Download Networking Java (2/3) - SPARCS

Networking Java (2/3)
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Java UDP basic
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TCP vs UDP : reliability vs speed
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Using UDP : NFS, DNS, TFTP
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Not a stream, but a packet.
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UDP Packet Size upperbound : 64Kbytes
8Kbytes is a good compromise.
includes IP header : 20 - 60 bytes, UDP header : 8 bytes
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Translating the data into a byte array.
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You shoud call receive() in a separate thread.
Class DatagramPacket
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Constructors
DatagramPacket(byte[], int)
DatagramPacket(byte[], int, InetAddress, int)
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Methods
getAddress()
getData()
getLength()
getPort()
setAddress(InetAddress)
setData(byte[])
setLength(int)
setPort(int)
Sending Packet
import java.net.*;
public class UDPSender {
public static void main( String[] args ) {
String s = "This is a test.";
byte[ ] data = new byte[ s.length( ) ];
data = s.getBytes( );
try {
InetAddress ia = InetAddress.getByName( "sunsite.unc.edu
" );
int port = 7;
DatagramPacket dp = new DatagramPacket( data, data.leng
th, ia,
port );
}
catch ( UnknownHostException e ) {
}
}
}
Receiveing Packet
import java.net.*;
public class UDPReceiver
{
public static void main( String[] args )
{
byte[ ] buffer = new byte[ 8096 ];
DatagramPacket dp = new DatagramPacket( buffer, buffer.lengthi
);
}
}
DatagramSocket
Constructor
DatagramSocket()
DatagramSocket(int)
DatagramSocket(int, InetAddress)
Methods
close()
getLocalAddress()
getLocalPort()
getSoTimeout()
receive(DatagramPacket)
send(DatagramPacket)
setSoTimeout(int)
DatagramSocket
import java.net.*;
public class lookForLocalUDPPorts {
public static void main( String[] args ) {
DatagramSocket theServer;
for ( int i = 1024; i <= 65535; i ++ ) {
try {
// the next line will fail and drop into the catch block if
// there is already a server ruuning on port i
theServer = new DatagramSocket( i );
theServer.close( );
}
catch ( SocketException e ) {
System.out.println( "There is a server on port"+ i + "." );
}
// end try
}
// end for
}
}
alpha:~/Java/Seminar/Networking> time java lookForLocalUDPPorts
There is a server on port2049.
19.720u 14.130s 0:36.50 92.7% 0+0k 0+0io 1493pf+0w
UDPDiscardClient 1/2
import java.net.*;
import java.io.*;
public class UDPDiscardClient {
public final static int
port = 9999;
public static void main( String[] args ) {
String hostname;
if ( args.length > 0 ) {
hostname = args[ 0 ];
}
else {
hostname = "localhost";
}
try {
String theLine;
DatagramPacket theOutput;
InetAddress
);
server = InetAddress.getByName( hostname
UDPDiscardClient 2/2
DataInputStream userInput = new DataInputStream( System.
in );
DatagramSocket theSocket = new DatagramSocket( );
while ( true ) {
theLine = userInput.readLine( );
if ( theLine.equals( "." ) ) break;
byte[ ] data = new byte[ theLine.length( ) ];
theLine.getBytes( 0, theLine.length( ), data, 0
);
theOutput = new DatagramPacket( data, data.lengt
h, server,
port );
theSocket.send( theOutput );
}
// end while
}
// end try
catch ( UnknownHostException se ) {
System.err.println( se );
}
catch ( IOException e ) {
System.err.println( e );
}
}
}
// main
UDPDiscardServer 1/2
import java.net.*;
import java.io.*;
public class UDPDiscardServer {
public final static int discardPort = 9999;
static byte[ ] buffer = new byte[ 65507 ];
public static void main( String[ ] args ) {
int
port;
try {
port = Integer.parseInt( args[ 0 ] );
}
catch ( Exception e ) {
port = discardPort;
}
UDPDiscardServer 2/2
try {
DatagramSocket ds = new DatagramSocket( port );
DatagramPacket dp = new DatagramPacket( buffer, buffer.
length );
while ( true ) {
try {
ds.receive( dp );
String s = new String( dp.getData( ), 0
, dp.getLength( ) );
System.out.println( dp.getAddress( ) + "
at port " +
dp.getPort( ) + " says " + s );
}
catch ( IOException e ) {
System.err.println( e );
}
}
}
catch ( SocketException se ) {
System.err.println( se );
}
}
}
Protocol Handler
dgtprotocol:*&$sparcs.kaist.ac.kr/image/content.dgt
Extensible browser.
( vs Netscape Pulg-In ? )
Sun divided the problem into two parts: hanlding protocols, handling contents.
The constructor, URL( ), strips the protocol field and uses it to call the
URLStreamHandlerFactory. The factory's job is to take the protocol, locate an
appropriate stream handler, which is stored as a field whithin the URL object.
at most one URLStreamHandlerFactory.
