前言
上文【从入门到放弃-SpringBoot】SpringBoot源码分析-请求过程中我们了解到，tomcat接收、返回请求的过程都是基于NIO实现的。日常工作中有很多基于NIO的使用，我们知道NIO可以提高系统的并发度，接下来的系列我们来深入学习下NIO，本文先从使用上简单概述。
NIO概述
NIO即non-blocking（New IO），是指jdk1.4 及以上版本里提供的新api。
NIO和IO最大的区别：IO是以流的方式处理数据，而NIO是以块的方式处理数据；IO对事件的处理是阻塞的，NIO是非阻塞的
NIO的核心部分：
- Channel
- Buffer
- Selector
NIO主要分为标准输入输出和网络请求
标准输入输出NIO
读取
private static void readNio() {
try {
//1、开启文件读取流
FileInputStream fileInputStream = new FileInputStream("/Users/my/Desktop/123.txt");
//2、获取fileChannel
FileChannel channel = fileInputStream.getChannel();
//3、设置ByteBuffer大小，一次能容纳capacity字节
int capacity = 9;
ByteBuffer bf = ByteBuffer.allocate(capacity);
//4、当read返回-1时，表示文件读取完毕
int length = -1;
while ((length = channel.read(bf)) != -1) {
byte[] bytes = bf.array();
System.out.println(new String(bytes, 0, length));
//4、将bf position置为0，方便下次读取
bf.clear();
}
channel.close();
fileInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}写入
private static void writeNio() {
try {
//1、打开文件写入流
FileOutputStream fileOutputStream = new FileOutputStream("/Users/my/Desktop/123.txt");
//2、获取fileChannel
FileChannel channel = fileOutputStream.getChannel();
//3、初始化byteBuffer
String str = "萨达案发生大大sdada34;sdds'";
ByteBuffer bf = ByteBuffer.allocate(1024);
//4、将bf position置为0，方便下次读取
bf.clear();
//5、从byteBuffer的position位置填充byte
bf.put(str.getBytes());
//6、将bf position置为0，limit设置为position避免写入内容过多
bf.flip();
int length = 0;
//7、如果position小于limit即未写入完毕
while (bf.hasRemaining()) {
//8、将buffer内容写入channel
length = channel.write(bf);
System.out.println(bf);
}
channel.close();
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}网络NIO
服务端
package com.my.tools.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.Iterator;
public class ServerSocket {
private static ServerSocket serverSocket;
private Selector selector;
public static void main(String[] args) throws Exception {
ServerSocket.getInstance().init(8001).listen();
}
public static ServerSocket getInstance() {
if (serverSocket == null) {
synchronized (ServerSocket.class) {
if (serverSocket == null) {
serverSocket = new ServerSocket();
}
}
}
return serverSocket;
}
public ServerSocket init(int port) throws IOException {
//初始化channel
ServerSocketChannel server = ServerSocketChannel.open();
//绑定本机8001端口
server.socket().bind(new InetSocketAddress(8001));
//设置为非阻塞模式
server.configureBlocking(false);
//开启selector管理器
selector = Selector.open();
//将selector注册至server，并设置只处理accept事件
server.register(selector, SelectionKey.OP_ACCEPT);
return this;
}
public void listen() throws Exception {
System.out.println("server start");
//无限循环持续监听
while (true) {
//会阻塞 直到监听到注册的事件
selector.select();
//获取唤醒的事件
Iterator<SelectionKey> selectorKeys = selector.selectedKeys().iterator();
while (selectorKeys.hasNext()) {
SelectionKey key = selectorKeys.next();
//将已取出的SelectionKey删除，防止重复处理
selectorKeys.remove();
if (key.isAcceptable()) {
//获取到服务端的socket
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
//获取接收到的客户端socket
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
//向客户端写消息
socketChannel.write(ByteBuffer.wrap(new String("hello, this is server").getBytes()));
//注册监听read事件
socketChannel.register(selector, SelectionKey.OP_READ);
System.out.println("accept");
} else if (key.isReadable()) {
//使用selector获取channel
SocketChannel socketChannel = (SocketChannel) key.channel();
socketChannel.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.allocate(1024);
//读消息
int length = socketChannel.read(buffer);
String string = new String(buffer.array(), 0 , length);
System.out.println("read:" + socketChannel + string);
//写消息
socketChannel.write(ByteBuffer.wrap(("server " + System.currentTimeMillis()).getBytes()));
Thread.sleep(10000);
}
}
}
}
}
客户端
package com.my.tools.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;
public class ClientSocket {
public static ClientSocket clientSocket;
private static Selector selector;
public static void main(String[] args) throws Exception {
ClientSocket.getInstance().init("localhost", 8001).listen();
}
public static ClientSocket getInstance() {
if (clientSocket == null) {
synchronized (ClientSocket.class) {
if (clientSocket == null) {
clientSocket = new ClientSocket();
}
}
}
return clientSocket;
}
public ClientSocket init(String ip, int port) throws IOException {
SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress(ip, port));
socketChannel.configureBlocking(false);
selector = Selector.open();
socketChannel.register(selector, SelectionKey.OP_CONNECT | SelectionKey.OP_READ);
return this;
}
public void listen() throws Exception {
System.out.println("client start");
while (true) {
selector.select();
Iterator<SelectionKey> selectionKeys = selector.selectedKeys().iterator();
while (selectionKeys.hasNext()) {
SelectionKey selectionKey = selectionKeys.next();
selectionKeys.remove();
if (selectionKey.isConnectable()) {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
socketChannel.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.wrap(new String("hello, this is client").getBytes());
socketChannel.write(buffer);
socketChannel.register(selector, SelectionKey.OP_READ);
System.out.println("client write");
} else if (selectionKey.isReadable()) {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
socketChannel.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.allocate(1024);
int length = socketChannel.read(buffer);
System.out.println("client read: " + socketChannel + new String(buffer.array(), 0, length));
socketChannel.write(ByteBuffer.wrap(("client " + System.currentTimeMillis()).getBytes()));
Thread.sleep(10000);
}
}
}
}
}
总结
上述示例展示了最简单的文件NIO和网络NIO用法，接下来会深入分析每个方法的源码，并对性能进行调优。