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非阻塞式IO通信

一、简介

非阻塞IO(NIO)弥补了原来同步阻塞IO的不足,NIO有三个重要概念:
  • 缓冲区Buffer:缓冲待读写处理的数据,NIO是读写数据操作的就是Buffer;
  • 通道Channel:数据通过的双向通道;
  • 多路复用器Selector:负责多路复用;

二、NIO服务端&客户端流程

下面是NIO服务端的时序图:
  1. 1.
    打开ServerSocketChannel,用于监听客户端的连接,它是所有客户端连接的父管道(对应BIO的ServerSocket);
  2. 2.
    绑定监听端口,设置连接方式为非阻塞模式;
  3. 3.
    创建Reactor线程,创建多路复用器Selector并启动线程;
  4. 4.
    将ServerSocketChannel注册到Reactor线程的多路复用器Selector上,监听ACCEPT事件;
  5. 5.
    多路复用器在线程run方法的无限循环体内轮询准备就绪的Key;
  6. 6.
    多路复用器监听到有新的客户端接入,处理新的接入请求,完成TCP三次握手,建立物理链路;
  7. 7.
    设置客户端链路为非阻塞模型;
  8. 8.
    将新接入的客户端连接注册到Reactor线程的多路复用器上,监听读操作,读取客户端发送的网络消息;
  9. 9.
    异步读取客户端消息到缓冲区;
  10. 10.
    对ByteBuffer进行编解码,如果有半包消息指针reset,继续读取后续的报文,将解码成功的消息封装成Task,投递到业务线程池中,进行业务逻辑编排;
  11. 11.
    将POJO对象encode成ByteBuffer,调用SocketChannel的异步write接口,将消息异步发送给客户端。
注意:如果发送区TCP缓冲区满,会导致写半包,此时,需要注册监听写操作位,循环写,直到整包消息写入TCP缓冲区。
下面是NIO客户端的时序图:
  1. 1.
    打开SocketChannel,绑定客户端本地地址(可选,默认系统会随机分配一个可用的本地地址);
  2. 2.
    设置SocketChannel为非阻塞模式,同时设置客户端连接的TCP参数;
  3. 3.
    异步连接服务端;
  4. 4.
    判断是否连接成功,如果连接成功则直接注册读状态位到多路复用器中(步骤10),如果当前没有连接成功(异步连接,返回false,说明客户端已经发送sync包,服务端没有返回ack包,物理链路还没有建立),向多路复用器注册连接状态位(步骤5);
  5. 5.
    向Reactor线程的多路复用器注册OP_CONNECT状态位,监听服务端的TCP ACK应答;
  6. 6.
    创建Reactor线程,创建多路复用器并启动线程;
  7. 7.
    多路复用器在线程run方法的无限循环体内轮询准备就绪的key;
  8. 8.
    接收connect事件并进行处理;
  9. 9.
    判断连接是否完成,如果完成执行步骤10;
  10. 10.
    注册读事件到多路复用器;
  11. 11.
    异步读客户端请求到缓冲区;
  12. 12.
    对ByteBuffer进行编解码,如果有半包消息接收缓冲区Reset,继续读取后续的报文,将解码成功的消息封装成Task,投递到业务线程池中,进行业务逻辑编排。
  13. 13.
    将POJO对象encode成ByteBuffer,调用SocketChannel的异步write接口,将消息异步发送给客户端。

三、代码实例

3.1 服务端

TimeServer.java
package com.wangjun.io.nio;
/**
* @author wangjun
* @date 2020-03-30
* @version 1.0
*/
public class TimeServer {
public static void main(String[] args) {
int port = 8080;
MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);
new Thread(timeServer, "NIO_MultiplexerTimeServer-001").start();
}
}
MultiplexerTimeServer.java
package com.wangjun.io.nio;
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.Date;
import java.util.Iterator;
import java.util.Set;
/**
* @author wangjun
* @date 2020-03-30
* @version 1.0
*/
public class MultiplexerTimeServer implements Runnable {
private Selector selector;
private ServerSocketChannel servChannel;
private volatile boolean stop;
/**
* 初始化多路复用器,绑定监听端口
*
* @param port
*/
public MultiplexerTimeServer(int port) {
try {
selector = Selector.open();
servChannel = ServerSocketChannel.open();
servChannel.configureBlocking(false);
servChannel.socket().bind(new InetSocketAddress(port), 1024);//???1024这个参数什么作用
servChannel.register(selector, SelectionKey.OP_ACCEPT);
System.out.println("The nio time server start in port:" + port);
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
}
public void stop() {
this.stop = true;
}
@Override
public void run() {
while (!stop) {
try {
//休眠时间为1秒,无论是否有读写事件,selector每个1s被唤醒一次
selector.select(1000);
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
SelectionKey key = null;
while (it.hasNext()) {
key = it.next();
it.remove();
try {
handleInput(key);
} catch (Exception e) {
if (key != null) {
key.cancel();
if (key.channel() != null) {
key.channel().close();
}
}
}
}
} catch (Throwable t) {
t.printStackTrace();
}
}
//多路复用器关闭后,所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭,所有不需要重复释放资源
if (selector != null) {
try {
selector.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void handleInput(SelectionKey key) throws IOException {
if (key.isValid()) {
// 处理新接入的请求消息
if (key.isAcceptable()) {
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
}
if (key.isReadable()) {
SocketChannel sc = (SocketChannel) key.channel();
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
int readBytes = sc.read(readBuffer);
if (readBytes > 0) {
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String body = new String(bytes, "UTF-8");
System.out.println("时间服务器收到的命令是:" + body);
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)
? new Date(System.currentTimeMillis()).toString()
: "BAD ORDER";
doWrite(sc, currentTime);
} else if (readBytes < 0) {
// 对端链路关闭
key.cancel();
sc.close();
} else {
// 读到0字节,忽略
}
}
}
}
private void doWrite(SocketChannel channel, String response) throws IOException {
if(response != null && response.trim().length() > 0) {
byte[] bytes = response.getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
writeBuffer.put(bytes);
writeBuffer.flip();
channel.write(writeBuffer);
}
}
}