URLStreamHandler finish parsing the URL string and to create a subclass of
URLConnection that knows how to deal with servers for this protocol.
URLStreamHandlers and URLConnections are always paired.
a Java browser can be a relatively lightweight skeleton that loads new
handlers as needed.
Class downloading via network!!!
URL.setURLStreamHandlerFactory( new myURLStreamHandlerFactory( ) );
once in the lifetime of an application.
Netscape Navigator and Internet Explorer don't load protocol handlers
dynamically; you're limited to the protocols they provide.
Sun.net.www.protocol
alpha:~/Java/classes/sun/net/www/protocol> ls -al
total 12
drwxr-xr-x 12 dgtgrade 200
1024 Jul 2 17:28 ./
drwxr-xr-x 6 dgtgrade 200
1024 Jul 2 17:28 ../
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 appletresource/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 doc/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 file/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 ftp/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 gopher/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 http/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 mailto/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 netdoc/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 systemresource/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 verbatim/
Implement the Protocol
extends URLConnection
public void connect() throws
IOException;
public String getContentType( );
public synchronized InputStream
tion;
getInputStream( ) throws IOExcep
Handler
import java.net.*;
import java.io.*;
import java.util.*;
public class Handler extends java.net.URLStreamHandler {
protected
URLConnection openConnection( URL u ) throws
IOExcept
ion {
return new mailtoURLConnection( );
}
protected
void parseURL( URL u, String spec, int start, int lim
it ){
StringTokenizer st = new StringTokenizer( spec.substring( start
),
":@", flase );
String protocol = st.nextToken( );
String file = st.nextToken( );
String host = st.nextToken( );
String ref = st.nextToken( );
int port = 25;
setURL( u, protocol, host, port, file, ref );
}
protected
String toExternalForm( URL u ) {
return "mailto:" + u.getFile() + "@" + u.getHost( );;
}
}
chargen://hostname:port
1/2
package sun.net.www.protocol.chargen;
import java.net.*;
import java.io.*;
public class chargenURLConnection extends URLConnection {
Socket theConnection = null;
public final static int defaultPort = 19;
public chargenURLConnection( URL u ) {
super( u );
}
public synchronized InputStream
tion {
getInputStream( ) throws IOExcep
if ( !connected ) {
connect( );
}
return theConnection.getInputStream( );
}
public String getContenetType( ){
return "text/plain";
}
chargen://hostname:port
2/2
public synchronized void connect( ) throws
int
IOException {
port;
if ( !connected ) {
port = url.getPort( );
if ( port < 0 ) {
port = defaultPort;
}
theConnection = new Socket( url.getHost( ), port );
connected = true;
}
}
}
Factory
public URLStreamHandler
createURLStreamHandler( String protocol ) {
if ( protocol.equalsIgnoreCase( "chargen" ) ) {
return new chargenURLStreamHandler( );
}
else {
return null;
}
}
HotJava Usage :
set CLASSPATH
Update the Properties File
java.protocol.handler.pkgs=ORG.netspace.dwb.protocol|COM.company.pro
toco
l
Content Handler
alpha:~/Java/classes/sun/net/www/content> ls -al
total 4
drwxr-xr-x 4 dgtgrade 200
1024 Jul 2 17:28 ./
drwxr-xr-x 6 dgtgrade 200
1024 Jul 2 17:28 ../
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 image/
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 text/
alpha:~/Java/classes/sun/net/www/content> ls -al image
total 6
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 ./
drwxr-xr-x 4 dgtgrade 200
1024 Jul 2 17:28 ../
-rw-r--r-- 1 dgtgrade 200
475 May 12 12:10 gif.class
-rw-r--r-- 1 dgtgrade 200
477 May 12 12:10 jpeg.class
-rw-r--r-- 1 dgtgrade 200
487 May 12 12:10 x_xbitmap.class
-rw-r--r-- 1 dgtgrade 200
487 May 12 12:10 x_xpixmap.class
alpha:~/Java/classes/sun/net/www/content> ls -al text
total 5
drwxr-xr-x 2 dgtgrade 200
1024 Jul 2 17:28 ./
drwxr-xr-x 4 dgtgrade 200
1024 Jul 2 17:28 ../
-rw-r--r-- 1 dgtgrade 200
273 May 12 12:10 Generic.class
-rw-r--r-- 1 dgtgrade 200
320 May 12 12:10
PlainTextInputStream.class
-rw-r--r-- 1 dgtgrade 200
848 May 12 12:10 plain.class
Content Handler
URL's getContent() return an object representing the contents of the
resource.
URLConnection.getContent( ) calls URLConnection.getContentHandler( )
getContentHandler() checks cache.
MIME type, MIME subtype
when ContentHandlerFactory is null, Java looks content handler classes for
sun.n
et.www.content.type.subtype
abstract class ContentHandler
Constructor
ContentHandler()
Methods
getContent(URLConnection)
interface ContentHandlerFactory
Methods
createContentHandler(String)