一、JAVA NIO
在介绍NIO编程之前，我们首先需要澄清一个概念：NIO到底是什么的简称?有人称之为New I/O，因为它相对于之前的I/O类库是新增的，所以被称为New I/O，这是它的官方叫法。但是，由于之前老的I/O类库是阻塞I/O，New I/O类库的目标就是要让Java支持非阻塞I/O，所以，更多的人喜欢称之为非阻塞I/O（Non-block I/O），由于非阻塞I/O更能够体现NIO的特点，所以本文使用的NIO都指的是非阻塞I/O。1.1 NIO类库简介
新的输入/输出（NIO）库是在JDK 1.4中引入的。NIO弥补了原来同步阻塞I/O的不足，它在标准Java代码中提供了高速的、面向块的I/O。通过定义包含数据的类，以及通过以块的形式处理这些数据，NIO不用使用本机代码就可以利用低级优化，这是原来的I/O包所无法做到的。下面我们对NIO的一些概念和功能做下简单介绍，以便大家能够快速地了解NIO类库和相关概念。1.1.1 缓冲区Buffer
我们首先介绍缓冲区（Buffer）的概念，Buffer是一个对象，它包含一些要写入或者要读出的数据。在NIO类库中加入Buffer对象，体现了新库与原I/O的一个重要区别。在面向流的I/O中，可以将数据直接写入或者将数据直接读到Stream对象中。 在NIO库中，所有数据都是用缓冲区处理的。在读取数据时，它是直接读到缓冲区中的；在写入数据时，写入到缓冲区中。任何时候访问NIO中的数据，都是通过缓冲区进行操作。 缓冲区实质上是一个数组。通常它是一个字节数组（ByteBuffer），也可以使用其他种类的数组。但是一个缓冲区不仅仅是一个数组，缓冲区提供了对数据的结构化访问以及维护读写位置（limit）等信息。 最常用的缓冲区是ByteBuffer，一个ByteBuffer提供了一组功能用于操作byte数组。除了ByteBuffer，还有其他的一些缓冲区，事实上，每一种Java基本类型（除了Boolean类型）都对应有一种缓冲区，具体如下：- ByteBuffer：字节缓冲区
- CharBuffer：字符缓冲区
- ShortBuffer：短整型缓冲区
- IntBuffer：整形缓冲区
- LongBuffer：长整形缓冲区
- FloatBuffer：浮点型缓冲区
- DoubleBuffer：双精度浮点型缓冲区
缓冲区的类图继承关系图：
每一个Buffer类都是Buffer接口的一个子实例。除了ByteBuffer，每一个 Buffer类都有完全一样的操作，只是它们所处理的数据类型不一样。因为大多数标准I/O操作都使用ByteBuffer，所以它除了具有一般缓冲区的操作之外还提供一些特有的操作，方便网络读写。
1.1.2.通道Channel
Channel是一个通道，可以通过它读取和写入数据，它就像自来水管一样，网络数据通过Channel读取和写入。通道与流的不同之处在于通道是双向的，流只是在一个方向上移动（一个流必须是InputStream或者OutputStream的子类），而且通道可以用于读、写或者同时用于读写。 因为Channel是全双工的，所以它可以比流更好地映射底层操作系统的API。特别是在UNIX网络编程模型中，底层操作系统的通道都是全双工的，同时支持读写操作。Channel的类图继承关系如图:
自顶向下看，前三层主要是Channel接口，用于定义它的功能，后面是一些具体的功能类（抽象类），从类图可以看出，实际上Channel可以分为两大类：分别是用于网络读写的SelectableChannel和用于文件操作的FileChannel。
本文涉及的ServerSocketChannel和SocketChannel都是SelectableChannel的子类，关于它们的具体用法将在后续的代码中体现。1.1.3.多路复用器Selector
Selector是Java NIO编程的基础，熟练地掌握Selector对于掌握NIO编程至关重要。多路复用器提供选择已经就绪的任务的能力。简单来讲，Selector会不断地轮询注册在其上的Channel，如果某个Channel上面有新的TCP连接接入、读和写事件，这个Channel就处于就绪状态，会被Selector轮询出来，然后通过SelectionKey可以获取就绪Channel的集合，进行后续的I/O操作。 一个多路复用器Selector可以同时轮询多个Channel，由于JDK使用了epoll()代替传统的select实现，所以它并没有最大连接句柄1024/2048的限制。这也就意味着只需要一个线程负责Selector的轮询，就可以接入成千上万的客户端，这确实是个非常巨大的进步。NIO服务端序列图：
NIO客户端时序图：
1.1.4 NIO代码示例
服务端代码 MultiplexerTimeServerpackage 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;
/**
* Created by user-hfc on 2017/10/29.
