Streams - web.fe.up.ptrcamacho/cadeiras/cpa/acetatos/streams-2.pdf · Escrita em Ficheiro { exemplo...

Apresenta�c~aoJava { conceitos B�asicosJava { t�opicos espec��cos

Streams

I StreamsI Streams de entrada/sa��daI Streams para acesso a �cheirosI socketsI �ltrosI serializa�c~ao de objectosI exemplos

Rui Camacho Complementos de Programa�c~ao e Algoritmos { LEICApresenta�c~ao

Java { conceitos B�asicosJava { t�opicos espec��cos

Streams

Abstrac�c~ao do Java para tratar qualquer fonte ou destino de dados e que�e independente de dispositivos f��sicos concretos. A leitura/escrita emstreams �e sequencial. Uma stream funciona como a liga�c~ao a um canal decomunica�c~ao para qualquer dispositivo (disco, teclado, ecr~a, rede, etc)

Tipos:I streams de caracteres, ou streams de textoI streams de byte, ou streams bin�arias

Utiliza�c~ao:I input streams | leitura de dadosI output streams | escrita de dados

Rui Camacho Complementos de Programa�c~ao e Algoritmos { LEIC


Streams em Java

de \Advanced Java Networking", Prashant Sridharan



Streams em Java

de \Java Network Programming, M. Hughes et al.



Streams em Java

de \Java Network Programming, M. Hughes et al.



Streams

{ classes de java.io {

Classes de E/S usando streams s~ao subclasses das classesabstractas da package java.io:

I InputStream | leitura de byte

I OutputStreams | escrita de byte

I Reader | leitura de caracteres

I Writer | escrita de caracteres



Classes da package java.io

de \POO em JAVA", F. M�ario Martins



Leitura do teclado { exemplo

public class Consola f

public static String leStr() f // le uma Stringint ch;String r = "";

while (true) ftry fch = System.in.read();if (ch < 0 jj ch == 27 jj ch == 13 jj ch == 10)f //ESC ou CRif (ch == 27) f // se for ESC tem que consumir o CR/LF !!ch = System.in.read();ch = System.in.read();

g// if (ch == 13) // se for CR tem que consumir o LF !!// ch = System.in.read();

return r;gelse r = r + (char) ch;gcatch(java.io.IOException e) freturn r;g

gg




Leitura do teclado (cont.)

public static int leInt() f // le um inteirowhile(true)f

tryfreturn Integer.valueOf(leStr().trim()).intValue();

gcatch(NumberFormatException e)f System.out.println("Nao e um numero inteiro !!"); g

gg

public static double leDouble() f // le um Doublewhile(true)f

tryfreturn Double.valueOf(leStr().trim()).doubleValue();

gcatch(NumberFormatException e)f System.out.println("Nao e um numero em VF !!"); g

gg

de \POO em JAVA", F. M�ario MartinsRui Camacho Complementos de Programa�c~ao e Algoritmos { LEICApresenta�c~ao


Leitura do teclado (cont.)

// le um booleano

public static boolean leBool() fwhile(true)ftryfString s = leStr().trim().toLowerCase();if ( s.equals("true") jj s.equals("false"))return Boolean.valueOf(s).booleanValue();elsethrow new IllegalArgumentException("");

gcatch(IllegalArgumentException e)

f System.out.println("Nao e um Booleano "); gg

gg




Leitura de Ficheiro | leitura de inteiros

import java.io.*;

public class LerDeFicheiro fprivate Bu�eredReader �cheiro;private String linha;

public void leDeFicheiro(String NomeDoFicheiro)f

try f�cheiro = new Bu�eredReader(new FileReader(NomeDoFicheiro));while(true)flinha = �cheiro.readLine();if(linha == null)f�cheiro.close();break;

gSystem.out.println("LINHA: "+linha);g

gcatch (FileNotFoundException e) fSystem.out.println("Ficheiro "+NomeDoFicheiro+" nao existe");

gcatch(IOException e)fSystem.out.println("ERRO na leitura do �cheiro");

ggg



Escrita em Ficheiro { exemplo

package chapman.io;import java.io.*;import chapman.io.Fmt;

public class FileOut fprivate PrintWriter out; // referencia para PrintWriterpublic �nal int WRITE OK = 0; // escrita com sucessopublic �nal int IO EXCEPTION = -999; // excepcao de E/Spublic int writeStatus; // estado da operacao de escrita

public FileOut(String �leName)ftryf out = new PrintWriter(new Bu�eredWriter(new FileWriter(�leName,false)));gcatch (IOException e) fwriteStatus = IO EXCEPTION;g

g

public FileOut(String �leName, boolean append)ftryf out = new PrintWriter(new Bu�eredWriter( new FileWriter(�leName,append)));gcatch(IOException e)f writeStatus = IO EXCEPTION;g

g

//usage: out.printf("Time = %8.2f snn",time);public void printf(String fmt, double x) fout.print(Fmt.sprintf(fmt,x));writeStatus = WRITE OK;

gde \Java for Engineers and Scientists", S. J. Chapman



Escrita em Ficheiro { exemplo II {

//usage: out.printf("string = %snn",s);public void printf(String fmt, String s) fout.print(Fmt.sprintf(fmt,s));writeStatus = WRITE OK;

gpublic void close() fout.close(); // fecha o �cheiro de entrada

g

protected void �nalize() ftry fout.close();super.�nalize();

gcatch(Throwable e)f System.out.println("Throwable");g

gg

de \Java for Engineers and Scientists", S. J. Chapman



classe File

(java.io)

