Trabalhando com sockets TCP em Java
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Servidor que atende um único cliente
Um exemplo bem simples de como usar sockets TCP em Java. O servidor está apto a atender um único cliente. Tanto o cliente quanto o servidor poderão enviar mensagens texto um para o outro.
Servidor.java
package tcp;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
/**
*
* @author Emerson Ribeiro de Mello
*/
public class Servidor {
public void iniciar(int porta) {
ObjectOutputStream saida;
ObjectInputStream entrada;
boolean sair = false;
String mensagem = "";
try {
// criando um socket para ouvir na porta e com uma fila de tamanho 10
ServerSocket servidor = new ServerSocket(porta, 10);
Socket conexao;
while (!sair) {
System.out.println("Ouvindo na porta: " + porta);
//ficarah bloqueado aqui ate' alguem cliente se conectar
conexao = servidor.accept();
System.out.println("Conexao estabelecida com: " + conexao.getInetAddress().getHostAddress());
//obtendo os fluxos de entrada e de saida
saida = new ObjectOutputStream(conexao.getOutputStream());
entrada = new ObjectInputStream(conexao.getInputStream());
//enviando a mensagem abaixo ao cliente
saida.writeObject("Conexao estabelecida com sucesso...\n");
do {//fica aqui ate' o cliente enviar a mensagem FIM
try {
//obtendo a mensagem enviada pelo cliente
mensagem = (String) entrada.readObject();
System.out.println("Cliente>> " + mensagem);
saida.writeObject(mensagem);
} catch (IOException iOException) {
System.err.println("erro: " + iOException.toString());
}
} while (!mensagem.equals("FIM"));
System.out.println("Conexao encerrada pelo cliente");
sair = true;
saida.close();
entrada.close();
conexao.close();
}
} catch (Exception e) {
System.err.println("Erro: " + e.toString());
}
}
public static void main(String[] args) {
int porta = -1;
//verificando se foi informado 1 argumento de linha de comando
if (args.length < 1) {
System.err.println("Uso: java tcp.Servidor <porta>");
System.exit(1);
}
try { // para garantir que somente inteiros serao atribuidos a porta
porta = Integer.parseInt(args[0]);
} catch (Exception e) {
System.err.println("Erro: " + e.toString());
System.exit(1);
}
if (porta < 1024) {
System.err.println("A porta deve ser maior que 1024.");
System.exit(1);
}
Servidor s = new Servidor();
s.iniciar(porta);
}
}
Cliente.java
package tcp;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.util.Scanner;
/**
*
* @author Emerson Ribeiro de Mello
*/
public class Cliente {
public void iniciar(String endereco, int porta) {
ObjectOutputStream saida;
ObjectInputStream entrada;
Socket conexao;
Scanner ler = new Scanner(System.in);
String mensagem = "";
try {
conexao = new Socket(endereco, porta);
System.out.println("Conectado ao servidor " + endereco + ", na porta: " + porta);
System.out.println("Digite: FIM para encerrar a conexao");
// ligando as conexoes de saida e de entrada
saida = new ObjectOutputStream(conexao.getOutputStream());
saida.flush();
entrada = new ObjectInputStream(conexao.getInputStream());
//lendo a mensagem enviada pelo servidor
mensagem = (String) entrada.readObject();
System.out.println("Servidor>> "+mensagem);
do {
System.out.print("..: ");
mensagem = ler.nextLine();
saida.writeObject(mensagem);
saida.flush();
//lendo a mensagem enviada pelo servidor
mensagem = (String) entrada.readObject();
System.out.println("Servidor>> "+mensagem);
} while (!mensagem.equals("FIM"));
saida.close();
entrada.close();
conexao.close();
} catch (Exception e) {
System.err.println("erro: " + e.toString());
}
}
public static void main(String[] args) {
if (args.length < 2) {
System.err.println("Uso: java tcp.Cliente <endereco-IP> <porta>");
System.exit(1);
}
Cliente c = new Cliente();
c.iniciar(args[0], Integer.parseInt(args[1]));
}
}
Bate papo em modo gráfico
O exemplo a seguir faz parte do livro Java Como Programar e ilustra o uso de sockets TCP em Java para conceber uma aplicação gráfica para bate papo.
Server.java
// Fig. 21.3: Server.java
// Set up a Server that will receive a connection
// from a client, send a string to the client,
// and close the connection.
package Sockets;
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Server extends JFrame {
private JTextField enter;
private JTextArea display;
ObjectOutputStream output;
ObjectInputStream input;
public Server(){
super( "Server" );
Container c = getContentPane();
enter = new JTextField();
enter.setEnabled( false );
enter.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e ){
sendData( e.getActionCommand() );
}
}
);
c.add( enter, BorderLayout.NORTH );
display = new JTextArea();
c.add( new JScrollPane( display ),
BorderLayout.CENTER );
setSize( 300, 150 );
show();
}
public void runServer(){
ServerSocket server;
Socket connection;
int counter = 1;
try {
// Step 1: Create a ServerSocket.
server = new ServerSocket( 5050, 100 );
while ( true ) {
// Step 2: Wait for a connection.
display.setText( "Waiting for connection\n" );
connection = server.accept();
display.append( "Connection " + counter + " received from: " +
connection.getInetAddress().getHostName() );
// Step 3: Get input and output streams.
output = new ObjectOutputStream(connection.getOutputStream() );
output.flush();
input = new ObjectInputStream(connection.getInputStream() );
display.append( "\nGot I/O streams\n" );
// Step 4: Process connection.
