第一章 java nio三大组件与使用姿势

Posted 2020-11-19 赵计刚

本案例来源于《netty权威指南》

一、三大组件

• Selector：多路复用器。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（accept接收连接事件、connect连接完成事件、read读事件、write写事件），从阻塞状态返回就绪的Channel的SelectionKey集合，之后进行IO操作。
• Channel：封装了socket。
  • ServerSocketChannel：封装了ServerSocket，用于accept客户端连接请求；
  • SocketChannel：一对SocketChannel组成一条虚电路，进行读写通信
• Buffer：用于存取数据，最主要的是ByteBuffer
  • position：下一个将被操作的字节位置
  • limit：在写模式下表示可以进行写的字节数，在读模式下表示可以进行读的字节数
  • capacity：Buffer的大小

 

二、服务端代码

1、服务端启动类

1 public class Server {
2     public static void main(String[] args) throws IOException {
3         new Thread(new ServerHandler(8080), "server-1").start();
4     }
5 }

创建一个任务ServerHandler，然后创建一条线程，启动执行该任务。

2、逻辑处理类

 1 public class ServerHandler implements Runnable {
 2     private Selector selector;
 3     private ServerSocketChannel ssChannel;
 4 
 5     public ServerHandler(int port) {
 6         try {
 7             //等价于 Selector selector = SelectorProvider.provider().openSelector();
 8             selector = Selector.open();
 9             //等价于 SelectorProvider.provider().openServerSocketChannel()
10             ssChannel = ServerSocketChannel.open();
11             ssChannel.configureBlocking(false);
12             ssChannel.bind(new InetSocketAddress(port), 1024);
13             ssChannel.register(selector, SelectionKey.OP_ACCEPT);
14         } catch (IOException e) {
15             e.printStackTrace();
16             System.exit(1);
17         }
18     }
19 
20     public void run() {
21         for (; ; ) {
22             try {
23                 selector.select();
24                 Iterator<SelectionKey> it = selector.selectedKeys().iterator();
25                 while (it.hasNext()) {
26                     SelectionKey key = it.next();
27                     it.remove();
28                     handleInput(key);
29                 }
30             } catch (Throwable t) {
31                 t.printStackTrace();
32             }
33         }
34 
35     }
36 
37     private void handleInput(SelectionKey key) throws IOException {
38         if (key.isValid()) {
39             // 处理新接入的请求消息
40             if (key.isAcceptable()) {
41                 // Accept the new connection
42                 ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
43                 SocketChannel sc = ssc.accept();
44                 sc.configureBlocking(false);
45                 // Add the new connection to the selector
46                 sc.register(selector, SelectionKey.OP_READ);
47             }
48             if (key.isReadable()) {
49                 // Read the data
50                 SocketChannel sc = (SocketChannel) key.channel();
51                 ByteBuffer readBuffer = ByteBuffer.allocate(1024);
52                 int readBytes = sc.read(readBuffer);
53                 if (readBytes > 0) {
54                     readBuffer.flip();
55                     byte[] bytes = new byte[readBuffer.remaining()];
56                     readBuffer.get(bytes);
57                     String body = new String(bytes, "UTF-8");
58                     System.out.println("The time server receive order : "
59                             + body);
60                     String currentTime = "QUERY TIME ORDER"
61                             .equalsIgnoreCase(body) ? new java.util.Date(
62                             System.currentTimeMillis()).toString()
63                             : "BAD ORDER";
64                     doWrite(sc, currentTime);
65                 } else if (readBytes < 0) {
66                     // 对端链路关闭
67                     key.cancel();
68                     sc.close();
69                 } else
70                     ; // 读到0字节，忽略
71             }
72         }
73     }
74 
75     private void doWrite(SocketChannel channel, String response)
76             throws IOException {
77         if (response != null && response.trim().length() > 0) {
78             byte[] bytes = response.getBytes();
79             ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
80             writeBuffer.put(bytes);
81             writeBuffer.flip();
82             channel.write(writeBuffer);
83         }
84     }
85 }

步骤：

1、创建一个Selector和ServerSocketChannel实例

2、配置ServerSocketChannel实例为非阻塞

3、ServerSocketChannel实例bind端口

4、将ServerSocketChannel实例注册到selector上，监听OP_ACCEPT事件

下面的任务在Server创建的新的线程中执行，不影响主线程执行其他逻辑

5、之后进入死循环

5.1、使用select.select()阻塞等待就绪事件（这里是等待OP_ACCEPT事件），一旦有有就绪事件到达，立即向下执行

5.2、使用selector.selectedKeys()获取已经就绪的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之后循环遍历

5.3、从迭代器删除该SelectionKey，防止下一次再被遍历到

5.4、如果SelectionKey==OP_ACCEPT，则通过ServerSocketChannel.accept()创建SocketChannel，该SocketChannel是后续真正的与客户端的SocketChannel进行通信的实体