N~ao �e uma stream. Disponibiliza m�etodos para as habituaisopera�c~oes sobre �cheiros e direct�oriosI isFile() | testar se �e �cheiroI isDirectory() | veri�car se �e direct�orioI getPath() | caminho at�e ao direct�orio do �cheiroI length | tamanho do �cheiroI delete() | remover o �cheiroI renameTo() | mudar o nomeI list() | listar direct�orio



Sockets: exemplo de um servidor

import java.net.*;import java.io.*;

class Servidor fstatic int porta = 1234;

public static void main(String args[]) fServerSocket server;Socket socket;DataInputStream input;PrintStream output;String line;

try f server = new ServerSocket(porta); gcatch(Exception e) f System.err.println(\Nao posso ouvir a porta \+porta); return; gwhile(true) ftry fsocket = server.accept();input = new DataInputStream(socket.getInputStream());output = new PrintStream(socket.getOutputStream()); gcatch(IOException e) f System.err.println(\Erro na criacao do socketnn"+e.getMessage()); break; gtry f line = input.readLine(); gcatch(IOException e) f System.err.println("Erro na leitura do socket");output.close();continue; goutput.print(\Recebi:nn|nn"+line+"nn|");output.close();

ggg Rui Camacho Complementos de Programa�c~ao e Algoritmos { LEIC


Sockets: exemplo de um cliente

import java.net.*;import java.io.*;

class Cliente fstatic String maquina = "localhost";static int porta = 1234;

public static void main(String arg[]) fSocket socket;DataInputStream input;PrintStream output;String line;

try f socket = new Socket(maquina,porta);gcatch(Exception e) fSystem.err.println(\Err porta \+porta+" em \+maquina); return; g

try finput = new DataInputStream(socket.getInputStream());output = new PrintStream(socket.getOutputStream());

gcatch(Exception e) f System.err.println(\Falhou ligacao"); return; gfor(int i=0; i < arg.length; i++) output.print(arg[i]+" ");output.println("");output. ush();try fwhile((line=input.readLine()) != null) System.out.println(line);

gcatch(Exception e) f System.err.println(\Erro I/0"); return; g

gg Rui Camacho Complementos de Programa�c~ao e Algoritmos { LEIC


Con�gura�c~oes t��picas de streams para E-S

import java.io.*;

public class IOStreamDemo fpublic static void main(String[] args)throws IOException f// 1. Reading input by lines:Bu�eredReader in = new Bu�eredReader(new FileReader("IOStreamDemo.java"));String s, s2 = new String();while((s = in.readLine())!= null)s2 += s + "nn";in.close();

// 1b. Reading standard input:Bu�eredReader stdin = new Bu�eredReader(new InputStreamReader(System.in));System.out.print("Enter a line:");System.out.println(stdin.readLine());

// 2. Input from memoryStringReader in2 = new StringReader(s2);int c;while((c = in2.read()) != -1)System.out.print((char)c);

// 3. Formatted memory inputtry fDataInputStream in3 = new DataInputStream( new ByteArrayInputStream(s2.getBytes()));while(true) System.out.print((char)in3.readByte());

gcatch(EOFException e)fSystem.err.println("Eof stream"); g

de \'Thinking in Java", Bruce EckelRui Camacho Complementos de Programa�c~ao e Algoritmos { LEICApresenta�c~ao



// 4. File outputtry fBu�eredReader in4 = new Bu�eredReader(new StringReader(s2));PrintWriter out1 = new PrintWriter( new Bu�eredWriter(new FileWriter("IO.out")));int lineCount = 1;while((s = in4.readLine()) != null )out1.println(lineCount++ + ": " + s);out1.close();g

catch(EOFException e)fSystem.err.println("Eof stream");g

// 5. Storing & recovering datatry fDataOutputStream out2 = new DataOutputStream( new Bu�eredOutputStream(new FileOutputStream("Data.txt")));out2.writeDouble(3.14159);out2.writeUTF("That was pi");out2.writeDouble(1.41413);out2.writeUTF("Square root of 2");out2.close();DataInputStream in5 = new DataInputStream(new Bu�eredInputStream( new FileInputStream("Data.txt")));// Must use DataInputStream for data:System.out.println(in5.readDouble());// Only readUTF() will recover the Java-UTF String properly:System.out.println(in5.readUTF());// Read the following double and String:System.out.println(in5.readDouble());System.out.println(in5.readUTF());g

catch(EOFException e)fSystem.err.println("Eof stream");gde \'Thinking in Java", Bruce EckelRui Camacho Complementos de Programa�c~ao e Algoritmos { LEIC



