• Pagina inicial
  • Artigos
  • Em geral
  • Java NIO (E/S sem bloqueio) com exemplo de servidor-cliente – java.nio.ByteBuffer e channels.Selector – Java NIO Vs. IO

Java NIO (E/S sem bloqueio) com exemplo de servidor-cliente – java.nio.ByteBuffer e channels.Selector – Java NIO Vs. IO

Publicados: 2021-08-06
Java NIO (I:O sem bloqueio) com exemplo de servidor-cliente - CrunchifyNIOServer.java

Java NIO é meu tópico favorito. Eu tenho trabalhado com o NIO desde os últimos 2 anos e gostaria de compartilhar um Server-Client code para meus leitores que estão livres para usar este código em seu ambiente de produção.

A partir do JDK 1.4, o NIO foi criado para permitir que todos os programadores Java implementassem entrada/saída de alta velocidade sem ter que lidar com código nativo personalizado. O NIO usa a biblioteca java.nio.buffer em comparação com a E/S simples que drena e preenche o buffer internamente de qualquer sistema operacional.

Neste tutorial, veremos as bibliotecas java.nio.channels e java.nio.channels.Selector .

  • os channels representam conexões com entidades capazes de realizar operações de E/S, como arquivos e soquetes; define seletores , para operações de E/S multiplexadas e sem bloqueio.
  • selector pode ser criado invocando o open method desta classe, que usará o provedor de seletor padrão do sistema para criar um novo seletor.
Explicação do pacote java.nio com detalhes da API

Se você tem below questions então você está no lugar certo:

  • Como começar com Java NIO
  • O que são os tutoriais Java NIO e Java NIO
  • Java assíncrono NIO
  • Qual é o uso exato do pacote java nio
  • Tutorial Java NIO
  • Como implementar E/S de alto desempenho com Java NIO

Vamos começar:

Passo 1

  • Crie CrunchifyNIOServer.java que abre a conexão na port 1111
  • use isAcceptable() para verificar se o canal está pronto para aceitar uma nova conexão de soquete
    • Se sim - conecte-o
  • use isReadable() para verificar se o canal está pronto para leitura
    • se sim – leia do buffer e imprima no console do Eclipse
  • Depois de obter o sobrenome da empresa “crunchify”
    • conexão próxima

Passo 2

  • Crie CrunchifyNIOClient.java que tenta se conectar ao servidor na port 1111
  • Criar ArrayList com 5 nomes de empresas
  • Iterar por ArrayList e enviar cada companyName para o servidor
  • Fechar a conexão após o término da tarefa

Dê uma olhada neste código Java:

Código do servidor – CrunchifyNIOServer.java

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
package crunchify . com . tutorials ;
 
import java . io . IOException ;
import java . net . InetSocketAddress ;
import java . nio . ByteBuffer ;
import java . nio . channels . SelectionKey ;
import java . nio . channels . Selector ;
import java . nio . channels . ServerSocketChannel ;
import java . nio . channels . SocketChannel ;
import java . util . Iterator ;
import java . util . Set ;
 
/**
* @author Crunchify.com
* Java NIO (Non-blocking I/O) with Server-Client Example - java.nio.ByteBuffer and channels.Selector
* This is CrunchifyNIOServer.java
*/
 
public class CrunchifyNIOServer {
 
@ SuppressWarnings ( "unused" )
public static void main ( String [ ] args ) throws IOException {
 
// Selector: A multiplexor of SelectableChannel objects.
// A selector may be created by invoking the open method of this class, which will use the system's default selector provider to create a new selector.
// A selector may also be created by invoking the openSelector method of a custom selector provider. A selector remains open until it is closed via its close method.
Selector selector = Selector . open ( ) ; // selector is open here
 
