1	Modulo IIb Java Networking Programming Prof. Ismael H F Santos
2	Ementa Modulo IIb – Networking em JAVA Networking
3	Bibliografia Linguagem de Programação JAVA Ismael H. F. Santos, Apostila UniverCidade, 2002 The Java Tutorial: A practical guide for programmers Tutorial on-line: http://java.sun.com/docs/books/tutorial Java in a Nutshell David Flanagan, O´Reilly & Associates Just Java 2 Mark C. Chan, Steven W. Griffith e Anthony F. Iasi, Makron Books. Java 1.2 Laura Lemay & Rogers Cadenhead, Editora Campos
4	Livros Core Java 2, Cay S. Horstmann, Gary Cornell Volume 1 (Fundamentos) Volume 2 (Características Avançadas) Java: Como Programar, Deitel & Deitel Thinking in Patterns with JAVA, Bruce Eckel Gratuito. http://www.mindview.net/Books/TIJ/
5	POO-Java
6	Network Summary Internet Designed with multiple layers of abstraction Underlying medium is unreliable, packet oriented Provides two views Reliable, connection oriented (TCP) Unreliable, packet oriented (UDP) Java Object-oriented classes & API Sockets, URLs Extensive networking support
7	Introduction Internet and WWW have emerged as global ubiquitous media for communication and changing the way we conduct science, engineering, and commerce. They also changing the way we learn, live, enjoy, communicate, interact, engage, etc. It appears like the modern life activities are getting completely centered around the Internet.
8	Internet Applications Serving Local and Remote Users
9	Internet & Web as a delivery Vehicle
10	Increased demand for Internet applications To take advantage of opportunities presented by the Internet, businesses are continuously seeking new and innovative ways and means for offering their services via the Internet. This created a huge demand for software designers with skills to create new Internet-enabled applications or migrate existing/legacy applications on the Internet platform. Object-oriented Java technologies—Sockets, threads, RMI, clustering, Web services-- have emerged as leading solutions for creating portable, efficient, and maintainable large and complex Internet applications.
11	Elements of C-S Computing
12	Networking Basics Applications Layer Standard apps HTTP FTP Telnet User apps Transport Layer TCP UDP Programming Interface: Sockets Network Layer IP Link Layer Device drivers TCP/IP Stack
13	Networking Basics TCP (Transport Control Protocol) is a connection-oriented protocol that provides a reliable flow of data between two computers. Example applications: HTTP FTP Telnet TCP/IP Stack
14	Networking Basics UDP (User Datagram Protocol) is a protocol that sends independent packets of data, called datagrams, from one computer to another with no guarantees about arrival. Example applications: Clock server Ping TCP/IP Stack
15	Understanding Ports The TCP and UDP protocols use ports to map incoming data to a particular process running on a computer.
16	Understanding Ports Port is represented by a positive (16-bit) integer value Some ports have been reserved to support common/well known services: ftp 21/tcp telnet 23/tcp smtp 25/tcp login 513/tcp User level process/services generally use port number value >= 1024
17	Client / Server Model Relationship between two computer programs Client Initiates communication Requests services Server Receives communication Provides services Other models Master / worker Peer-to-peer (P2P)
18	Conceitos Protocolo: Padrão de comunicação entre os processos cliente e servidor.
19	Client Programming Basic steps Determine server location – IP address & port Open network connection to server Write data to server (request) Read data from server (response) Close network connection Stop client
20	Características Sockets: Cada um dos processos (Cliente e Servidor) constrói seu socket. Utiliza uma porta de comunicação.
21	Server Programming Basic steps Determine server location - port (& IP address) Create server to listen for connections Open network connection to client Read data from client (request) Write data to client (response) Close network connection to client Stop server
22	Server Programming Can support multiple connections / clients Loop Handles multiple connections in order Multithreading Allows multiple simultaneous connections
23	Client / Server Model Examples
24	TCP/IP Pilha de Protocolos Os serviços da pilha de protocolos TCP/IP podem ser arranjados de acordo com o esquema de camadas proposto pelo modelo RM/OSI da ISO, conforme figura abaixo.
