Java 网络编程之TCP(五)：分析服务端注册OP_WRITE写数据的各种场景（一）

在前面的文章中，我们分析了在NIO模式下，服务端接收和读取多个客户端数据的情况；

本文，我们看下NIO模式下，使用Selector如何把数据发送给客户端。

一、直接通过java.nio.channels.SocketChannel#write(java.nio.ByteBuffer)方法写

二、注册OP_WRITE，在写状态满足情况下，通过java.nio.channels.SocketChannel#write(java.nio.ByteBuffer)方法写

我们看下第一种情况：

服务端在有数据需要发送给客户端的情况下，直接使用客户端对应的SocketChannel写数据即可，不考虑数据是否可以正常发送。

这和BIO下，直接通过输出流写数据是一样的

我们可以基于聊天室的功能，把收到的数据直接写给其他客户端

客户端代码统一使用BIO，如下：

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;/*** 基于BIO的TCP网络通信的客户端，接收控制台输入的数据，然后通过字节流发送给服务端**/
class ChatClient {public static void main(String[] args) throws IOException {// 连接serverSocket serverSocket = new Socket("localhost", 9090);System.out.println("client connected to server");// 读取用户在控制台上的输入，并发送给服务器new Thread(new ClientThread(serverSocket)).start();// 接收服务端发送过来的数据try (InputStream serverSocketInputStream = serverSocket.getInputStream();) {byte[] buffer = new byte[1024];int len;while ((len = serverSocketInputStream.read(buffer)) != -1) {String data = new String(buffer, 0, len);System.out.println("client receive data from server" + serverSocketInputStream + " data size：" + len + ": " + data);}}}
}class ClientThread implements Runnable {private Socket serverSocket;public ClientThread(Socket serverSocket) {this.serverSocket = serverSocket;}@Overridepublic void run() {// 读取用户在控制台上的输入，并发送给服务器InputStream in = System.in;byte[] buffer = new byte[1024];int len;try (OutputStream outputStream = serverSocket.getOutputStream();) {// read操作阻塞，直到有数据可读，由于后面还要接收服务端转发过来的数据，这两个操作都是阻塞的，所以需要两个线程while ((len = in.read(buffer)) != -1) {String data = new String(buffer, 0, len);System.out.println("client receive data from console" + in + " : " + new String(buffer, 0, len));if ("exit\n".equals(data)) {// 模拟客户端关闭连接System.out.println("client close :" + serverSocket);// 这里跳出循环后，try-with-resources 会自动关闭outputStreambreak;}// 发送数据给服务器端outputStream.write(new String(buffer, 0, len).getBytes()); // 此时buffer中是有换行符}} catch (IOException e) {throw new RuntimeException(e);}}
}

服务端代码如下：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;/*** 基于NIO实现服务端，通过Selector基于事件驱动客户端的读取* 服务端接收到数据后，直接写回客户端，或者写给其他客户端**/
class NIOSelectorDirectWriteServer {Selector selector;public static void main(String[] args) throws IOException {NIOSelectorDirectWriteServer server = new NIOSelectorDirectWriteServer();server.start(); // 开启监听和事件处理}public void start() {initServer();// selector非阻塞轮询有哪些感兴趣的事件到了doService();}private void doService() {if (selector == null) {System.out.println("server init failed, without doing read/write");return;}try {while (true) {while (selector.select() > 0) {Set<SelectionKey> keys = selector.selectedKeys(); // 感兴趣且准备好的事件Iterator<SelectionKey> iterator = keys.iterator(); // 迭代器遍历处理，后面要删除集合元素while (iterator.hasNext()) {SelectionKey key = iterator.next();iterator.remove(); // 删除当前元素，防止重复处理// 下面根据事件进行分别处理if (key.isAcceptable()) {// 客户端连接事件acceptHandler(key);} else if (key.isReadable()) {// 读取客户端数据readHandler(key);}}}}} catch (IOException exception) {exception.printStackTrace();}}private void initServer() {try {ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();serverSocketChannel.configureBlocking(false);serverSocketChannel.bind(new InetSocketAddress(9090));// 此时在selector上注册感兴趣的事件// 这里先注册OP_ACCEPT: 客户端连接事件selector = Selector.open();serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);System.out.println("server init success");} catch (IOException exception) {exception.printStackTrace();System.out.println("server init failied");}}public void acceptHandler(SelectionKey key) {ServerSocketChannel server = (ServerSocketChannel) key.channel(); // 获取客户端的channeltry {SocketChannel client = server.accept();client.configureBlocking(false); // 设置client非阻塞System.out.println("server receive a client :" + client);// 注册OP_READ事件，用于从客户端读取数据// 给Client分配一个buffer，用于读取数据，注意buffer的线程安全ByteBuffer buffer = ByteBuffer.allocate(1024); // buffer这个参数注册的时候也可以不用client.register(key.selector(), SelectionKey.OP_READ, buffer);} catch (IOException exception) {exception.printStackTrace();}}public void readHandler(SelectionKey key) {System.out.println("read handler");SocketChannel client = (SocketChannel) key.channel(); // 获取客户端的channelByteBuffer buffer = (ByteBuffer) key.attachment(); // 获取Client channel关联的bufferbuffer.clear(); // 使用前clear// 防止数据分包，需要while循环读取try {while (true) {int readLen = client.read(buffer);if (readLen > 0) {// 读取到数据了buffer.flip();byte[] data = new byte[buffer.limit()];buffer.get(data);System.out.println("server read data from " + client + ", data is :" + new String(data));// 转发给其他客户端forwardMsg(client, data);} else if (readLen == 0) {// 没读到数据System.out.println(client + " : no data");break;} else if (readLen < 0) {// client 关闭连接// 当客户端主动连接断开时，为了让服务器知道断开了连接，会产生OP_READ事件。所以需要判断读取长度，当读到-1时，关闭channel。System.out.println(client + " close");client.close();break;}}} catch (IOException exception) {exception.printStackTrace();// client 关闭连接System.out.println(client + " disconnect");// todo:disconnect 导致一直有read事件，怎么办？try {client.close();} catch (IOException ex) {System.out.println("close ex");}}}private void forwardMsg(SocketChannel myself, byte[] msg) throws IOException {Set<SelectionKey> keys = selector.keys();// read/write 对应同一个key，同一个client不会发送两遍for (SelectionKey key : keys) {SelectableChannel channel = key.channel();if (channel instanceof SocketChannel && channel != myself) {// 发送数据SocketChannel client = (SocketChannel) channel;System.out.println("forward msg to " + client);ByteBuffer buff = ByteBuffer.wrap(msg);while (buff.hasRemaining()) {client.write(buff);}}}}
}

