Post on 05-Jan-2016
description
Networking Java (2/3)
dgtgrade@sparcs.kaist.ac.kr
Java UDP basic
• TCP vs UDP : reliability vs speed
• Using UDP : NFS, DNS, TFTP
• Not a stream, but a packet.
• UDP Packet Size upperbound : 64Kbytes
• 8Kbytes is a good compromise.
• includes IP header : 20 - 60 bytes, UDP header : 8 bytes
• Translating the data into a byte array.
• You shoud call receive() in a separate thread.
Class DatagramPacket
• Constructors
• DatagramPacket(byte[], int)
• DatagramPacket(byte[], int, InetAddress, int)
• 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 Handlerdgtprotocol:*&$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.protocolalpha:~/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 getInputStream( ) throws IOExcep
tion;
Handlerimport 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 getInputStream( ) throws IOExcep
tion {
if ( !connected ) {
connect( );
}
return theConnection.getInputStream( );
}
public String getContenetType( ){
return "text/plain";
}
chargen://hostname:port2/2
public synchronized void connect( ) throws IOException {
int 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.protoco
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)