25	Networking in Java Packages java.net Þ Networking java.io Þ I/O streams & utilities java.rmi Þ Remote Method Invocation java.security Þ Security policies java.lang Þ Threading classes Support at multiple levels Data transport Þ Socket classes Network services Þ URL classes Utilities & security
26	Sockets O socket de mensagens têm que ler mensagens inteiras.
27	Domínio Os domínios mais usados são o do UNIX e o da INTERNET
28	Protocolos de Comunicação Cada tipo de socket utiliza um protocolo de comunicação.
29	Usos Uma aplicação cliente que coleta informações de um usuário antes de enviá-las a um servidor central.
30	Usos Uma aplicação cliente que coleta informações de um usuário antes de enviá-las a um servidor central.
31	Networking in Java Packages java.net Þ Networking java.io Þ I/O streams & utilities java.rmi Þ Remote Method Invocation java.security Þ Security policies java.lang Þ Threading classes Support at multiple levels Data transport Þ Socket classes Network services Þ URL classes Utilities & security
32	Java Networking API Application Program Interface Set of routines, protocols, tools For building software applications Java networking API Helps build network applications Interfaces to sockets, network resources Code implementing useful functionality Includes classes for Sockets URLs
33	Java Networking Classes IP addresses InetAddress Packets DatagramPacket Sockets Socket ServerSocket DatagramSocket URLs URL
34	Java Sockets Programming Java uses BSD-style sockets to interface with TCP/IP services (java.net package) Java distinguishes between UDP, TCP server & TCP client sockets Behind-the-scenes classes do the actual work & can be updated or swapped out transparently
35	Sockets Sockets provide an interface for programming networks at the transport layer. Network communication using Sockets is very much similar to performing file I/O In fact, socket handle is treated like file handle. The streams used in file I/O operation are also applicable to socket-based I/O Socket-based communication is programming language independent. That means, a socket program written in Java language can also communicate to a program written in Java or non-Java socket program.
36	Socket Communication A server (program) runs on a specific computer and has a socket that is bound to a specific port. The server waits and listens to the socket for a client to make a connection request.
37	Socket Communication If everything goes well, the server accepts the connection. Upon acceptance, the server gets a new socket bounds to a different port. It needs a new socket (consequently a different port number) so that it can continue to listen to the original socket for connection requests while serving the connected client.
38	IP Addresses & Hostnames java.net.InetAddress class Represents a single IP address Factory class – no public constructor Performs transparent DNS lookups or reverse lookups java.net.UnkownHostException thrown if DNS system can’t find IP address for specific host
39	java.net O pacote java.net provê uma estrutura poderosa e flexível para rede. Muitas das classes deste pacote fazem parte de uma infra-estrutura de rede não utilizadas em aplicações normais, são mais complicadas e de difícil compreensão. Aqui vamos descrever somente as classes utilizadas normalmente em aplicações. A classe URL representa uma localização na Internet. Ela provê uma interface bem simples de rede – o download de um objeto referenciado por uma URL pode ser feito através de uma simples chamada, ou podem ser abertos canais de leitura ou escrita neste objeto.
40	java.net Em um nível mais complexo, o objeto URLConnection pode ser obtido a partir de um objeto URL fornecido. A classe URLConnection provê métodos adicionais que permitem trabalhar com URLs de maneiras mais sofisticadas. Para fazer mais do que um simples download de um objeto referenciado por uma URL, o pacote java.net fornece a classe Socket. Esta classe permite conectar a uma determinada porta em um determinado host Internet e ler e escrever dados utilizando as classes InputStream e OutputStream do pacote java.io. Para implementar um servidor para aceitar conexões de clientes, é possível utilizar a classe ServerSocket. Tanto a classe Socket quanto a ServerSocket utilizam a classe InetAddress, que representa um endereço Internet.