可以看到，这里我们在forwardMsg()方法中，直接通过channel 把数据转发出去了

测试：

先启动服务器，然后启动两个客户端

客户端1发送消息client1，服务端接收到后转发给客户端2

客户端2发送消息client2，服务端接收到后转发给客户端1

服务端日志：

server init success
server receive a client :java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23536]
server receive a client :java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23549]
read handler
server read data from java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23536], data is :client1forward msg to java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23549]
java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23536] : no data
read handler
server read data from java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23549], data is :client2forward msg to java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23536]
java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23549] : no data

客户端1日志：

client connected to server
client1
client receive data from consolejava.io.BufferedInputStream@65231a33 : client1client receive data from serverjava.net.Socket$SocketInputStream@4629104a data size：8: client2

客户端2日志：

client connected to server
client receive data from serverjava.net.Socket$SocketInputStream@27f8302d data size：8: client1client2
client receive data from consolejava.io.BufferedInputStream@72cdfe9a : client2

测试：客户端1 正常退出关闭

客户端1日志：

exit
client receive data from consolejava.io.BufferedInputStream@65231a33 : exitclient close :Socket[addr=localhost/127.0.0.1,port=9090,localport=23536]
Exception in thread "main" java.net.SocketException: Socket closedat java.base/sun.nio.ch.NioSocketImpl.endRead(NioSocketImpl.java:248)at java.base/sun.nio.ch.NioSocketImpl.implRead(NioSocketImpl.java:327)at java.base/sun.nio.ch.NioSocketImpl.read(NioSocketImpl.java:350)at java.base/sun.nio.ch.NioSocketImpl$1.read(NioSocketImpl.java:803)at java.base/java.net.Socket$SocketInputStream.read(Socket.java:966)at java.base/java.io.InputStream.read(InputStream.java:218)at com.huawei.io.chatroom.bio.ChatClient.main(ChatClient.java:29)Process finished with exit code 1

服务端日志：

read handler
java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23536] close

测试：客户端2异常断开

服务端日志：

read handler
java.nio.channels.SocketChannel[connected local=/127.0.0.1:9090 remote=/127.0.0.1:23549] disconnect
java.net.SocketException: Connection resetat java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(SocketChannelImpl.java:394)at java.base/sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:426)at com.huawei.io.chatroom.nio.sel.NIOSelectorDirectWriteServer.readHandler(NIOSelectorDirectWriteServer.java:107)at com.huawei.io.chatroom.nio.sel.NIOSelectorDirectWriteServer.doService(NIOSelectorDirectWriteServer.java:56)at com.huawei.io.chatroom.nio.sel.NIOSelectorDirectWriteServer.start(NIOSelectorDirectWriteServer.java:34)at com.huawei.io.chatroom.nio.sel.NIOSelectorDirectWriteServer.main(NIOSelectorDirectWriteServer.java:28)

二、注册OP_WRITE写数据