
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Ways to create InetAddress objects
public static InetAddress getByName(String host)
throws UnknownHostException
public static InetAddress[ ] getAllByName(String
host) throws UnknownHostException
public static InetAddress getLocalHost() throws
UnknownHostException
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Java 1.4 Added Methods
• Java 1.4 adds two more factory methods that do not
check their addresses with the local DNS server. The
first creates an InetAddress object with an IP address
and no hostname. The second creates an InetAddress
object with an IP address and a hostname.
public static InetAddress getByAddress(byte[ ] address)
throws UnknownHostException
public static InetAddress getByAddress(String hostName,
byte[] address) throws UnknownHostException
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Getter Methods
They return the hostname as a string and the IP
address as both string and a byte array
• public String getHostName()
• public byte[ ] getAddress()
• public String getHostAddress()
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Address Types
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Public boolean isAnyLocalAddress()
Public boolean isLoopbackAddress()
Public boolean isLinkLocalAddress()
Public boolean isSiteLocalAddress()
Public boolean isMulticastAddress()
Public boolean isMCGloabl()
Public boolean isMCNodeLocal((
Public boolean isMCLinkLocal()
Public boolean isMCSiteLocal()
Public boolean isMCOrgLocal()
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Object Methods
• Public boolean equals (Object o)
• Public int hashCode ()
• Public String toString ()
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Inet4Address and Inet6Address
• Public final class Inet4Address extends
InetAddress
• Public final class Inet6Address extends
InetAddress
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Using
InetAddress
objects
import java.net.InetAddress;
import java.net.UnknownHostExcepion;
public static void main(String[] args)
{
try {
InetAddress inet1 =
InetAddress.getByName("asp.ee.uwa.edu.au");
System.out.println(
"HostAddress=" + inet1.getHostAddress());
InetAddress inet2 =
InetAddress.getByName("130.95.72.134");
System.out.println("HostName=" + inet2.getHostName());
if (inet1.equals(inet2))
System.out.println("Addresses are equal");
}
catch (UnknownHostException uhe) {
uhe.printStackTrace();
}
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}
Chapter Highlights
In this chapter, you have learned:
• About the Domain Name System (DNS)
and domain name suffixes (such as .com)
• About the structure of an IP address and
the various classes of IP addresses
• About the InetAddress class and its various
methods
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