netty系列之Java BIO NIO AIO進(jìn)化史

簡(jiǎn)介

上一章我們介紹了IO的五種模型，實(shí)際上Java只支持其中的三種，即BIO/NIO/AIO。

本文將介紹Java中這三種IO的進(jìn)化史，并從使用的角度剖析它們背后的故事。

Java BIO

BIO概念解析

BIO，Blocking IO，阻塞IO，它是Java的上古產(chǎn)品，自出生就有的東西（JDK 1.0）。

使用BIO則數(shù)據(jù)準(zhǔn)備和數(shù)據(jù)從內(nèi)核空間拷貝到用戶(hù)空間兩個(gè)階段都是阻塞的。

BIO使用案例

public?class?EchoServer?{????public?static?void?main(String[]?args)?throws?IOException?{
????????ServerSocket?serverSocket?=?new?ServerSocket(8080);????????while?(true)?{
????????????System.out.println("start?accept");
????????????Socket?socket?=?serverSocket.accept();
????????????System.out.println("new?conn:?"?+?socket.getRemoteSocketAddress());????????????new?Thread(()->{????????????????try?{
????????????????????BufferedReader?reader?=?new?BufferedReader(new?InputStreamReader(socket.getInputStream()));
????????????????????String?msg;????????????????????//?讀取消息，本文來(lái)源公從號(hào)彤哥讀源碼
????????????????????while?((msg?=?reader.readLine())?!=?null)?{????????????????????????if?(msg.equalsIgnoreCase("quit"))?{
????????????????????????????reader.close();
????????????????????????????socket.close();????????????????????????????break;
????????????????????????}?else?{
????????????????????????????System.out.println("receive?msg:?"?+?msg);
????????????????????????}
????????????????????}
????????????????}?catch?(IOException?e)?{
????????????????????e.printStackTrace();
????????????????}
????????????}).start();
????????}
????}
}

客戶(hù)端可以使用telnet來(lái)測(cè)試，而且你可以使用多個(gè)telnet來(lái)測(cè)試：

[c:\~]$?telnet?127.0.0.1?8080Connecting?to?127.0.0.1:8080...
Connection?established.
To?escape?to?local?shell,?press?'Ctrl+Alt+]'.
hello?world
我是人才
quit
Connection?closed?by?foreign?host.

BIO的使用方式非常簡(jiǎn)單，服務(wù)端接收到一個(gè)連接就啟動(dòng)一個(gè)線程來(lái)處理這個(gè)連接的所有請(qǐng)求。

所以，BIO最大的缺點(diǎn)就是浪費(fèi)資源，只能處理少量的連接，線程數(shù)隨著連接數(shù)線性增加，連接越多線程越多，直到抗不住。

Java NIO

NIO概念解析

NIO，New IO，JDK1.4開(kāi)始支持，內(nèi)部是基于多路復(fù)用的IO模型。

這里有個(gè)歧義，很多人認(rèn)為Java的NIO是Non-Blocking IO的縮寫(xiě)，其實(shí)并不是。

使用NIO則多條連接的數(shù)據(jù)準(zhǔn)備階段會(huì)阻塞在select上，數(shù)據(jù)從內(nèi)核空間拷貝到用戶(hù)空間依然是阻塞的。

