前面兩篇文章介紹了NIO中的Buffer和Channel,有了以前的基礎,這篇文章來介紹一下另外一個比較重要的概念----Selector。咱們知道系統線程的切換是消耗系統資源的,若是咱們每個鏈接都用一個線程來管理,資源的開銷會很是大,這個時候就能夠用Selector。經過Selector能夠實現一個線程管理多個Channel,以下圖:java
使用以前得到一個Selector對象bash
Selector selector = Selector.open();
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要把Channel註冊到Selector上,Channel必需是非阻塞的。所以FileChannel是沒法註冊到Selector的。若是註冊的時候不調用configureBlocking
方法就會拋出IllegalBlockingModeException
異常。微信
SelectionKey共有四種socket
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
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ServerSocketChannel的Operation Set只能是OP_ACCEPT,若是在註冊的時候添加了OP_CONNECT、OP_WRITE或OP_READ會報異常。例如按照如下寫法ui
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT | SelectionKey.OP_CONNECT);
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就會拋出下面的異常spa
Exception in thread "main" java.lang.IllegalArgumentException
at java.nio.channels.spi.AbstractSelectableChannel.register(AbstractSelectableChannel.java:199)
at java.nio.channels.SelectableChannel.register(SelectableChannel.java:280)
at com.nio.sample.selector.SelectorServerSocketChannelSample.main(SelectorServerSocketChannelSample.java:27)
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ServerSocketChannel的validOps
能夠看到只有OP_ACCEPT是合法的線程
public final int validOps() {
return SelectionKey.OP_ACCEPT;
}
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socketChannel.register(selector, SelectionKey.OP_CONNECT);
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SocketChannel的Operation Set只能是OP_CONNECT、OP_WRITE和OP_READ,若是在註冊的時候添加了OP_ACCEPT一樣會報異常。3d
SocketChannel的validOps
能夠看到只有OP_READ、OP_WRITE、OP_CONNECT是合法的rest
public final int validOps() {
return (SelectionKey.OP_READ
| SelectionKey.OP_WRITE
| SelectionKey.OP_CONNECT);
}
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註冊成功以後,咱們經過一個demo實現,客戶端和服務端交互:code
服務端:
public static void main(String[] args) throws Exception {
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.socket().bind(new InetSocketAddress(9000));
serverSocketChannel.configureBlocking(false);
Selector selector = Selector.open();
// configureBlocking 若是不設置非阻塞,register的時候會報異常
// java.nio.channels.IllegalBlockingModeException
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
int selected = selector.select();
if (selected > 0) {
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while (iterator.hasNext()) {
SelectionKey selectionKey = iterator.next();
iterator.remove();
if (selectionKey.isAcceptable()) {
System.err.println("Acceptable");
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
socketChannel.register(selector, SelectionKey.OP_READ);
} else if (selectionKey.isReadable()) {
System.err.println("Readable");
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
ByteBuffer buffer = ByteBuffer.allocate(128);
socketChannel.read(buffer);
System.out.println("接收來自客戶端的數據:" + new String(buffer.array()));
selectionKey.interestOps(SelectionKey.OP_WRITE);
} else if (selectionKey.isWritable()) {
System.err.println("Writable");
SocketChannel channel = (SocketChannel) selectionKey.channel();
String content = "向客戶端發送數據 : " + System.currentTimeMillis();
ByteBuffer buffer = ByteBuffer.wrap(content.getBytes());
channel.write(buffer);
selectionKey.interestOps(SelectionKey.OP_READ);
}
}
}
}
}
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咱們來看一下服務端的邏輯
一、服務端註冊到selector,而後interest set(ops)設置爲SelectionKey.OP_ACCEPT等待客戶端鏈接。
二、客戶端鏈接到達,調用到selectionKey.isAcceptable()方法,接收客戶端鏈接,而後得到一個channel,並把
interest set設置爲SelectionKey.OP_READ等待從通道中讀數據。
三、當客戶端發送的數據到達,selectionKey.isReadable() 被觸發,接收客戶端的數據並打印,而後把selectionKey.interestOps 設置爲SelectionKey.OP_WRITE,向客戶端發送數據。
四、當可寫以後selectionKey.isWritable()被觸發,向客戶端發送數據,同時selectionKey.interestOps再次設置爲
SelectionKey.OP_READ等待客戶端數據到達。
客戶端:
public static void main(String[] args) throws IOException {
SocketChannel socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
Selector selector = Selector.open();
socketChannel.register(selector, SelectionKey.OP_CONNECT);
socketChannel.connect(new InetSocketAddress("127.0.0.1", 9000));
while (true) {
int select = selector.select();
if (select > 0) {
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while (iterator.hasNext()) {
SelectionKey selectionKey = iterator.next();
if (selectionKey.isConnectable()) {
System.err.println("Connectable");
SocketChannel clientChannel = (SocketChannel) selectionKey.channel();
clientChannel.finishConnect();
selectionKey.interestOps(SelectionKey.OP_WRITE);
} else if (selectionKey.isReadable()) {
System.out.println("Readable");
SocketChannel channel = (SocketChannel) selectionKey.channel();
ByteBuffer buffer = ByteBuffer.allocate(128);
channel.read(buffer);
selectionKey.interestOps(SelectionKey.OP_WRITE);
System.out.println("收到服務端數據" + new String(buffer.array()));
} else if (selectionKey.isWritable()) {
SocketChannel clientChannel = (SocketChannel) selectionKey.channel();
String str = "qiwoo mobile";
ByteBuffer buffer = ByteBuffer.wrap(str.getBytes());
clientChannel.write(buffer);
selectionKey.interestOps(SelectionKey.OP_READ);
System.out.println("向服務端發送數據" + new String(buffer.array()));
}
iterator.remove();
}
}
}
}
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再來看一下服務端的邏輯
一、向服務端發起鏈接請求。
二、selectionKey.isConnectable()被觸發,鏈接成功以後,selectionKey.interestOps設置爲SelectionKey.OP_WRITE,準備向服務端發送數據。
三、channel可寫以後selectionKey.isWritable()被觸發,向服務端發送數據,以後selectionKey.interestOps設置爲SelectionKey.OP_READ,等待服務端過來的數據。
四、服務端數據發過來以後,selectionKey.isReadable()被觸發,讀取服務端數據以後selectionKey.interestOps設置爲SelectionKey.OP_WRITE向服務端寫數據。