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42	Uniform Resource Locator A classe URL modela URLs, permitindo a obtenção de informações e conteúdo de páginas na Web Essa classe é parte do pacote java.net
43	URL Class Provides high-level access to network data Abstracts the notion of a connection Constructor opens network connection To resource named by URL
44	URL Constructors URL( fullURL ) URL( "http://www.cs.umd.edu/class/index.html" ) URL( baseURL, relativeURL ) URL base = new URL("http://www.cs.umd.edu/" ); URL class = new URL( base, "/class/index.html " ); URL( protocol, baseURL, relativeURL ) URL( "http", www.cs.umd.edu, "/class/index.html" ) URL( protocol, baseURL, port, relativeURL ) URL( "http", www.cs.umd.edu, 80,"/class/index.html" )
45	URL: Construtores public URL(String spec) throws MalformedURLException public URL(String protocol, String host, String file) throws MalformedURLException public URL(String protocol, String host, int port, String file) throws MalformedURLException
46	URL Methods getProtocol( ) getHost( ) getPort( ) getFile( ) getContent( ) openStream() openConnection()
47	URL: Métodos de Consulta public String getProtocol() public String getHost() public int getPort() public String getFile() public String getUserInfo() public String getPath() public String getQuery()
48	URL Connection Classes High level description of network service Access resource named by URL Can define own protocols Examples URLConnection Þ Reads resource HttpURLConnection Þ Handles web page JarURLConnection Þ Manipulates Java Archives URLClassLoader Þ Loads class file into JVM
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52	URL: Métodos de Acesso public final InputStream openStream() throws IOException public URLConnection openConnection() throws IOException
53	Exemplo de Uso de URL import java.io.; import java.net.; public class HttpClient_URL { public static void main(String[] args) throws Exception { if (args.length == 0) { System.err.println("Forneça o endereço da página."); return; } URL url = new URL(args[0]); InputStream is = url.openStream(); Reader r = new InputStreamReader(is); BufferedReader br = new BufferedReader(r); String l; while ((l = br.readLine()) != null) { System.out.println(l); } } }
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55	InetAddress Class Represents an IP address Can convert domain name to IP address Performs DNS lookup Getting an InetAddress object getLocalHost() getByName(String host) getByAddress(byte[] addr)
56	Connection Oriented TCP Protocol
57	Sockets and Java Socket Classes A socket is an endpoint of a two-way communication link between two programs running on the network. A socket is bound to a port number so that the TCP layer can identify the application that data destined to be sent. Java’s .net package provides two classes: Socket – for implementing a client ServerSocket – for implementing a server
58	Java Sockets
59	TCP Client Sockets java.net.Socket class Combines socket with socket options (timeout, linger, keep alive, no delay, etc) Encapsulates a java.io.InputStream and a java.io.OutputStream – can be retrieved for use in a layered I/O system
60	Socket Classes Provides interface to TCP, UDP sockets Socket TCP client sockets ServerSocket TCP server sockets DatagramSocket UDP sockets (server or client)
61	Socket Class Creates socket for client Constructor connects to Machine name or IP address Port number Transfer data via streams Similar to standard Java I/O streams
62	Socket Methods getInputStream() getOutputStream() close() getInetAddress() getPort() getLocalPort()
63	Implementing a Client 1. Create a Socket Object: client = new Socket( server, port_id ); 2. Create I/O streams for communicating with the server. is = new DataInputStream(client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 3. Perform I/O or communication with the server: Receive data from the server: String line = is.readLine(); Send data to the server: os.writeBytes("Hello\n"); 4. Close the socket when done: client.close();
64	A simple client (simplified code) // SimpleClient.java: a simple client program import java.net.; import java.io.; public class SimpleClient { public static void main(String args[]) throws IOException { // Open your connection to a server, at port 1234 Socket s1 = new Socket("mundroo.cs.mu.oz.au",1234); // Get an input file handle from the socket and read the input InputStream s1In = s1.getInputStream(); DataInputStream dis = new DataInputStream(s1In); String st = new String (dis.readUTF()); System.out.println(st); // When done, just close the connection and exit dis.close(); s1In.close(); s1.close(); } }