// 6. Reading/writing random access �lesRandomAccessFile rf = new RandomAccessFile("rtest.dat", "rw");for(int i = 0; i < 10; i++)rf.writeDouble(i*1.414);rf.close();

rf = new RandomAccessFile("rtest.dat", "rw");rf.seek(5*8);rf.writeDouble(47.0001);rf.close();

rf = new RandomAccessFile("rtest.dat", "r");for(int i = 0; i < 10; i++)System.out.println("Value " + i + ": " +

rf.readDouble());rf.close();g

g

de \'Thinking in Java", Bruce EckelRui Camacho Complementos de Programa�c~ao e Algoritmos { LEICApresenta�c~ao


Compress~ao de �cheiros usando GZIP

import java.util.zip.*;public class GZIPcompress fpublic static void main(String[] args)throws IOException fBu�eredReader in = new Bu�eredReader(new FileReader(args[0]));Bu�eredOutputStream out = new Bu�eredOutputStream(new GZIPOutputStream(

new FileOutputStream("test.gz")));System.out.println("Writing �le");int c;while((c = in.read()) != -1) out.write(c);in.close();out.close();System.out.println("Reading �le");Bu�eredReader in2 = new Bu�eredReader(new InputStreamReader(new GZIPInputStream(

new FileInputStream("test.gz"))));String s;while((s = in2.readLine()) != null)System.out.println(s);

gg

de \'Thinking in Java", Bruce Eckel



Serializa�c~ao de objectos

I Permite o armazenamento e recupera�c~ao de objectos em �cheiros.I Permite enviar e receber objectos atrav�es de uma linha de comunica�c~ao.

Implementa�c~ao de persistencia de objectos.I Usado, por exemplo, em RMI para enviar objectos a m�etodos remotos.I Os objectos s~ao codi�cados numa sequencia de caracteres.I �E guardada a estrutura da classe juntamente com os valores dos seus

membros.I Quando h�a liga�c~oes a outros objectos as rotinas de serializa�c~ao

automaticamente serializam os objectos referidos no objecto a serializar.I S~ao evitados ciclos de referencias entre objectos




EscritaI classe ObjectOutputStreamI m�etodo writeObject

LeituraI classe ObjectInputStreamI m�etodo readObject

I Caso a aplica�c~ao queira aplicar encripta�c~ao tem que sobrepor os m�etodosde escrita e leitura.

I usar private transient class ... quando n~ao queremos a serializa�c~ao de umobjecto. Ou ent~ao lan�car uma NoAccessException




import java.io.*;

class Data implements Serializable fprivate int i;Data(int x) f i = x; gpublic String toString() freturn Integer.toString(i);

gg

public class Worm implements Serializable f// Generate a random int value:private static int r() freturn (int)(Math.random() * 10);

gprivate Data[] d = fnew Data(r()), new Data(r()), new Data(r())g;private Worm next;private char c;

// Value of i == number of segmentsWorm(int i, char x) fSystem.out.println(" Worm constructor: " + i);c = x;if({i > 0) next = new Worm(i, (char)(x + 1));

gWorm() fSystem.out.println("Default constructor");gpublic String toString() fString s = ":" + c + "(";for(int i = 0; i < d.length; i++) s += d[i].toString();s += ")";

if(next != null) s += next.toString();return s;

g





public static void main(String[] args) throws ClassNotFoundException, IOException fWorm w = new Worm(6, 'a');

System.out.println("w = " + w);ObjectOutputStream out = new ObjectOutputStream( new FileOutputStream("worm.out"));out.writeObject("Worm storage");out.writeObject(w);out.close(); // Also ushes output

ObjectInputStream in = new ObjectInputStream( new FileInputStream("worm.out"));String s = (String)in.readObject();Worm w2 = (Worm)in.readObject();System.out.println(s + ", w2 = " + w2);

ByteArrayOutputStream bout = new ByteArrayOutputStream();ObjectOutputStream out2 = new ObjectOutputStream(bout);out2.writeObject("Worm storage");out2.writeObject(w);out2. ush();

ObjectInputStream in2 = new ObjectInputStream( new ByteArrayInputStream(bout.toByteArray()));s = (String)in2.readObject();Worm w3 = (Worm)in2.readObject();System.out.println(s + ", w3 = " + w3);

gg




Poss��vel resultado

Worm constructor: 6Worm constructor: 5Worm constructor: 4Worm constructor: 3Worm constructor: 2Worm constructor: 1w = :a(262) :b(100) :c(396) :d(480) :e(316) :f(398)Worm storage, w2 = :a(262) :b(100) :c(396) :d(480) :e(316) :f(398)Worm storage, w3 = :a(262) :b(100) :c(396) :d(480) :e(316) :f(398)



Streams - web.fe.up.ptrcamacho/cadeiras/cpa/acetatos/streams-2.pdf · Escrita em Ficheiro { exemplo...

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