// ServerSocketChannel: A selectable channel for stream-oriented listening sockets.
// A server-socket channel is created by invoking the open method of this class.
// It is not possible to create a channel for an arbitrary, pre-existing ServerSocket.
ServerSocketChannel crunchifySocket = ServerSocketChannel . open ( ) ;
// InetSocketAddress: This class implements an IP Socket Address (IP address + port number) It can also be a pair (hostname + port number),
// in which case an attempt will be made to resolve the hostname.
// If resolution fails then the address is said to be unresolved but can still be used on some circumstances like connecting through a proxy.
InetSocketAddress crunchifyAddr = new InetSocketAddress ( "localhost" , 1111 ) ;
 
// Binds the channel's socket to a local address and configures the socket to listen for connections
crunchifySocket . bind ( crunchifyAddr ) ;
 
// Adjusts this channel's blocking mode.
crunchifySocket . configureBlocking ( false ) ;
 
int ops = crunchifySocket . validOps ( ) ;
// SelectionKey: A token representing the registration of a SelectableChannel with a Selector.
// A selection key is created each time a channel is registered with a selector.
// A key remains valid until it is cancelled by invoking its cancel method, by closing its channel, or by closing its selector.
SelectionKey selectKy = crunchifySocket . register ( selector , ops , null ) ;
 
// Infinite loop..
// Keep server running
while ( true ) {
 
log ( "I'm a server and I'm waiting for new connection and buffer select..." ) ;
// Selects a set of keys whose corresponding channels are ready for I/O operations
selector . select ( ) ;
 
// token representing the registration of a SelectableChannel with a Selector
Set < SelectionKey > crunchifyKeys = selector . selectedKeys ( ) ;
Iterator < SelectionKey > crunchifyIterator = crunchifyKeys . iterator ( ) ;
 
while ( crunchifyIterator . hasNext ( ) ) {
SelectionKey myKey = crunchifyIterator . next ( ) ;
 
// Tests whether this key's channel is ready to accept a new socket connection
if ( myKey . isAcceptable ( ) ) {
SocketChannel crunchifyClient = crunchifySocket . accept ( ) ;
 
// Adjusts this channel's blocking mode to false
crunchifyClient . configureBlocking ( false ) ;
 
// Operation-set bit for read operations
crunchifyClient . register ( selector , SelectionKey . OP_READ ) ;
log ( "Connection Accepted: " + crunchifyClient . getLocalAddress ( ) + "\n" ) ;
 
// Tests whether this key's channel is ready for reading
} else if ( myKey . isReadable ( ) ) {
SocketChannel crunchifyClient = ( SocketChannel ) myKey . channel ( ) ;
// ByteBuffer: A byte buffer.
// This class defines six categories of operations upon byte buffers:
// Absolute and relative get and put methods that read and write single bytes;
// Absolute and relative bulk get methods that transfer contiguous sequences of bytes from this buffer into an array;
ByteBuffer crunchifyBuffer = ByteBuffer . allocate ( 256 ) ;
crunchifyClient . read ( crunchifyBuffer ) ;
String result = new String ( crunchifyBuffer . array ( ) ) . trim ( ) ;
 
log ( "Message received: " + result ) ;
 
if ( result . equals ( "Crunchify.com" ) ) {
crunchifyClient . close ( ) ;
log ( "\nIt's time to close connection as we got last company name 'Crunchify'" ) ;
log ( "\nServer will keep running. Try running client again to establish new connection" ) ;
}
}
crunchifyIterator . remove ( ) ;
}
}
}
 
private static void log ( String str ) {
System . out . println ( str ) ;
}
}
 

Código do cliente – CrunchifyNIOClient.java

Java NIO (I:O sem bloqueio) com exemplo de servidor-cliente - CrunchifyNIOClient.java
Java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
package crunchify . com . tutorials ;
 
import java . io . IOException ;
import java . net . InetSocketAddress ;
import java . nio . ByteBuffer ;
import java . nio . channels . SocketChannel ;
import java . util . ArrayList ;
 