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66	TCP Server Sockets java.net.ServerSocket class Binds to a local port to listen for initial connections Can be bound to a local IP for multi-homed machines accept() method returns a java.net.Socket, not an integer descriptor
67	ServerSocket Class Create socket on server Constructor specifies local port Server listens to port Usage Begin waiting after invoking accept() Listen for connection (from client socket) Returns Socket for connection
68	ServerSocket Methods accept() close() getInetAddress() getLocalPort()
69	Implementing a Server
70	A simple server (simplified code) // SimpleServer.java: a simple server program import java.net.; import java.io.; public class SimpleServer { public static void main(String args[]) throws IOException { // Register service on port 1234 ServerSocket s = new ServerSocket(1234); Socket s1=s.accept(); // Wait and accept a connection // Get a communication stream associated with the socket OutputStream s1out = s1.getOutputStream(); DataOutputStream dos = new DataOutputStream (s1out); // Send a string! dos.writeUTF("Hi there"); // Close the connection, but not the server socket dos.close(); s1out.close(); s1.close(); } }
71	Run Run Server on mundroo.cs.mu.oz.au [raj@mundroo] java SimpleServer & Run Client on any machine (including mundroo): [raj@mundroo] java SimpleClient Hi there If you run client when server is not up: [raj@mundroo] sockets [1:147] java SimpleClient Exception in thread "main" java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:320) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:133) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:120) at java.net.Socket.<init>(Socket.java:273) at java.net.Socket.<init>(Socket.java:100) at SimpleClient.main(SimpleClient.java:6)
72	Socket Exceptions try { Socket client = new Socket(host, port); handleConnection(client); } catch(UnknownHostException uhe) { System.out.println("Unknown host: " + host); uhe.printStackTrace(); } catch(IOException ioe) { System.out.println("IOException: " + ioe); ioe.printStackTrace(); }
73	ServerSocket & Exceptions public ServerSocket(int port) throws IOException Creates a server socket on a specified port. A port of 0 creates a socket on any free port. You can use getLocalPort() to identify the (assigned) port on which this socket is listening. The maximum queue length for incoming connection indications (a request to connect) is set to 50. If a connection indication arrives when the queue is full, the connection is refused. Throws: IOException - if an I/O error occurs when opening the socket. SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
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75	Packet Oriented UDP Protocol
76	UDP Sockets java.net.DatagramSocket class Java makes no distinction between client/server for UDP sockets Connected mode UDP supported in Java 2 Can be bound to both a local port & a local IP address – multi-homed support Supports some socket options (timeout, buffer size)
77	DatagramSocket Class Create UDP socket Does not distinguish server / client sockets Constructor specifies InetAddress, port Set up UPD socket connection Send / receive DatagramPacket
78	DatagramSocket Methods close() getLocalAddress() getLocalPort() receive(DatagramPacket p) send(DatagramPacket p) setSoTimeout(int t) getSoTimeout()
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80	UDP Datagrams java.net.DatagramPacket class Expects a byte array of data Address optional for connected-mode UDP This class is final – can’t be extended! java.net.DatagramSocket instances can only send instances of java.net.DatagramPacket
81	DatagramPacket Class Each packet contains InetAddress Port of destination Data
82	DatagramPacket Class Data in packet represented as byte array
83	DatagramPacket Methods getAddress() getData() getLength() getPort() setAddress() setData() setLength() setPort()
84	Exemplo de Programa import java.io.; import java.net.; /* Este programa conecta a um WEB server e faz downloads de uma específica URL. Usa o protocolo HTTP. */ public class HttpClient { public static void main(String[] args) { try { // Verifica os argumentos if ((args.length != 1 ) && (args.length != 2)) throw new IllegalArgumentException(“Faltam argumentos”); // Pega uma string para escrever o conteúdo da URL OutputStream to_file; if (args.length == 2) to_file = new FileOutputStream( args[1] ); else to_file = System.out; // Agora usa uma class URL para analisar o que foi passado pelo // usuário como parâmetro: protocolo, host, porta, filename