因?yàn)榈谝浑A段并不是連接本身處于阻塞階段，所以通常來(lái)說(shuō)NIO也可以看作是同步非阻塞IO。

NIO使用案例

public?class?EchoServer?{????public?static?void?main(String[]?args)?throws?IOException?{
????????Selector?selector?=?Selector.open();
????????ServerSocketChannel?serverSocketChannel?=?ServerSocketChannel.open();
????????serverSocketChannel.bind(new?InetSocketAddress(8080));
????????serverSocketChannel.configureBlocking(false);????????//?將accept事件綁定到selector上
????????serverSocketChannel.register(selector,?SelectionKey.OP_ACCEPT);????????while?(true)?{????????????//?阻塞在select上
????????????selector.select();
????????????Set<SelectionKey>?selectionKeys?=?selector.selectedKeys();????????????//?遍歷selectKeys
????????????Iterator<SelectionKey>?iterator?=?selectionKeys.iterator();????????????while?(iterator.hasNext())?{
????????????????SelectionKey?selectionKey?=?iterator.next();????????????????//?如果是accept事件
????????????????if?(selectionKey.isAcceptable())?{
????????????????????ServerSocketChannel?ssc?=?(ServerSocketChannel)?selectionKey.channel();
????????????????????SocketChannel?socketChannel?=?ssc.accept();
????????????????????System.out.println("accept?new?conn:?"?+?socketChannel.getRemoteAddress());
????????????????????socketChannel.configureBlocking(false);
????????????????????socketChannel.register(selector,?SelectionKey.OP_READ);
????????????????}?else?if?(selectionKey.isReadable())?{????????????????????//?如果是讀取事件，本文來(lái)源公從號(hào)彤哥讀源碼
????????????????????SocketChannel?socketChannel?=?(SocketChannel)?selectionKey.channel();
????????????????????ByteBuffer?buffer?=?ByteBuffer.allocate(1024);????????????????????//?將數(shù)據(jù)讀入到buffer中
????????????????????int?length?=?socketChannel.read(buffer);????????????????????if?(length?>?0)?{
????????????????????????buffer.flip();????????????????????????byte[]?bytes?=?new?byte[buffer.remaining()];????????????????????????//?將數(shù)據(jù)讀入到byte數(shù)組中
????????????????????????buffer.get(bytes);????????????????????????//?換行符會(huì)跟著消息一起傳過(guò)來(lái)
????????????????????????String?content?=?new?String(bytes,?"UTF-8").replace("\r\n",?"");????????????????????????if?(content.equalsIgnoreCase("quit"))?{
????????????????????????????selectionKey.cancel();
????????????????????????????socketChannel.close();
????????????????????????}?else?{
????????????????????????????System.out.println("receive?msg:?"?+?content);
????????????????????????}
????????????????????}
????????????????}
????????????????iterator.remove();
????????????}
????????}
????}
}

這里同樣使用telnet測(cè)試，而且你可以使用多個(gè)telnet來(lái)測(cè)試：

[c:\~]$?telnet?127.0.0.1?8080Connecting?to?127.0.0.1:8080...
Connection?established.
To?escape?to?local?shell,?press?'Ctrl+Alt+]'.
hello?world
我是人才
quit
Connection?closed?by?foreign?host.

NIO的使用方式就有點(diǎn)復(fù)雜了，但是一個(gè)線程就可以處理很多連接。

首先，需要注冊(cè)一個(gè)ServerSocketChannel并把它注冊(cè)到selector上并監(jiān)聽(tīng)accept事件，然后accept到連接后會(huì)獲取到SocketChannel，同樣把SocketChannel也注冊(cè)到selector上，但是監(jiān)聽(tīng)的是read事件。焦作國(guó)醫(yī)胃腸醫(yī)院靠譜嗎_正規(guī)胃腸專(zhuān)科醫(yī)院：http://jz.lieju.com/zhuankeyiyuan/37570896.htm

NIO最大的優(yōu)點(diǎn)，就是一個(gè)線程就可以處理大量的連接，缺點(diǎn)是不適合處理阻塞性任務(wù)，因?yàn)樽枞匀蝿?wù)會(huì)把這個(gè)線程占有著，其它連接的請(qǐng)求將得不到及時(shí)處理。

Java AIO

AIO概念介紹

AIO，Asynchronous IO，異步IO，JDK1.7開(kāi)始支持，算是一種比較完美的IO，Windows下比較成熟，但Linux下還不太成熟。

使用異步IO則會(huì)在請(qǐng)求時(shí)立即返回，并在數(shù)據(jù)已準(zhǔn)備且已拷貝到用戶(hù)空間后進(jìn)行回調(diào)處理，兩個(gè)階段都不會(huì)阻塞。