5.5、配置新创建的SocketChannel实例为非阻塞，然后将该SocketChannel实例注册到selector实例上，监听OP_READ事件

5.6、等客户端发出请求数据时，此处监听到SelectionKey==OP_READ，则创建ByteBuffer实例，将SocketChannel中的数据读取到ByteBuffer中，然后再创建ByteBuffer将信息写回到SocketChannel（也就是说数据的读写一定要通过Buffer）

 

三、客户端代码

1、客户端启动类

1 public class Client {
2     public static void main(String[] args) {
3         new Thread(new ClientHandler("127.0.0.1", 8080), "client-1").start();
4     }
5 }

创建一个任务ClientHandler，然后创建一条线程，启动执行该任务。

2、逻辑处理类

 1 public class ClientHandler implements Runnable {
 2     private String host;
 3     private int port;
 4 
 5     private Selector selector;
 6     private SocketChannel socketChannel;
 7 
 8     public ClientHandler(String host, int port) {
 9         this.host = host;
10         this.port = port;
11         try {
12             selector = Selector.open();
13             socketChannel = SocketChannel.open();
14             socketChannel.configureBlocking(false);
15         } catch (IOException e) {
16             e.printStackTrace();
17             System.exit(1);
18         }
19     }
20 
21     public void run() {
22         try {
23             doConnect();
24         } catch (IOException e) {
25             e.printStackTrace();
26             System.exit(1);
27         }
28         while (true) {
29             try {
30                 selector.select();
31                 Iterator<SelectionKey> it = selector.selectedKeys().iterator();
32                 while (it.hasNext()) {
33                     SelectionKey key = it.next();
34                     it.remove();
35                     handleInput(key);
36                 }
37             } catch (Exception e) {
38                 e.printStackTrace();
39                 System.exit(1);
40             }
41         }
42     }
43 
44     private void handleInput(SelectionKey key) throws IOException {
45         if (key.isValid()) {
46             // 判断是否连接成功
47             SocketChannel sc = (SocketChannel) key.channel();
48             if (key.isConnectable()) {
49                 if (sc.finishConnect()) {
50                     sc.register(selector, SelectionKey.OP_READ);
51                     doWrite(sc);
52                 } else
53                     System.exit(1);// 连接失败，进程退出
54             } else if (key.isReadable()) {
55                 ByteBuffer readBuffer = ByteBuffer.allocate(1024);
56                 int readBytes = sc.read(readBuffer);
57                 if (readBytes > 0) {
58                     readBuffer.flip();
59                     byte[] bytes = new byte[readBuffer.remaining()];
60                     readBuffer.get(bytes);
61                     String body = new String(bytes, "UTF-8");
62                     System.out.println("Now is : " + body);
63                 } else if (readBytes < 0) {
64                     // 对端链路关闭
65                     key.cancel();
66                     sc.close();
67                 } else
68                     ; // 读到0字节，忽略
69             }
70         }
71 
72     }
73 
74     private void doConnect() throws IOException {
75         // 如果直接连接成功，则注册到多路复用器上，发送请求消息，读应答
76         if (socketChannel.connect(new InetSocketAddress(host, port))) {
77             socketChannel.register(selector, SelectionKey.OP_READ);
78             doWrite(socketChannel);
79         } else
80             socketChannel.register(selector, SelectionKey.OP_CONNECT);
81     }
82 
83     private void doWrite(SocketChannel sc) throws IOException {
84         byte[] req = "QUERY TIME ORDER".getBytes();
85         ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
86         writeBuffer.put(req);
87         writeBuffer.flip();
88         sc.write(writeBuffer);
89         if (!writeBuffer.hasRemaining())
90             System.out.println("Send order 2 server succeed.");
91     }
92 }

步骤：

1、创建一个Selector和SocketChannel实例

2、配置SocketChannel实例为非阻塞

下面的任务在Cilent创建的新的线程中执行，不影响主线程执行其他逻辑

3、SocketChannel.connect连接到server端，如果连接没有马上成功，将该SocketChannel实例注册到selector上，监听OP_CONNECT事件；如果连接成功，将该SocketChannel实例注册到selector上，监听OP_READ事件，之后写数据给server端

4、之后进入死循环

4.1、使用select.select()阻塞等待就绪事件，一旦有有就绪事件到达，立即向下执行

4.2、使用selector.selectedKeys()获取已经就绪的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之后循环遍历

4.3、从迭代器删除该SelectionKey，防止下一次再被遍历到

4.4、如果SelectionKey==OP_CONNECT，将该SocketChannel实例注册到selector上，监听OP_READ事件，之后写数据给server端；如果监听到SelectionKey==OP_READ，则创建ByteBuffer实例，将SocketChannel中的数据读取到ByteBuffer中