NIO 的基本使用
yls 2020/5/23
NIO中buffer的使用
/**
* 测试 nio 中 buffer的使用
* buffer 内部就是一个数组 ： final int[] hb; 、
*
* buffer 定义了 position,capacity,limit,mark四个属性来标记buffer中的数据信息
* 可以通过debug的方式跟踪查看值的变化
* private int mark = -1; 标记
* private int position = 0; 下一个要被读或写的元素的索引，每次读写都会改变其值，为下次读写做准备
* private int limit; 表示缓冲区的当前终点，不能对超过limit限制的缓冲区别进行读写，limit可以修改
* private int capacity; 容量，创建buffer时设置，不能被改变
*
* buffer 读写切换时需要执行 flip（）方法
* public final Buffer flip() {
* limit = position;
* position = 0;
* mark = -1;
* return this;
* }
* buffer清除数据时调用 clear（）方法，只改变标记的指向位置，不真正删除底层数组的值
* public final Buffer clear() {
* position = 0;
* limit = capacity;
* mark = -1;
* return this;
* }
*/
public class BasicBuffer {
public static void main(String[] args) {
final IntBuffer intBuffer = IntBuffer.allocate(5);
for (int i = 0; i <intBuffer.capacity() ; i++) {
intBuffer.put(i*2);
}
intBuffer.flip();
for (int i = 0; i < intBuffer.capacity(); i++) {
System.out.println(intBuffer.get());
}
}
}
NIO中Socket通信实例
1.服务端
/**
* 同步 非阻塞
* FileChannel.transferTo实现了零拷贝，效率高，三十在windows中一次只能传8M,所以大文件需要断点续传
*/
public class NioServer {
public static void main(String[] args) throws IOException {
//创建一个ServerSocketChannel
final ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
//绑定一个端口，在服务端监听
serverSocketChannel.socket().bind(new InetSocketAddress(7777));
//设置为非阻塞
serverSocketChannel.configureBlocking(false);
//得到一个selector对象
Selector selector = Selector.open();
//serverSocketChannel注册到selector,关心 事件 OP_ACCEPT
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
//循环等待客户端连接
while (true) {
//等待一秒，若没有事件发生，返回
if (selector.select(1000) == 0) {
System.out.println("服务器等待了1秒，没有请求连接。。。。");
continue;
}
//若返回的值>0，说明已经获取到相关的事件，则获取到相关的selectionKeys集合
Set<SelectionKey> selectionKeys = selector.selectedKeys();
//使用迭代器遍历
Iterator<SelectionKey> iterator = selectionKeys.iterator();
while (iterator.hasNext()) {
//获取到相应的key
SelectionKey key = iterator.next();
//根据key对应的通道发生的事件做出处理
if (key.isAcceptable()) {//如果是 isAcceptable,有新的连接
//这里的key对应的channel一定是serverSocketChannel
//为该客户端生成一个socketChannel
SocketChannel socketChannel = serverSocketChannel.accept();
//将新生成的socketChannel设置为非阻塞模式，否则会抛出异常
socketChannel.configureBlocking(false);
//将socketChannel注册到selector,关心事件为OP_READ，并关联一个buffer
socketChannel.register(selector, SelectionKey.OP_READ, ByteBuffer.allocate(128));
}
if (key.isReadable()) { //发生 isReadable 事件，表示有新数据发送过来
//根据key反向获取到相应的channel
SocketChannel channel = (SocketChannel) key.channel();
//获取到channel关联的buffer
ByteBuffer byteBuffer = (ByteBuffer) key.attachment();
//先将buffer置于初始状态
byteBuffer.clear();
//将channel中的数据读到buffer中
channel.read(byteBuffer);
//buffer读写切换
byteBuffer.flip();
//从buffer中读有效数据到bytes
//byteBuffer.array()直接返回buffer底层数组，如果后面发送的数据比之前发送的少，会将之前获取的值获取出来
byte[] bytes = new byte[byteBuffer.limit()];
byteBuffer.get(bytes);
System.out.println("from 客户端： " + new String(bytes));
}
//手动从集合中移除当前的key，防止重复操作
iterator.remove();
}
}
}
}
2.客户端
public class NioClient {
public static void main(String[] args) throws IOException {
//获取一个 socketChannel
final SocketChannel socketChannel = SocketChannel.open();
//设置 socketChannel 非阻塞
socketChannel.configureBlocking(false);
//提供服务端的ip和端口，连接服务端，不阻塞
//通过 socketChannel.finishConnect() 判断是否连接成功
boolean connect = socketChannel.connect(new InetSocketAddress("127.0.0.1", 6999));
if (!connect) {
while (!socketChannel.finishConnect()) {
System.out.println("因为连接需要时间，客户端不会阻塞，可以做其它事情。。。");
}
}
//连接成功后。。。。
System.out.println("1...");
String s = "大忽忽";
// Wraps a byte array into a buffer
ByteBuffer byteBuffer = ByteBuffer.wrap(s.getBytes());
//发送数据
final int write = socketChannel.write(byteBuffer);
System.out.println("2....");
System.in.read();
}
}
NIO中Scattering、Gathering的使用
1.服务端
/**
* scattering: 分散，把数据写入buffer时，可以采用buffer数组，依次写
* gathering: 聚合，从buffer中读取数据时，可以采用buffer数组，依次读
*/
public class ScatteringAndGathering {
public static void main(String[] args) throws IOException {
//绑定端口到socket,并启动
final ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.socket().bind(new InetSocketAddress(7000));
//创建buffer数组
final ByteBuffer[] byteBuffers = new ByteBuffer[2];
byteBuffers[0] = ByteBuffer.allocate(4);
byteBuffers[1] = ByteBuffer.allocate(4);
//等待客户端连接，连接成功后生成SocketChannel
final SocketChannel socketChannel = serverSocketChannel.accept();
//循环读取
while (true) {
//从channel读取数据到buffer数组
long read = socketChannel.read(byteBuffers);
System.out.println("read=========" + read);
if (read == 0 || read == -1) {
break;
}
Arrays.asList(byteBuffers).forEach(buffer -> {
System.out.println("position=" + buffer.position() + ", limit=" + buffer.limit());