*/
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
*/
public MultiplexerTimeServer(int port) {
try {
selector = Selector.open(); //创建Selector
servChannel = ServerSocketChannel.open(); //打开ServerSocketChannel
servChannel.configureBlocking(false);
servChannel.socket().bind(new InetSocketAddress(port), 1024); //绑定监听地址
servChannel.register(selector, SelectionKey.OP_ACCEPT); //将打开ServerSocketChannel注册到 Selector
System.out.println("The time server is start in port : " + port);
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
public void stop() {
this.stop = true;
}
@Override
public void run() {
while (!stop) {
try {
selector.select(1000); //selector 轮训就绪的key
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectionKeys.iterator();
SelectionKey key = null;
while (it.hasNext()) {
key = it.next();
it.remove();
try {
handleInput(key); //处理输入
} catch (Exception e) {
if (null != key) {
key.cancel();
if (null != key.channel()) {
key.channel().close();
}
}
}
}
} catch (Exception e2) {
e2.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
// 所以不需要重复释放资源
if (null != selector) {
try {
selector.close();
} catch (Exception e3) {
e3.printStackTrace();
}
}
}
private void handleInput(SelectionKey key) throws IOException {
//处理新接入的请求信息
if (key.isAcceptable()) {
//Accept the new connection
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel sc = ssc.accept(); //接受请求
sc.configureBlocking(false);
//Add the new connection to the selector
sc.register(selector, SelectionKey.OP_READ); //接受请求之后注册监听读取请求
}
if (key.isReadable()) {
//Read the data
SocketChannel sc = (SocketChannel) key.channel();
//KB
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
/**
* 由于我们已经将SocketChannel设置为异步非阻塞模式，因此这里的read()是非阻塞的
* 使用返回值进行判断，有三种可能的结果
* 返回值大于0：读取到字节，对字节进行编解码
* 返回值等于0：没有读取到字节，属于正常场景，忽略
* 返回值等于-1：链路已经关闭，需要关闭SocketChannel，释放资源
*/
int readBytes = sc.read(readBuffer);
if (readBytes > 0) {
//把buffer的当前位置更改成buffer缓冲区的第一个位置
//用于后续对缓冲区的读取操作
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String body = new String(bytes, "utf-8");
System.out.println("The time server receive order : " + 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 (null != response && response.trim().length() > 0) {
byte[] bytes = response.getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
writeBuffer.put(bytes);
writeBuffer.flip();
channel.write(writeBuffer);
}
}
}
TimeServer
package NIOInduction.NIO.Server;
import java.io.IOException;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/25 0025.
*/
public class TimeServer {
public static void main(String[] args) throws IOException {
int port = 8080;
if (args != null && args.length > 0) {
try {
port = Integer.valueOf(args[0]);
} catch (NumberFormatException ex) {
}
}
MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);
new Thread(timeServer, "NIO-MultiplexerTimeServer-001").start();
}
}
客户端代码
TimeClientHandle
package NIOInduction.NIO.Client;
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;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/25 0025.
*/
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 == null ? "127.0.0.1" : host;
this.port = port;
try {
selector = Selector.open();
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
}
public void run() {
try {
doConnect();
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
while (!stop) {
try {
selector.select(1000);
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectionKeys.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 (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
// 多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动注册并关闭，所以不需要重新释放资源
if (selector != null) {
try {
selector.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void handleInput(SelectionKey key) throws IOException {
if (key.isValid()) {
// 判断是否连接成功
SocketChannel sc = (SocketChannel) key.channel();
if (key.isConnectable()) {
if (sc.finishConnect()) {
// Add the new connection to the selector
sc.register(selector, SelectionKey.OP_READ);
doWrite(sc);
} else System.exit(1); // 连接失败，退出进程
}
if (key.isReadable()) {
// read data
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("Now is : " + 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 {
// 如果连接成功，则注册到多路复用器上，发送请求,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 2 service succeed");
}
}
TimeClient
package NIOInduction.NIO.Client;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/25 0025.