String message = "SERVER>>> Connection successful";
output.writeObject( message );
output.flush();
enter.setEnabled( true );
do {
try {
message = (String) input.readObject();
display.append( "\n" + message );
display.setCaretPosition(display.getText().length() );
}catch ( ClassNotFoundException cnfex ) {
display.append("\nUnknown object type received" );
}
} while ( !message.equals( "CLIENT>>> TERMINATE" ) );
// Step 5: Close connection.
display.append( "\nUser terminated connection" );
enter.setEnabled( false );
output.close();
input.close();
connection.close();
++counter;
}
}catch ( EOFException eof ) {
System.out.println( "Client terminated connection" );
}catch ( IOException io ) {
io.printStackTrace();
}
}
private void sendData( String s ){
try {
output.writeObject( "SERVER>>> " + s );
output.flush();
display.append( "\nSERVER>>>" + s );
}catch ( IOException cnfex ) {
display.append("\nError writing object" );
}
}
public static void main( String args[] ){
Server app = new Server();
app.addWindowListener(
new WindowAdapter() {
public void windowClosing( WindowEvent e ){
System.exit( 0 );
}
}
);
app.runServer();
}
}
/**************************************************************************
* (C) Copyright 1999 by Deitel & Associates, Inc. and Prentice Hall. *
* All Rights Reserved. *
* *
* DISCLAIMER: The authors and publisher of this book have used their *
* best efforts in preparing the book. These efforts include the *
* development, research, and testing of the theories and programs *
* to determine their effectiveness. The authors and publisher make *
* no warranty of any kind, expressed or implied, with regard to these *
* programs or to the documentation contained in these books. The authors *
* and publisher shall not be liable in any event for incidental or *
* consequential damages in connection with, or arising out of, the *
* furnishing, performance, or use of these programs. *
*************************************************************************/
Client.java
// Fig. 21.4: Client.java
// Set up a Client that will read information sent
// from a Server and display the information.
package Sockets;
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Client extends JFrame {
private JTextField enter;
private JTextArea display;
ObjectOutputStream output;
ObjectInputStream input;
String message = "";
public Client(){
super( "Client" );
Container c = getContentPane();
enter = new JTextField();
enter.setEnabled( false );
enter.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent e ){
sendData( e.getActionCommand() );
}
}
);
c.add( enter, BorderLayout.NORTH );
display = new JTextArea();
c.add( new JScrollPane( display ), BorderLayout.CENTER );
setSize( 300, 150 );
show();
}
public void runClient(){
Socket client;
try {
// Step 1: Create a Socket to make connection.
display.setText( "Attempting connection\n" );
client = new Socket(InetAddress.getByName( "127.0.0.1" ), 5050 );
display.append( "Connected to: " + client.getInetAddress().getHostName() );
// Step 2: Get the input and output streams.
output = new ObjectOutputStream(client.getOutputStream() );
output.flush();
input = new ObjectInputStream(client.getInputStream() );
display.append( "\nGot I/O streams\n" );
// Step 3: Process connection.
enter.setEnabled( true );
do {
try {
message = (String) input.readObject();
display.append( "\n" + message );
display.setCaretPosition(display.getText().length() );
}catch ( ClassNotFoundException cnfex ) {
display.append("\nUnknown object type received" );
}
} while ( !message.equals( "SERVER>>> TERMINATE" ) );
// Step 4: Close connection.
display.append( "Closing connection.\n" );
output.close();
input.close();
client.close();
}catch ( EOFException eof ) {
System.out.println( "Server terminated connection" );
}catch ( IOException e ) {
e.printStackTrace();
}
}
private void sendData( String s ){
try {
message = s;
output.writeObject( "CLIENT>>> " + s );
output.flush();
display.append( "\nCLIENT>>>" + s );
}catch ( IOException cnfex ) {
display.append("\nError writing object" );
}
}
public static void main( String args[] ){
Client app = new Client();
app.addWindowListener(
new WindowAdapter() {
public void windowClosing( WindowEvent e ){
System.exit( 0 );
}
}
);
app.runClient();
}
}
/**************************************************************************
* (C) Copyright 1999 by Deitel & Associates, Inc. and Prentice Hall. *
* All Rights Reserved. *
* *
* DISCLAIMER: The authors and publisher of this book have used their *
* best efforts in preparing the book. These efforts include the *
* development, research, and testing of the theories and programs *
* to determine their effectiveness. The authors and publisher make *
* no warranty of any kind, expressed or implied, with regard to these *
* programs or to the documentation contained in these books. The authors *
* and publisher shall not be liable in any event for incidental or *
* consequential damages in connection with, or arising out of, the *
* furnishing, performance, or use of these programs. *
*************************************************************************/