Java NIO (E/S sin bloqueo) con ejemplo de servidor-cliente: java.nio.ByteBuffer y canales. Selector: Java NIO vs. io

Publicado: 2021-08-06
Java NIO (E/S sin bloqueo) con ejemplo de servidor-cliente - CrunchifyNIOServer.java

Java NIO es mi tema favorito. He estado trabajando con NIO desde los últimos 2 años y me gustaría compartir un Server-Client code simple para mis lectores que pueden usar este código en su entorno de producción.

A partir de JDK 1.4, NIO se creó para permitir que todos los programadores de Java implementen entradas/salidas de muy alta velocidad sin tener que lidiar con código nativo personalizado. NIO usa la biblioteca java.nio.buffer en comparación con E/S simple que drena y llena el búfer internamente en cualquier sistema operativo.

En este tutorial repasaremos las bibliotecas java.nio.channels y java.nio.channels.Selector .

  • channels representan conexiones a entidades que son capaces de realizar operaciones de E/S, como archivos y sockets; define selectores , para operaciones de E/S multiplexadas y sin bloqueo.
  • El selector se puede crear invocando el open method de esta clase, que utilizará el proveedor de selector predeterminado del sistema para crear un nuevo selector.
Explicación del paquete java.nio con detalles de la API

Si tiene las below questions , entonces está en el lugar correcto:

  • Cómo empezar con Java NIO
  • Qué es Java NIO y Tutoriales de Java NIO
  • Java NIO asíncrono
  • ¿Cuál es el uso exacto del paquete java nio?
  • Tutorial Java NIO
  • Cómo implementar E/S de alto rendimiento con Java NIO

Empecemos:

Paso 1

  • Cree CrunchifyNIOServer.java que abre la conexión en el port 1111
  • use isAcceptable() para verificar si el canal está listo para aceptar una nueva conexión de socket
    • Si es así, conéctelo
  • use isReadable() para verificar si el canal está listo para leer
    • en caso afirmativo, lea del búfer e imprima en la consola de Eclipse
  • Una vez que obtenga el apellido de la empresa "crunchify"
    • conexión cercana

Paso 2

  • Cree CrunchifyNIOClient.java que intenta conectarse al servidor en el port 1111
  • Crear ArrayList con 5 nombres de empresas
  • Iterar a través de ArrayList y enviar cada nombre de empresa al servidor
  • Cerrar conexión después de finalizar la tarea

Echa un vistazo a este código Java:

Código del servidor: CrunchifyNIOServer.java

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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 de cliente – CrunchifyNIOClient.java

Java NIO (E/S sin bloqueo) con ejemplo de servidor-cliente - CrunchifyNIOClient.java
Java
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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 en el lado del servidor:

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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 en el lado del cliente:

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Connecting to Server on port 1111...
sending : Facebook
sending : Twitter
sending : IBM
sending : Google
sending : Crunchify

Algunas preguntas frecuentes:

  1. Desde el cliente, ¿cómo mantengo una conexión persistente?
    • Podrías usar socket.setKeepAlive(true); tener conexiones vivas desde el lado del cliente.
  2. ¿Cómo leo una respuesta al mensaje que envío al servidor? El servidor sigue generando mensajes cada 10 segundos. Solo necesito leer la respuesta a mi solicitud. Por lo que entiendo, TCP "transmite" datos en lugar de fin de registro, etc.
    • Para la comunicación entre el servidor y el cliente, es necesario definir bien un protocolo. La llamada readLine() se bloqueará hasta que se devuelvan todos los datos, así que no la use. Try reading bytes from the stream until -1 is returned.

Déjame saber si eso funciona.