前言
上文
【從入門到放棄-SpringBoot】SpringBoot源碼分析-請求過程中我們了解到，tomcat接收、傳回請求的過程都是基于NIO實作的。日常工作中有很多基于NIO的使用，我們知道NIO可以提高系統的并發度，接下來的系列我們來深入學習下NIO，本文先從使用上簡單概述。
NIO概述
NIO即non-blocking（New IO），是指jdk1.4 及以上版本裡提供的新api。
NIO和IO最大的差別：IO是以流的方式處理資料，而NIO是以塊的方式處理資料；IO對事件的處理是阻塞的，NIO是非阻塞的
NIO的核心部分：
- Channel
- Buffer
- Selector
NIO主要分為标準輸入輸出和網絡請求
标準輸入輸出NIO
讀取
private static void readNio() {
try {
//1、開啟檔案讀取流
FileInputStream fileInputStream = new FileInputStream("/Users/my/Desktop/123.txt");
//2、擷取fileChannel
FileChannel channel = fileInputStream.getChannel();
//3、設定ByteBuffer大小，一次能容納capacity位元組
int capacity = 9;
ByteBuffer bf = ByteBuffer.allocate(capacity);
//4、當read傳回-1時，表示檔案讀取完畢
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置為0，友善下次讀取
bf.clear();
}
channel.close();
fileInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
} 寫入
private static void writeNio() {
try {
//1、打開檔案寫入流
FileOutputStream fileOutputStream = new FileOutputStream("/Users/my/Desktop/123.txt");
//2、擷取fileChannel
FileChannel channel = fileOutputStream.getChannel();
//3、初始化byteBuffer
String str = "薩達案發生大大sdada34;sdds'";
ByteBuffer bf = ByteBuffer.allocate(1024);
//4、将bf position置為0，友善下次讀取
bf.clear();
//5、從byteBuffer的position位置填充byte
bf.put(str.getBytes());
//6、将bf position置為0，limit設定為position避免寫入内容過多
bf.flip();
int length = 0;
//7、如果position小于limit即未寫入完畢
while (bf.hasRemaining()) {
//8、将buffer内容寫入channel
length = channel.write(bf);
System.out.println(bf);
}
channel.close();
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
} 網絡NIO
服務端
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();
//綁定本機8001端口
server.socket().bind(new InetSocketAddress(8001));
//設定為非阻塞模式
server.configureBlocking(false);
//開啟selector管理器
selector = Selector.open();
//将selector注冊至server，并設定隻處理accept事件
server.register(selector, SelectionKey.OP_ACCEPT);
return this;
}
public void listen() throws Exception {
System.out.println("server start");
//無限循環持續監聽
while (true) {
//會阻塞 直到監聽到注冊的事件
selector.select();
//擷取喚醒的事件
Iterator<SelectionKey> selectorKeys = selector.selectedKeys().iterator();
while (selectorKeys.hasNext()) {
SelectionKey key = selectorKeys.next();
//将已取出的SelectionKey删除，防止重複處理
selectorKeys.remove();
if (key.isAcceptable()) {
//擷取到服務端的socket
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
//擷取接收到的用戶端socket
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
//向用戶端寫消息
socketChannel.write(ByteBuffer.wrap(new String("hello, this is server").getBytes()));
//注冊監聽read事件
socketChannel.register(selector, SelectionKey.OP_READ);
System.out.println("accept");
} else if (key.isReadable()) {
//使用selector擷取channel
SocketChannel socketChannel = (SocketChannel) key.channel();
socketChannel.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.allocate(1024);
//讀消息
int length = socketChannel.read(buffer);
String string = new String(buffer.array(), 0 , length);
System.out.println("read:" + socketChannel + string);
//寫消息
socketChannel.write(ByteBuffer.wrap(("server " + System.currentTimeMillis()).getBytes()));
Thread.sleep(10000);
}
}
}
}
}
用戶端
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);
}
}
}
}
}
總結
上述示例展示了最簡單的檔案NIO和網絡NIO用法，接下來會深入分析每個方法的源碼，并對性能進行調優。
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