85	Exemplo de Programa (cont.) URL url = new URL( args[0] ); String protocol = url.getProtocol(); if (!protocol.equals(“http”)) throw new IllegalArgumentException(“Usar o protocolo http”); String host = url.getHost(); int port = url.getPort(); if (port == -1) port = 80; // Se não há porta, // use o default do http String filename = url.getFile(); // Abrir uma conexão na rede com socket para a porta e o host // especificados Socket socket = new Socket(host,port); // Pega entrada e saída para o socket InputStream from_server = socket.getInputStream(); PrintWriter to_server = new PrintWriter ( new OutputStreamWriter(socket.getOutputStream() ));
86	Exemplo de Programa (cont.) // Envia o comando GET HTTP para o WEB server, especificando o // arquivo to_server.println(“GET “ + filename); to_server.flush(); // Envie agora // Le a resposta do server, e a escreve no arquivo byte[] buffer = new byte[4096]; int bytes_read; while(( bytes_read = from_server.read(buffer)) != -1) to_file.write(buffer, 0, bytes_read); // Quando o server fecha a conexão, nós fechamos nosso arquivo socket.close(); to_file.close(); } catch ( Exception e) { // Informe dos erros ocorridos System.err.println(e); System.err.println(“Ao usar: java HttpClient <URL> <filename>]”); } } }
87	POO-Java
88	Threading Java doesn’t support the notion of forking processes; how do we support concurrency?
89	Server in Loop: Always up // SimpleServerLoop.java: a simple server program that runs forever in a single thead import java.net.; import java.io.; public class SimpleServerLoop { public static void main(String args[]) throws IOException { // Register service on port 1234 ServerSocket s = new ServerSocket(1234); while(true) { Socket s1=s.accept(); // Wait and accept a connection // Get a communication stream associated with the socket OutputStream s1out = s1.getOutputStream(); DataOutputStream dos = new DataOutputStream (s1out); // Send a string! dos.writeUTF("Hi there"); // Close the connection, but not the server socket dos.close(); s1out.close(); s1.close(); } } }
90	Multithreaded Server: For Serving Multiple Clients Concurrently
91	POO-Java
92	Java Servlets Servlets are the Java analog to CGI Advantages of servlets: full access to other Java APIs, persistence between invocations, guaranteed portability Servlets can be generic services or specific to HTTP
93	HTTP Servlets javax.servlet.http.HttpServlet class Uses HTTP to receive requests and generate responses Full support for all HTTP methods, cookies, sessions, persistent connections Servlets can be chained – example: de-blink servlet
94	POO-Java
95	Java Applets Applets are Java programs Classes downloaded from network Run in browser on client Applets have special security restrictions Executed in applet sandbox Controlled by java.lang.SecurityManager
96	Java Applets Client-side Java programs that run in a browser Applets have special security restrictions called the applet sandbox Only applets loaded over the network are subject to the applet sandbox The applet sandbox is controlled by a java.lang.SecurityManager
97	Applet Sandbox Prevents Loading libraries Defining native methods Accessing local host file system Running other programs (Runtime.exec()) Listening for connections Opening sockets to new machines Except for originating host Restricted access to system properties
98	Applet Sandbox Can’t load libraries or define native methods Can’t access local host filesystem Can’t open sockets to hosts other than originating host Can’t use Runtime.exec() Applet windows have a unique appearance Restricted access to certain system properties
99	Applet Sandbox
100	Escaping the Applet Sandbox Browsers can define their own security policy via a new security manager Applets can be signed and executed as trusted content Security policies may vary from browser to browser, even for signed applets
101	POO-Java
102	Remote Method Invocation (RMI) RMI is the Java analog to RPC RMI servers use a naming service (rmiregistry) to register remote objects RMI servers use a special security policy implemented by RMISecurityManager The default RMI transport mechanism is via TCP sockets – this is transparent to RMI code! Any object transferred in an RMI call must implement the Serializable interface
103	Java Naming & Directory Interface (JNDI) JNDI provides a generic API that can be used to interface with any naming system JNDI uses SPIs (service provider interfaces) to access many different types of naming & directory services from the JNDI API Sun supplies JNDI SPIs for LDAP, NIS, COS (CORBA naming), RMI registry & local filesystem