JAVA. Sieťové programovanie

Transcription

1 JAVA Sieťové programovanie

2 Sieťové programovanie Sieťová knižnica jazyka JAVA bola vytvorená podľa súborovej knižnice Zapúzdrovanie pripojení do streamov Multithreading

3 Identifikácia počítača Každý počítač v Internete je jedinečne charakterizovaný IP adresou prideľovanou fixne (nemenne) alebo dynamicky prostredníctvom DHCP. Podobne má každý počítač meno zaznamenané v bázach dát DNS. Java umožňuje zistiť IP adresu počítača prostredníctvom volania metódy InetAddress.getByName(menoPočítača)

4 Identifikácia počítača import java.io.*; import java.net.*; public class WhoAmI { public static void main(string[] args) throws Exception { String meno = ""; InetAddress add; BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); System.out.print("Zadaj meno pocitaca: "); meno = in.readline(); catch (IOException e) { System.err.println("chyba s nacitanim"); add = InetAddress.getByName(meno); System.out.println(add);

5 Identifikácia počítača add = InetAddress.getByName(meno); System.out.println("meno/IP pocitaca: " + add); add = InetAddress.getByName(null); System.out.println("meno/IP localhost: " + add); add = InetAddress.getLocalHost(); System.out.println("meno/IP host pocitaca: " + add); System.out.println("meno host: " + add.gethostname()); System.out.println("IP host: " + add.gethostaddress());

6 Servery a klienti Server je počítač, ktorý čaká na prichadzajúce spojenie. Klient má za úlohu toto pripojenie vytvoriť. Rozdelenie Klient-Server po vytvorení spojenia stráca význam. Komunikácia prebieha ako keby to boli len súbory(.read,.write...)

7 Sokety Sokety (angl. sockets) sú softvérovou abstrakciou fyzických konektorov (zásuviek) komunikačného spojenia medzi počítačmi ServerSocket a Socket ServerSocket.accept(); InputStream a OutputStream

8 import java.io.*; import java.net.*; public class MojPrvyServer { private static ServerSocket ss; public static final int PORT = 8081; public static void main(string[] args) throws IOException { ss = new ServerSocket(PORT); System.out.println("Server beží: " + ss); Socket s = ss.accept(); BufferedReader in = new BufferedReader( new InputStreamReader( s.getinputstream())); PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( s.getoutputstream())), true); while(true) { String citam = in.readline(); if (citam.equals("end")) break; System.out.println ("Server prijíma: " + citam); System.out.println ("Server posiela: " + citam); out.println(citam); catch (IOException e) { System.err.println("IOException"); finally { System.out.println("Uzatváram sokety"); s.close(); finally { ss.close();

9 import java.io.*; import java.net.*; public class MojPrvyKlient { public static void main(string[] args) throws IOException { InetAddress ip = InetAddress.getByName(null); Socket s = new Socket(ip, MojPrvyServer.PORT); System.out.println("Štartuje klient: " + s); BufferedReader in = new BufferedReader( new InputStreamReader( s.getinputstream())); PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( s.getoutputstream())), true); for(int i = 0; i < 5; i ++) { out.println("posielam " + i); System.out.println ("Klient posiela: " + "posielam " + i); System.out.println ("Klient prijíma: " + in.readline()); out.println("end"); catch (IOException e) { System.out.println("IOException"); finally { s.close();

10 Viacvláknový server Predchadzajúci server dokázal obslúžiť iba jedného klienta. Aby sme mohli obsluhovať teoreticky neobmedzené množstvo klientov použijeme Vlákna.

