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  • Java NIO (Non-blocking I/O) with Server-Client Example – java.nio.ByteBuffer 和 channels.Selector – Java NIO Vs. IO

Java NIO (Non-blocking I/O) with Server-Client Example – java.nio.ByteBuffer 和 channels.Selector – Java NIO Vs. IO

已发表: 2021-08-06
带有服务器-客户端示例的 Java NIO（非阻塞 I:O） - CrunchifyNIOServer.java

Java NIO是我最喜欢的话题。 自过去 2 年以来，我一直在与 NIO 合作，我想为我的读者分享简单Server-Client code ，他们可以在他们的生产环境中免费使用这些代码。

从 JDK 1.4 开始，创建 NIO 是为了允许所有 Java 程序员实现非常高速的输入/输出，而无需处理自定义的本机代码。 NIO 使用java.nio.buffer库与简单的 I/O 相比，后者在任何操作系统内部耗尽和填充缓冲区。

在本教程中，我们将java.nio.channels和java.nio.channels.Selector库。

  • channels表示与能够执行 I/O 操作的实体的连接，例如文件和套接字； 定义 selectors ，用于多路复用的非阻塞 I/O 操作。
  • 可以通过调用该类的open method来创建selector ，该方法将使用系统默认的选择器提供程序来创建一个新的选择器。
带有 API 详细信息的 java.nio 包说明

如果您有below questions ，那么您来对地方了：

  • 如何开始使用 Java NIO
  • 什么是Java NIO和Java NIO教程
  • 异步 Java NIO
  • java nio包的具体用途是什么
  • Java NIO 教程
  • 如何使用 Java NIO 实现高性能 I/O

让我们开始吧：

第1步

  • 创建CrunchifyNIOServer.java在port 1111上打开连接
  • 使用isAcceptable()检查通道是否准备好接受新的套接字连接
    • 如果是 - 连接它
  • 使用isReadable()检查通道是否准备好读取
    • 如果是 - 从缓冲区读取并在 Eclipse 控制台上打印
  • 一旦你得到最后的公司名称“crunchify”
    • 紧密连接

第2步

  • 创建CrunchifyNIOClient.java尝试连接到port 1111上的服务器
  • 使用 5 个公司名称创建 ArrayList
  • 遍历 ArrayList 并将每个 companyName 发送到服务器
  • 任务完成后关闭连接

看看这个Java代码：

服务器代码——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 ) ;
}
}
 

客户端代码——CrunchifyNIOClient.java

带有服务器-客户端示例的 Java NIO（非阻塞 I:O） - 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 ) ;
}
}

服务器端的结果：

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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 . . .

客户端结果：

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

几个常见问题解答：

  1. 从客户端，我如何维护持久连接？
    • 你可以使用socket.setKeepAlive(true); 从客户端建立连接。
  2. 如何阅读对发送到服务器的消息的响应。 服务器每 10 秒不断生成消息。 我只需要阅读对我的请求的回复。 据我了解，TCP“流”数据而不是记录结束等。
    • 对于客户端服务器通信，需要明确定义协议。 readLine()调用将被阻塞，直到所有数据都返回，所以不要使用它。 Try reading bytes from the stream until -1 is returned.

让我知道这是否有效。