*/
public class TimeClient {
public static void main(String[] agrs) {
int port = 8080;
String hostAddr = "127.0.0.1";
if (agrs != null && agrs.length == 1) {
try {
port = Integer.valueOf(agrs[0]);
} catch (NumberFormatException ex) {
}
} else if (agrs != null && agrs.length == 2) {
try {
hostAddr = agrs[0];
port = Integer.valueOf(agrs[1]);
} catch (NumberFormatException ex) {
}
}
for (int i = 1; i <= 1000; i++) {
TimeClientHandle tc = new TimeClientHandle(hostAddr, port);
Thread tt = new Thread(tc, "线程" + i);
try {
// tt.sleep(1000);
tt.start();
} catch (Exception e) {
}
}
}
}
二、JAVA AIO
NIO2.0引入了新的异步通道的概念，并提供了异步文件通道和异步套接字通道的实现。异步通道提供两种方式获取获取操作结果。- 通过java.util.concurrent.Future类来表示异步操作的结果；
- 在执行异步操作的时候传入一个java.nio.channels。
package NIOInduction.AIO.Server;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.Date;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/26 0026.
*/
public class ReadCompletionHandler implements CompletionHandler<Integer, ByteBuffer> {
private AsynchronousSocketChannel channel;
public ReadCompletionHandler(AsynchronousSocketChannel channel) {
this.channel = channel;
}
@Override
public void completed(Integer result, ByteBuffer attachment) {
attachment.flip();
byte[] body = new byte[attachment.remaining()];
attachment.get(body);
try {
String req = new String(body, "UTF-8");
System.out.println("the time server seceive order : " + req);
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(req) ? new Date(
System.currentTimeMillis()
).toString() : "BAD ORDER";
doWrite(currentTime);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
private void doWrite(String currentTime) {
if (currentTime != null && currentTime.trim().length() > 0) {
byte[] bytes = (currentTime).getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
writeBuffer.put(bytes);
writeBuffer.flip();
channel.write(writeBuffer, writeBuffer,
new CompletionHandler<Integer, ByteBuffer>() {
public void completed(Integer result, ByteBuffer attachment) {
// 如果没有发送完成，则继续发送
if (attachment.hasRemaining())
channel.write(attachment, attachment, this);
}
public void failed(Throwable exc, ByteBuffer attachment) {
try {
channel.close();
} catch (IOException e) {
}
}
});
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try {
this.channel.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
AcceptCompletionHandler
package NIOInduction.AIO.Server;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/26 0026.
*/
public class AcceptCompletionHandler implements CompletionHandler<AsynchronousSocketChannel, AsyneTimeServerHandler> {
@Override
public void completed(AsynchronousSocketChannel result, AsyneTimeServerHandler attachment) {
attachment.asynchronousServerSocketChannel.accept(attachment, this);
ByteBuffer buffer = ByteBuffer.allocate(1024);
result.read(buffer, buffer, new ReadCompletionHandler(result));
}
@Override
public void failed(Throwable exc, AsyneTimeServerHandler attachment) {
exc.printStackTrace();
attachment.latch.countDown();
}
}
AsyneTimeServerHandler
package NIOInduction.AIO.Server;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.util.concurrent.CountDownLatch;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/26 0026.
*/
public class AsyneTimeServerHandler implements Runnable {
private int port;
CountDownLatch latch;/* 一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。*/
AsynchronousServerSocketChannel asynchronousServerSocketChannel;
public AsyneTimeServerHandler(int port) {
this.port = port;
try {
asynchronousServerSocketChannel = AsynchronousServerSocketChannel.open();
asynchronousServerSocketChannel.bind(new InetSocketAddress(port));
System.out.println("The Server start in port : " + port);
} catch (IOException e) {
e.printStackTrace();
}
}
public void run() {
latch = new CountDownLatch(1);
doAccept();
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void doAccept() {
asynchronousServerSocketChannel.accept(this, new AcceptCompletionHandler());
}
}
TimeServer
package NIOInduction.AIO.Server;
import java.io.IOException;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/26 0026.
*/
public class TimeServer {
public static void main(String[] args) throws IOException {
int port = 8080;
if (args != null && args.length > 0) {
try {
port = Integer.valueOf(args[0]);
} catch (NumberFormatException ex) {
}
}
AsyneTimeServerHandler timeServer = new AsyneTimeServerHandler(port);
new Thread(timeServer, "xxxx").start();
}
}
客户端代码 AsyncTimeClientHandler
package NIOInduction.AIO.Client;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.concurrent.CountDownLatch;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/26 0026.