11 import java.net.*; import java.io.*; public class MultivlaknovyServer { private static ServerSocket ss; public static final int PORT = 8081; public static void main(string[] args) throws IOException { ss = new ServerSocket(PORT); System.out.println("Server beží: " + ss); while(true) { Socket s = ss.accept(); new ObsluhaJednehoKlienta(s); finally { ss.close();

12 class ObsluhaJednehoKlienta extends Thread { private Socket socket; private BufferedReader in; private PrintWriter out; public ObsluhaJednehoKlienta(Socket s) { socket = s; in = new BufferedReader( new InputStreamReader( s.getinputstream())); out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( s.getoutputstream())), true); catch (IOException e) { System.err.println("IOException"); start(); public void run() { while(true) { String citam = in.readline(); if (citam.equals("end")) break; System.out.println("Server prijíma: " + citam); System.out.println("Server posiela: " + citam); out.println(citam); catch (IOException e) { System.err.println ("Chyba so zapisovaním alebo čítanim"); finally { socket.close(); catch(ioexception e) { System.err.println ("Nepodarilo sa uzavrieť soket");

13 Datagramy Nevýhody: Neisté doručenie paketov Neisté poradie doručenia Výhody: Rýchlosť prenosu Použitie: Pri prenose zvuku, prenos času

14 Datagramy Nerozlišujeme medzi serverom a klientom. Na oboch stranách sa vytvára DatagramSocket. Paket datagramu musí vedieť nielen kam ide ale aj odkiaľ ide.

15 Príklad triedy pre tvorbu DatagramPacketu a Stringu z Paketu import java.net.*; public class Dgram { public static DatagramPacket todatagram( String s, InetAddress destia, int destport) { byte[] buf = s.getbytes(); return new DatagramPacket(buf, buf.length, destia, destport); } public static String tostring(datagrampacket p){ return new String(p.getData(), 0, p.getlength()); } }

16 import java.net.*; import java.io.*; import java.util.*; public class ChatterServer { static final int INPORT = 1711; private byte[] buf = new byte[1000]; private DatagramPacket dp = new DatagramPacket(buf, buf.length); // Can listen & send on the same socket: private DatagramSocket socket; public ChatterServer() { socket = new DatagramSocket(INPORT); System.out.println("Server started"); while(true) { // Block until a datagram appears: socket.receive(dp); String rcvd = Dgram.toString(dp) + ", from address: " + dp.getaddress() + ", port: " + dp.getport(); System.out.println(rcvd); String echostring = "Echoed: " + rcvd; // Extract the address and port from the // received datagram to find out where to // send it back: DatagramPacket echo = Dgram.toDatagram(echoString, dp.getaddress(), dp.getport()); socket.send(echo); catch(socketexception e) { System.err.println("Can't open socket"); System.exit(1); catch(ioexception e) { System.err.println("Communication error"); e.printstacktrace(); public static void main(string[] args) { new ChatterServer();

17 import java.lang.thread; import java.net.*; import java.io.*; public class ChatterClient extends Thread { // Can listen & send on the same socket: private DatagramSocket s; private InetAddress hostaddress; private byte[] buf = new byte[1000]; private DatagramPacket dp = new DatagramPacket(buf, buf.length); private int id; public ChatterClient(int identifier) { id = identifier; // Auto-assign port number: s = new DatagramSocket(); hostaddress = InetAddress.getByName("localhost"); catch(unknownhostexception e) { System.err.println("Cannot find host"); System.exit(1); catch(socketexception e) { System.err.println("Can't open socket"); e.printstacktrace(); System.exit(1); System.out.println("ChatterClient starting");

18 public void run() { for(int i = 0; i < 25; i++) { String outmessage = "Client #" + id + ", message #" + i; // Make and send a datagram: s.send(dgram.todatagram(outmessage, hostaddress, ChatterServer.INPORT)); // Block until it echoes back: s.receive(dp); // Print out the echoed contents: String rcvd = "Client #" + id + ", rcvd from " + dp.getaddress() + ", " + dp.getport() + ": " + Dgram.toString(dp); System.out.println(rcvd); catch(ioexception e) { e.printstacktrace(); System.exit(1); public static void main(string[] args) { for(int i = 0; i < 10; i++) new ChatterClient(i).start();

19 KONIEC