NIO多路复用器 - Seletor
# 多路复用器
## select
1、select选择器会告诉客户端哪些连接有数据要读取，但是读取的操作还是用户自己触发的，这种叫做「同步」
```java
package com.ibli.javaBase.nio;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;
/**
* @Author gaolei
* @Date 2021/4/3 4:09 下午
* @Version 1.0
*/
public class SelectMultiple {
private ServerSocketChannel server = null;
private Selector selector = null;
int port = 9090;
public void initServer() throws IOException {
server = ServerSocketChannel.open();
server.configureBlocking(false);
server.bind(new InetSocketAddress(port));
server.register(selector, SelectionKey.OP_ACCEPT);
}
public void start() throws IOException {
initServer();
System.err.println("server started ....");
while (true) {
// selector.select() 调用系统内核的select
while (selector.select() > 0) {
// 从多路复用器中选择有效的key
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> iter = selectionKeys.iterator();
while (iter.hasNext()) {
SelectionKey key = iter.next();
if (key.isAcceptable()) {
acceptHandle(key);
} else if (key.isReadable()) {
readHandle(key);
}
}
}
}
}
public void acceptHandle(SelectionKey key) throws IOException {
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel client = ssc.accept();
client.configureBlocking(false);
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(1024);
client.register(selector, SelectionKey.OP_READ, byteBuffer);
System.err.println("client arrived " + client.getRemoteAddress());
}
public void readHandle(SelectionKey key) throws IOException {
SocketChannel client = (SocketChannel) key.channel();
ByteBuffer buffer = (ByteBuffer) key.attachment();
buffer.clear();
int read = 0;
while (true) {
read = client.read(buffer);
if (read > 0) {
// 服务端读到的数据，再写一遍给到客户端
buffer.flip();
while (buffer.hasRemaining()) {
client.write(buffer);
}
buffer.clear();
} else if (read == 0) {
break;
} else {
// client 发生错误 或者断开 read == -1
// 导致空转 最终CPU达到100%
client.close();
break;
}
}
}
}
```
>i 上面的写法是一个selector既担任boss又担任worker