*/
public class AsyncTimeClientHandler implements
CompletionHandler<Void, AsyncTimeClientHandler>, Runnable {
private AsynchronousSocketChannel client;
private String host;
private int port;
private CountDownLatch latch;
public AsyncTimeClientHandler(String host, int port) {
this.host = host;
this.port = port;
try {
client = AsynchronousSocketChannel.open();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void run() {
latch = new CountDownLatch(1);
client.connect(new InetSocketAddress(host, port), this, this);
try {
latch.await();
} catch (InterruptedException e1) {
e1.printStackTrace();
}
try {
client.close();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void completed(Void result, AsyncTimeClientHandler attachment) {
byte[] req = "QUERY TIME ORDER".getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
writeBuffer.put(req);
writeBuffer.flip();
client.write(writeBuffer, writeBuffer,
new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result, ByteBuffer buffer) {
if (buffer.hasRemaining()) {
client.write(buffer, buffer, this);
} else {
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
client.read(
readBuffer,
readBuffer,
new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result,
ByteBuffer buffer) {
buffer.flip();
byte[] bytes = new byte[buffer
.remaining()];
buffer.get(bytes);
String body;
try {
body = new String(bytes,
"UTF-8");
System.out.println("Now is : "
+ body);
latch.countDown();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
@Override
public void failed(Throwable exc,
ByteBuffer attachment) {
try {
client.close();
latch.countDown();
} catch (IOException e) {
// ingnore on close
}
}
});
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try {
client.close();
latch.countDown();
} catch (IOException e) {
// ingnore on close
}
}
});
}
@Override
public void failed(Throwable exc, AsyncTimeClientHandler attachment) {
exc.printStackTrace();
try {
client.close();
latch.countDown();
} catch (IOException e) {
e.printStackTrace();
}
}
}
TimeClient
package NIOInduction.AIO.Client;
/**
* Created by IntelliJ IDEA 14.
* User: karl.zhao
* Time: 2015/11/26 0026.
*/
public class TimeClient {
public static void main(String[] args) {
int port = 8080;
if (args != null && args.length > 0) {
try {
port = Integer.valueOf(args[0]);
} catch (NumberFormatException e) {
// 采用默认值
}
}
for (int i = 1; i <= 20; i++) {
AsyncTimeClientHandler tc = new AsyncTimeClientHandler("127.0.0.1", port);
Thread tt = new Thread(tc, "线程" + i);
try {
// tt.sleep(1000);
tt.start();
} catch (Exception e) {
}
}
}
}
三、4种I/O对比
3.1 概念澄清
1.异步非阻塞IO
很多人喜欢将JDK1.4提供的NIO框架称为异步非阻塞I/O，但是，如果严格按照UNIX网络编程模型和JDK的实现进行区分，实际上它只能被称为非阻塞I/O，不能叫异步非阻塞I/O。在早期的JDK1.4和1.5 update10版本之前，JDK的Selector基于select/poll模型实现，它是基于I/O复用技术的非阻塞I/O，不是异步I/O。在JDK1.5 update10和Linux core2.6以上版本，Sun优化了Selctor的实现，它在底层使用epoll替换了select/poll，上层的API并没有变化，可以认为是JDK NIO的一次性能优化，但是它仍旧没有改变I/O的模型。 由JDK1.7提供的NIO2.0，新增了异步的套接字通道，它是真正的异步I/O，在异步I/O操作的时候可以传递信号变量，当操作完成之后会回调相关的方法，异步I/O也被称为AIO。2.多路复用器Selector
在前面的章节我们介绍过Java NIO的实现关键是多路复用I/O技术，多路复用的核心就是通过Selector来轮询注册在其上的Channel，当发现某个或者多个Channel处于就绪状态后，从阻塞状态返回就绪的Channel的选择键集合，进行I/O操作。由于多路复用器是NIO实现非阻塞I/O的关键，它又是主要通过Selector实现的，所以本文将Selector翻译为多路复用器，与其他技术书籍所说的选择器是同一个东西。3.伪异步IO
伪异步I/O的概念完全来源于实践。在JDK NIO编程没有流行之前，为了解决Tomcat通信线程同步I/O导致业务线程被挂住的问题，大家想到了一个办法：在通信线程和业务线程之间做个缓冲区，这个缓冲区用于隔离I/O线程和业务线程间的直接访问，这样业务线程就不会被I/O线程阻塞。而对于后端的业务侧来说，将消息或者Task放到线程池后就返回了，它不再直接访问I/O线程或者进行I/O读写，这样也就不会被同步阻塞。类似的设计还包括前端启动一组线程，将接收的客户端封装成Task，放到后端的线程池执行，用于解决一连接一线程问题。像这样通过线程池做缓冲区的做法，本书中习惯于称它为伪异步I/O，而官方并没有伪异步I/O这种说法，请大家注意。3.2 不同IO模型对比
标签：java,NIO,port,IO,import,JAVA,ByteBuffer,public From： https://www.cnblogs.com/MuXinu/p/18091388