/**
* @author Crunchify.com
* Java NIO (Non-blocking I/O) with Server-Client Example - java.nio.ByteBuffer and channels.Selector
* This is CrunchifyNIOClient.java
*/
 
public class CrunchifyNIOClient {
 
public static void main ( String [ ] args ) throws IOException , InterruptedException {
 
InetSocketAddress crunchifyAddr = new InetSocketAddress ( "localhost" , 1111 ) ;
//  selectable channel for stream-oriented connecting sockets
SocketChannel crunchifyClient = SocketChannel . open ( crunchifyAddr ) ;
 
log ( "Connecting to Server on port 1111..." ) ;
 
ArrayList <String> companyDetails = new ArrayList <String> ( ) ;
 
// create a ArrayList with companyName list
companyDetails . add ( "Facebook" ) ;
companyDetails . add ( "Twitter" ) ;
companyDetails . add ( "IBM" ) ;
companyDetails . add ( "Google" ) ;
companyDetails . add ( "Crunchify" ) ;
 
for ( String companyName : companyDetails ) {
 
byte [ ] message = new String ( companyName ) . getBytes ( ) ;
ByteBuffer buffer = ByteBuffer . wrap ( message ) ;
crunchifyClient . write ( buffer ) ;
 
log ( "sending: " + companyName ) ;
buffer . clear ( ) ;
 
// wait for 2 seconds before sending next message
Thread . sleep ( 2000 ) ;
}
// close(): Closes this channel.
// If the channel has already been closed then this method returns immediately.
// Otherwise it marks the channel as closed and then invokes the implCloseChannel method in order to complete the close operation.
crunchifyClient . close ( ) ;
}
 
private static void log ( String str ) {
System . out . println ( str ) ;
}
}

Resultado no lado do servidor:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
I 'm a server and I' m waiting for new connection and buffer select . . .
Connection Accepted : / 127.0.0.1 : 1111
 
I 'm a server and <meta charset="utf-8"/>I' m waiting for new connection and buffer select . . .
Message received : Facebook
< meta charset = "utf-8" / > I 'm a server and <meta charset="utf-8"/>I' m waiting for new connection and buffer select . . .
Message received : Twitter
< meta charset = "utf-8" / > I 'm a server and <meta charset="utf-8"/>I' m waiting for new connection and buffer select . . .
Message received : IBM
< meta charset = "utf-8" / > I 'm a server and <meta charset="utf-8"/>I' m waiting for new connection and < a href = "https://crunchify.com/how-to-remove-duplicate-elements-from-csv-or-any-other-file-in-java/" target = "_blank" rel = "noreferrer noopener" > buffer < / a > select . . .
Message received : Google
< meta charset = "utf-8" / > I 'm a server and <meta charset="utf-8"/>I' m waiting for new connection and buffer select . . .
Message received : Crunchify
 
It 's time to <a href="https://crunchify.com/json-manipulation-in-java-examples/" target="_blank" rel="noreferrer noopener">close connection</a> as we got last company name ' Crunchify '
 
Server will keep running. Try running client again to establish new connection
<meta charset="utf-8"/>I' m a server and < meta charset = "utf-8" / > I ' m waiting for new connection and buffer select . . .

Resultado no lado do cliente:

1
2
3
4
5
6
Connecting to Server on port 1111...
sending : Facebook
sending : Twitter
sending : IBM
sending : Google
sending : Crunchify

Algumas perguntas frequentes:

  1. Do cliente, como mantenho uma conexão persistente?
    • Você pode usar socket.setKeepAlive(true); ter conexões vivas do lado do cliente.
  2. Como leio uma resposta à mensagem que envio ao servidor. O servidor continua gerando mensagens a cada 10 segundos. Eu só preciso ler a resposta ao meu pedido. Pelo que entendi, o TCP “transmite” dados em vez de fim de registro, etc.
    • Para comunicação cliente-servidor, um protocolo precisa ser bem definido. A chamada readLine() será bloqueada até que todos os dados sejam retornados, portanto, não a use. Try reading bytes from the stream until -1 is returned.

Deixe-me saber se isso funciona.