3.2 客户端

TimeClient.java
package com.wangjun.io.nio;
/**
* @author wangjun
* @date 2020-03-30
* @version 1.0
*/
public class TimeClient {
public static void main(String[] args) {
int port = 8080;
new Thread(new TimeClientHandle("127.0.0.1", port), "TimeClient-001").start();
}
}
TimeClientHandle.java
package com.wangjun.io.nio;
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.SocketChannel;
import java.util.Iterator;
import java.util.Set;
/**
* @author wangjun
* @date 2020-03-30
* @version 1.0
*/
public class TimeClientHandle implements Runnable {
private String host;
private int port;
private Selector selector;
private SocketChannel socketChannel;
private volatile boolean stop;
public TimeClientHandle(String host, int port) {
this.host = host;
this.port = port;
try {
selector = Selector.open();
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
}
@Override
public void run() {
try {
doConnect();
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
while(!stop) {
try {
selector.select(1000);
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
SelectionKey key = null;
while (it.hasNext()) {
key = it.next();
it.remove();
try {
handleInput(key);
} catch (Exception e) {
if (key != null) {
key.cancel();
if (key.channel() != null) {
key.channel().close();
}
}
}
}
} catch (Throwable t) {
t.printStackTrace();
}
}
//多路复用器关闭后,所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭,所有不需要重复释放资源
if (selector != null) {
try {
selector.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void handleInput(SelectionKey key) throws IOException {
if (key.isValid()) {
// 判断连接是否成功
SocketChannel sc = (SocketChannel) key.channel();
if(key.isConnectable()) {
if(sc.finishConnect()) {
sc.register(selector, SelectionKey.OP_READ);
doWrite(sc);
}else {
System.exit(1);
}
}
if (key.isReadable()) {
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
int readBytes = sc.read(readBuffer);
if (readBytes > 0) {
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String body = new String(bytes, "UTF-8");
System.out.println("现在的时间是:" + body);
this.stop = true;
} else if (readBytes < 0) {
// 对端链路关闭
key.cancel();
sc.close();
} else {
// 读到0字节,忽略
}
}
}
}
private void doConnect() throws IOException {
//如果直连成功,则注册到多路复用器上,发送请求消息,读应答
if(socketChannel.connect(new InetSocketAddress(host, port))) {
socketChannel.register(selector, SelectionKey.OP_READ);
doWrite(socketChannel);
}else {
socketChannel.register(selector, SelectionKey.OP_CONNECT);
}
}
private void doWrite(SocketChannel sc) throws IOException {
byte[] req = "QUERY TIME ORDER".getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
writeBuffer.put(req);
writeBuffer.flip();
sc.write(writeBuffer);
if(!writeBuffer.hasRemaining()) {
System.out.println("send order to server succeed!");
}
}
}

3.3 运行服务端和客户端

服务端运行结果:
The nio time server start in port:8080
时间服务器收到的命令是:QUERY TIME ORDER
客户端运行结果:
send order to server succeed!
现在的时间是:Tue Mar 31 10:13:47 CST 2020

四、NIO的好处

  1. 1.
    客户端发起的链接操作是异步的,可以通过多路复用器注册OP_CONNECT等待后续结果,不需要像之前的客户端那样被同步阻塞;
  2. 2.
    SocketChannel的读写操作都是异步的,如果没有可读写的数据它不会同步等待,直接返回,这样IO通信线程就可以处理其他的链路,不需要同步等待这个链路可用;
  3. 3.
    线程模型的优化:由于JDK的Selector在Linux等主流操作系统上通过epoll实现,它没有连接句柄数的限制(只受限于操作系统的最大句柄数或者单个进程的句柄数限制),这意味着一个Selector线程可以同时处理成千上万个客户端连接,而且性能不会随着客户端的增加而性能下降。因此,它非常适合做高性能、高负载的网络服务器。
参考:
《Netty权威指南》
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On this page
一、简介
二、NIO服务端&客户端流程
三、代码实例
3.1 服务端
3.2 客户端
3.3 运行服务端和客户端
四、NIO的好处