Java IO与NIO的对比与高级用法

在Java中，I/O操作（输入/输出操作）是非常基础且重要的一部分。Java提供了两种主要的I/O API：传统的IO（java.io包）和新IO（NIO，java.nio包）。这两者在设计理念、性能和使用场景上有显著的不同。本文将深入探讨Java IO与NIO的对比，并提供一些高级用法的示例代码。

1. Java IO与NIO的基本概念

1.1 Java IO

Java IO API是基于流（Stream）的模型。它以同步和阻塞的方式进行数据读写操作。每次I/O操作都会阻塞调用线程，直到操作完成。这种方式简单直观，但在高并发场景下性能表现不佳。

1.2 Java NIO

Java NIO（Non-blocking IO）引入了一种基于缓冲区（Buffer）和通道（Channel）的模型。NIO支持非阻塞模式，可以在进行I/O操作时不中断线程，从而提高了性能和可扩展性。NIO还引入了选择器（Selector）用于管理多个通道的非阻塞I/O操作。

2. Java IO与NIO的对比

特性	Java IO	Java NIO
模型	基于流 (Stream)	基于缓冲区 (Buffer) 和通道 (Channel)
阻塞/非阻塞	阻塞I/O	非阻塞I/O
数据处理	字节/字符流	缓冲区中读取和写入数据
性能	简单，但在高并发下性能较差	在高并发和大数据处理场景下性能更佳
API复杂度	较为简单	复杂度较高

3. Java IO的高级用法

3.1 文件读写操作

import java.io.*;public class FileIODemo {public static void main(String[] args) {String filePath = "example.txt";try (BufferedWriter writer = new BufferedWriter(new FileWriter(filePath))) {writer.write("Hello, Java IO!");} catch (IOException e) {e.printStackTrace();}try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {String line;while ((line = reader.readLine()) != null) {System.out.println(line);}} catch (IOException e) {e.printStackTrace();}}
}

3.2 网络通信（Socket编程）

import java.io.*;
import java.net.*;public class SocketIODemo {public static void main(String[] args) {// Servernew Thread(() -> {try (ServerSocket serverSocket = new ServerSocket(8080)) {Socket socket = serverSocket.accept();BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);writer.println("Hello, Client!");System.out.println("Client says: " + reader.readLine());} catch (IOException e) {e.printStackTrace();}}).start();// Clientnew Thread(() -> {try (Socket socket = new Socket("localhost", 8080)) {BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);System.out.println("Server says: " + reader.readLine());writer.println("Hello, Server!");} catch (IOException e) {e.printStackTrace();}}).start();}
}

4. Java NIO的高级用法

4.1 文件读写操作

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;public class FileNIODemo {public static void main(String[] args) {String filePath = "example_nio.txt";Path path = Paths.get(filePath);String content = "Hello, Java NIO!";// Write to file using NIOtry (FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {ByteBuffer buffer = ByteBuffer.allocate(1024);buffer.put(content.getBytes());buffer.flip();fileChannel.write(buffer);} catch (IOException e) {e.printStackTrace();}// Read from file using NIOtry (FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.READ)) {ByteBuffer buffer = ByteBuffer.allocate(1024);fileChannel.read(buffer);buffer.flip();byte[] bytes = new byte[buffer.remaining()];buffer.get(bytes);System.out.println(new String(bytes));} catch (IOException e) {e.printStackTrace();}}
}

4.2 网络通信（Socket编程）

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;public class SocketNIODemo {public static void main(String[] args) {new Thread(SocketNIODemo::startServer).start();new Thread(SocketNIODemo::startClient).start();}public static void startServer() {try (Selector selector = Selector.open();ServerSocketChannel serverChannel = ServerSocketChannel.open()) {serverChannel.bind(new InetSocketAddress(8081));serverChannel.configureBlocking(false);serverChannel.register(selector, SelectionKey.OP_ACCEPT);while (true) {selector.select();Iterator<SelectionKey> keys = selector.selectedKeys().iterator();while (keys.hasNext()) {SelectionKey key = keys.next();keys.remove();if (key.isAcceptable()) {ServerSocketChannel server = (ServerSocketChannel) key.channel();SocketChannel client = server.accept();client.configureBlocking(false);client.register(selector, SelectionKey.OP_READ);ByteBuffer buffer = ByteBuffer.wrap("Hello, Client!".getBytes());client.write(buffer);} else if (key.isReadable()) {SocketChannel client = (SocketChannel) key.channel();ByteBuffer buffer = ByteBuffer.allocate(256);client.read(buffer);buffer.flip();byte[] bytes = new byte[buffer.remaining()];buffer.get(bytes);System.out.println("Client says: " + new String(bytes));}}}} catch (IOException e) {e.printStackTrace();}}public static void startClient() {try (SocketChannel clientChannel = SocketChannel.open(new InetSocketAddress("localhost", 8081))) {clientChannel.configureBlocking(false);ByteBuffer buffer = ByteBuffer.allocate(256);while (clientChannel.read(buffer) <= 0) {// Wait for server response}buffer.flip();byte[] bytes = new byte[buffer.remaining()];buffer.get(bytes);System.out.println("Server says: " + new String(bytes));buffer.clear();buffer.put("Hello, Server!".getBytes());buffer.flip();while (buffer.hasRemaining()) {clientChannel.write(buffer);}} catch (IOException e) {e.printStackTrace();}}
}