AIO使用案例

public?class?EchoServer?{????public?static?void?main(String[]?args)?throws?IOException?{
????????AsynchronousServerSocketChannel?serverSocketChannel?=?AsynchronousServerSocketChannel.open();
????????serverSocketChannel.bind(new?InetSocketAddress(8080));????????//?監(jiān)聽(tīng)accept事件，本文來(lái)源公從號(hào)彤哥讀源碼
????????serverSocketChannel.accept(null,?new?CompletionHandler<AsynchronousSocketChannel,?Object>()?{????????????@Override
????????????public?void?completed(AsynchronousSocketChannel?socketChannel,?Object?attachment)?{????????????????try?{
????????????????????System.out.println("accept?new?conn:?"?+?socketChannel.getRemoteAddress());????????????????????//?再次監(jiān)聽(tīng)accept事件
????????????????????serverSocketChannel.accept(null,?this);????????????????????//?消息的處理
????????????????????while?(true)?{
????????????????????????ByteBuffer?buffer?=?ByteBuffer.allocate(1024);????????????????????????//?將數(shù)據(jù)讀入到buffer中
????????????????????????Future<Integer>?future?=?socketChannel.read(buffer);????????????????????????if?(future.get()?>?0)?{
????????????????????????????buffer.flip();????????????????????????????byte[]?bytes?=?new?byte[buffer.remaining()];????????????????????????????//?將數(shù)據(jù)讀入到byte數(shù)組中
????????????????????????????buffer.get(bytes);

????????????????????????????String?content?=?new?String(bytes,?"UTF-8");????????????????????????????//?換行符會(huì)當(dāng)成另一條消息傳過(guò)來(lái)
????????????????????????????if?(content.equals("\r\n"))?{????????????????????????????????continue;
????????????????????????????}????????????????????????????if?(content.equalsIgnoreCase("quit"))?{
????????????????????????????????socketChannel.close();????????????????????????????????break;
????????????????????????????}?else?{
????????????????????????????????System.out.println("receive?msg:?"?+?content);
????????????????????????????}
????????????????????????}
????????????????????}
????????????????}?catch?(Exception?e)?{
????????????????????e.printStackTrace();
????????????????}
????????????}????????????@Override
????????????public?void?failed(Throwable?exc,?Object?attachment)?{
????????????????System.out.println("failed");
????????????}
????????});????????//?阻塞住主線程
????????System.in.read();
????}
}

這里同樣使用telnet測(cè)試，而且你可以使用多個(gè)telnet來(lái)測(cè)試：

[c:\~]$?telnet?127.0.0.1?8080Connecting?to?127.0.0.1:8080...
Connection?established.
To?escape?to?local?shell,?press?'Ctrl+Alt+]'.
hello?world
我是人才
quit
Connection?closed?by?foreign?host.

AIO的使用方式不算太復(fù)雜，默認(rèn)會(huì)啟一組線程來(lái)處理用戶(hù)的請(qǐng)求，而且如果在處理阻塞性任務(wù)，還會(huì)自動(dòng)增加新的線程來(lái)處理其它連接的任務(wù)。

首先，創(chuàng)建一個(gè)AsynchronousServerSocketChannel并調(diào)用其accept方法，這一步相當(dāng)于監(jiān)聽(tīng)了accept事件，在收到accept事件后會(huì)獲取到AsynchronousSocketChannel，然后就可以在回調(diào)方法completed()里面讀取數(shù)據(jù)了，當(dāng)然也要繼續(xù)監(jiān)聽(tīng)accept事件。

AIO最大的優(yōu)點(diǎn)，就是少量的線程就可以處理大量的連接，而且可以處理阻塞性任務(wù)，但不能大量阻塞，否則線程數(shù)量會(huì)膨脹。

槽點(diǎn)

（1）三種IO的實(shí)現(xiàn)方式中對(duì)于換行符的處理竟然都不一樣，BIO中不會(huì)把換行符帶過(guò)來(lái)（其實(shí)是帶過(guò)來(lái)了，因?yàn)橛昧藃eadLine()方法，所以換行符沒(méi)了），NIO中會(huì)把換行符加在消息末尾，AIO中會(huì)把換行符當(dāng)成一條新的消息傳過(guò)來(lái)，很神奇，為啥不統(tǒng)一處理呢，也很疑惑。焦作國(guó)醫(yī)胃腸醫(yī)院地址__大愛(ài)國(guó)醫(yī)：http://jz.lieju.com/zhuankeyiyuan/37570264.htm

（2）JDK自帶的ByteBuffer是一個(gè)難用的東西。

總結(jié)

本文我們從概念和使用兩個(gè)角度分別介紹了BIO/NIO/AIO三種IO模型。

問(wèn)題

看起來(lái)JDK的實(shí)現(xiàn)似乎很完美啊，為什么還會(huì)有Netty呢？

最后，也歡迎來(lái)我的公從號(hào)彤哥讀源碼系統(tǒng)地學(xué)習(xí)源碼&架構(gòu)的知識(shí)。