How does NIO technology handle non-blocking IO operations in Java functions?

NIO technology handles non-blocking IO operations and uses event-driven mechanisms to process I/O asynchronously to improve efficiency in high concurrent request scenarios. Manage IO operations by defining channels, creating Selectors, registering channels to Selectors, listening to events, and handling event steps. The practical case shows a server-side non-blocking Echo program that uses NIO to asynchronously accept and respond to client connection requests.

NIO technology in Java functions handles non-blocking IO operations

NIO (non-blocking IO) is an efficient way to To handle high concurrent requests in large network applications, it uses a non-blocking mode to handle I/O asynchronously through an event-driven mechanism. NIO API is provided in Java to describe NIO events, channels and buffers.

1. Define NIO channel

A channel in NIO represents an open file or network connection. There are four main types of channels:

import java.nio.channels.*;

// 文件通道
FileChannel fileChannel = FileChannel.open(Paths.get("file.txt"), StandardOpenOption.READ);

// 套接字通道
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();

// 套接字通道
SocketChannel socketChannel = SocketChannel.open();

// 套接字通道
DatagramChannel datagramChannel = DatagramChannel.open();

2. Create Selectors

Selectors are used to monitor events on multiple channels. They can handle a large number of connections from different channels simultaneously, thereby managing IO operations efficiently.

import java.nio.channels.Selector;

Selector selector = Selector.open();

3. Register the channel

Register the channel to the Selector to monitor events of interest, such as read/write operations.

serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

4. Listening for events

Use the select() method to monitor events in the Selector until an event occurs. This method blocks until at least one channel is ready for processing.

int numKeys = selector.select();

5. Handle events

Handle events that occur by checking SelectionKey, which provides information about the channel and type of the event that occurred details.

for (SelectionKey key : selector.selectedKeys()) {
    if (key.isAcceptable()) {
        // 监听新的连接请求
    } else if (key.isReadable()) {
        // 读取数据
    } else if (key.isWritable()) {
        // 写入数据
    }
}

Practical case: Server-side non-blocking Echo program

This example creates a server that uses NIO to asynchronously accept and respond to client connections.

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;

public class NonBlockingEchoServer {

    public static void main(String[] args) throws IOException {
        // 创建一个 ServerSocketChannel
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8080));
        serverSocketChannel.configureBlocking(false);

        // 创建一个 Selector
        Selector selector = Selector.open();

        // 注册 ServerSocketChannel 到 Selector，监视 ACCEPT 事件
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        while (true) {
            // 监听事件
            selector.select();

            // 获取选择的 SelectionKey 集合
            Set<SelectionKey> selectedKeys = selector.selectedKeys();

            // 遍历选择的 SelectionKey
            Iterator<SelectionKey> iterator = selectedKeys.iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();

                if (key.isAcceptable()) {
                    // 新的连接请求
                    SocketChannel socketChannel = serverSocketChannel.accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    // 读取数据
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    ByteBuffer buffer = ByteBuffer.allocate(1024);
                    int readBytes = socketChannel.read(buffer);
                    if (readBytes > 0) {
                        // 响应客户端消息
                        buffer.flip();
                        socketChannel.write(buffer);
                    }
                }

                // 从集合中删除处理过的 SelectionKey
                iterator.remove();
            }
        }
    }
}

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