});
//读写切换
Arrays.asList(byteBuffers).forEach(buffer -> {
buffer.flip();
});
//将buffer数组中的数据写入channel,显示到客户端
final long write = socketChannel.write(byteBuffers);
//将每个buffer置于初始状态
Arrays.asList(byteBuffers).forEach(buffer -> {
buffer.clear();
});
}
}
}
2.客户端使用上边 Socket通信实例 中的就可以（改一下端口号）
NIO 使用 Socket通信实现一个群发系统
1.服务端
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;
/**
* 简单的群聊系统（NIO 实现）
* 服务端：可以监听客户端的上线和离线，可以接收客户端发送的数据并转发到其它客户端
* 客户端：可以不阻塞的发送数据和接收其它客户端发送的数据
*/
public class GroupChatServer {
private ServerSocketChannel serverSocketChannel;
private Selector selector;
private static final int port = 7999;
public GroupChatServer() throws IOException {
serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
serverSocketChannel.socket().bind(new InetSocketAddress(port));
selector = Selector.open();
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
}
//监听
public void listen() {
try {
while (true) {
final int select = selector.select(2000);
if (select > 0) {//有事件发生
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while (iterator.hasNext()) {
//获取key
SelectionKey key = iterator.next();
//根据key对应的通道发生的事件做出处理
if (key.isAcceptable()) {//如果是 isAcceptable,有新的连接
//这里的key对应的channel一定是serverSocketChannel
//为该客户端生成一个socketChannel
// SocketChannel socketChannel = serverSocketChannel.accept();
SocketChannel socketChannel = ((ServerSocketChannel) key.channel()).accept();
//将新生成的socketChannel设置为非阻塞模式，否则会抛出异常
socketChannel.configureBlocking(false);
//将socketChannel注册到selector,关心事件为OP_READ，并关联一个buffer
socketChannel.register(selector, SelectionKey.OP_READ);
//提示
System.out.println(socketChannel.getRemoteAddress() + ",上线了");
}
if (key.isReadable()) { //发生 isReadable 事件，表示有新数据发送过来
//专门写方法，处理读操作
readData(key);
}
//手动从集合中移除当前的key，防止重复操作
iterator.remove();
}
} else {
System.out.println("等待。。。");
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
private void readData(SelectionKey key) {
SocketChannel channel = null;
try {
//根据key反向获取到相应的channel
channel = (SocketChannel) key.channel();
ByteBuffer byteBuffer = ByteBuffer.allocate(128);
//将channel中的数据读到buffer中
final int read = channel.read(byteBuffer);
String msg = new String(byteBuffer.array(), 0, read);
System.out.println("from 客户端： " + msg);
//转发消息到其它客户端（除了自己），专门写一个方法
sendMsgToOthers(msg, channel);
} catch (Exception e) {
e.printStackTrace();
try {
System.out.println(channel.getRemoteAddress() + "离线了。。");
//关闭通道
channel.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
private void sendMsgToOthers(String msg, SocketChannel self) {
final Set<SelectionKey> keys = selector.keys();
keys.forEach((key) -> {
SelectableChannel channel = key.channel();
if (channel instanceof SocketChannel && channel != self) {
SocketChannel socketChannel=(SocketChannel)channel;
final ByteBuffer buffer = ByteBuffer.wrap(msg.getBytes());
try {
socketChannel.write(buffer);
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
public static void main(String[] args) throws IOException {
final GroupChatServer groupChatServer = new GroupChatServer();
groupChatServer.listen();
}
}
2.客户端
public class GroupChatClient {
private String ip = "127.0.0.1";
private int port = 7999;
private Selector selector;
private SocketChannel socketChannel;
private String name;
public GroupChatClient() throws IOException {
socketChannel = SocketChannel.open(new InetSocketAddress(ip, port));
socketChannel.configureBlocking(false);
selector = Selector.open();
socketChannel.register(selector, SelectionKey.OP_READ);
name = socketChannel.getLocalAddress().toString().substring(1);
System.out.println(name + " is start ..");
}
//发送消息
public void sendData(String msg) throws IOException {
msg = name + " 说：" + msg;
socketChannel.write(ByteBuffer.wrap(msg.getBytes()));
}
//接收消息
public void rec() {
try {
while (true) {
final int select = selector.select();
if (select > 0) {
final Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while (iterator.hasNext()) {
final SelectionKey next = iterator.next();
if (next.isReadable()) {
SocketChannel channel = (SocketChannel) next.channel();
final ByteBuffer allocate = ByteBuffer.allocate(128);
final int read = channel.read(allocate);
System.out.println(new String(allocate.array(), 0, read));
}
iterator.remove();
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws IOException {
final GroupChatClient groupChatClient = new GroupChatClient();
//一个线程专门接收数据
new Thread(() -> {
groupChatClient.rec();
}, "接收数据线程").start();
//主线程用来发送数据
final Scanner scanner = new Scanner(System.in);
while (scanner.hasNext()) {
final String s = scanner.nextLine();
groupChatClient.sendData(s);
}
}
}
