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字节流

输入流（InputStream）

FileInputStream：从文件系统中读取原始字节

import java.io.FileInputStream;
import java.io.IOException;public class ReadFileBytes {public static void main(String[] args) {try (FileInputStream fis = new FileInputStream("input.txt")) {int content;while ((content = fis.read()) != -1) {System.out.print((char) content);}} catch (IOException e) {e.printStackTrace();}}
}

ByteArrayInputStream：允许程序从一个字节数组中读取数据

import java.io.ByteArrayInputStream;public class ReadByteArray {public static void main(String[] args) {byte[] buffer = "Hello, World!".getBytes();try (ByteArrayInputStream bis = new ByteArrayInputStream(buffer)) {int data;while ((data = bis.read()) != -1) {System.out.print((char) data);}}}
}

BufferedInputStream：为其他输入流添加缓冲功能

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;public class BufferedRead {public static void main(String[] args) {try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream("input.txt"))) {int content;while ((content = bis.read()) != -1) {System.out.print((char) content);}} catch (IOException e) {e.printStackTrace();}}
}

ObjectInputStream：用于反序列化对象

import java.io.ObjectInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.Serializable;class Person implements Serializable {private static final long serialVersionUID = 1L;String name;Person(String name) {this.name = name;}
}public class DeserializeObject {public static void main(String[] args) {try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream("person.ser"))) {Person person = (Person) ois.readObject();System.out.println(person.name);} catch (IOException | ClassNotFoundException e) {e.printStackTrace();}}
}

输出流（OutputStream）

FileOutputStream：向文件系统中的文件写入原始字节

import java.io.FileOutputStream;
import java.io.IOException;public class WriteFileBytes {public static void main(String[] args) {String data = "Hello, World!";byte[] buffer = data.getBytes();try (FileOutputStream fos = new FileOutputStream("output.txt")) {fos.write(buffer);} catch (IOException e) {e.printStackTrace();}}
}

ByteArrayOutputStream：将输出的数据写入到字节数组中

import java.io.ByteArrayOutputStream;public class WriteByteArray {public static void main(String[] args) {String data = "Hello, World!";byte[] buffer = data.getBytes();try (ByteArrayOutputStream baos = new ByteArrayOutputStream()) {baos.write(buffer);byte[] output = baos.toByteArray();System.out.println(new String(output));}}
}

BufferedOutputStream：为其他输出流提供缓冲区

import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;public class BufferedWrite {public static void main(String[] args) {String data = "Hello, World!\n";byte[] buffer = data.getBytes();try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("output.txt"))) {bos.write(buffer);} catch (IOException e) {e.printStackTrace();}}
}

ObjectOutputStream：用于序列化对象

import java.io.ObjectOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.Serializable;class Person implements Serializable {private static final long serialVersionUID = 1L;String name;Person(String name) {this.name = name;}
}public class SerializeObject {public static void main(String[] args) {Person person = new Person("Alice");try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("person.ser"))) {oos.writeObject(person);} catch (IOException e) {e.printStackTrace();}}
}

字符流

输入流（Reader）

FileReader：简化了从文件读取字符的过程

import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;public class ReadFileChars {public static void main(String[] args) {try (BufferedReader reader = new BufferedReader(new FileReader("input.txt"))) {String line;while ((line = reader.readLine()) != null) {System.out.println(line);}} catch (IOException e) {e.printStackTrace();}}
}

CharArrayReader：从字符数组中读取字符

import java.io.CharArrayReader;public class ReadCharArray {public static void main(String[] args) {char[] chars = "Hello, World!".toCharArray();try (CharArrayReader car = new CharArrayReader(chars)) {int c;while ((c = car.read()) != -1) {System.out.print((char) c);}}}
}

BufferedReader：为其他字符输入流添加缓冲区

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;public class BufferedCharRead {public static void main(String[] args) {try (BufferedReader br = new BufferedReader(new FileReader("input.txt"))) {String line;while ((line = br.readLine()) != null) {System.out.println(line);}} catch (IOException e) {e.printStackTrace();}}
}

InputStreamReader：桥接器，将字节流转换为字符流

import java.io.InputStreamReader;
import java.io.FileInputStream;
import java.io.IOException;public class ByteToChar {public static void main(String[] args) {try (InputStreamReader isr = new InputStreamReader(new FileInputStream("input.txt"), "UTF-8")) {int c;while ((c = isr.read()) != -1) {System.out.print((char) c);}} catch (IOException e) {e.printStackTrace();}}
}

输出流（Writer）

FileWriter：简化了将字符写入文件的过程

import java.io.FileWriter;
import java.io.IOException;public class WriteFileChars {public static void main(String[] args) {String data = "Hello, World!\n";try (FileWriter writer = new FileWriter("output.txt", true)) { // 追加模式writer.write(data);} catch (IOException e) {e.printStackTrace();}}
}

CharArrayWriter：将字符写入字符数组

import java.io.CharArrayWriter;public class WriteCharArray {public static void main(String[] args) {String data = "Hello, World!";try (CharArrayWriter caw = new CharArrayWriter()) {caw.write(data);char[] output = caw.toCharArray();System.out.println(new String(output));}}
}

BufferedWriter：为其他字符输出流添加缓冲区

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;public class BufferedCharWrite {public static void main(String[] args) {String data = "Hello, World!\n";try (BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt", true))) {bw.write(data);bw.newLine(); // 写入换行符} catch (IOException e) {e.printStackTrace();}}
}

OutputStreamWriter：桥接器，将字符流转换为字节流

import java.io.OutputStreamWriter;
import java.io.FileOutputStream;
import java.io.IOException;public class CharToByte {public static void main(String[] args) {String data = "Hello, World!";try (OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("output.txt"), "UTF-8")) {osw.write(data);} catch (IOException e) {e.printStackTrace();}}
}

高级特性

Piped Streams：管道流使得一个线程可以通过管道将数据发送给另一个线程

import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.io.IOException;class Producer implements Runnable {private PipedOutputStream pos;Producer(PipedInputStream pis) throws IOException {pos = new PipedOutputStream(pis);}@Overridepublic void run() {try {String data = "Hello, Pipe!";pos.write(data.getBytes());pos.close();} catch (IOException e) {e.printStackTrace();}}
}class Consumer implements Runnable {private PipedInputStream pis;Consumer(PipedOutputStream pos) throws IOException {pis = new PipedInputStream(pos);}@Overridepublic void run() {try {int data;while ((data = pis.read()) != -1) {System.out.print((char) data);}pis.close();} catch (IOException e) {e.printStackTrace();}}
}public class PipeStreams {public static void main(String[] args) throws IOException {PipedInputStream pis = new PipedInputStream();PipedOutputStream pos = new PipedOutputStream(pis);Thread producerThread = new Thread(new Producer(pos));Thread consumerThread = new Thread(new Consumer(pis));producerThread.start();consumerThread.start();}
}

PrintStream：格式化输出流，通常用于标准输出（控制台）

import java.io.PrintStream;
import java.io.FileOutputStream;
import java.io.IOException;public class UsePrintStream {public static void main(String[] args) {try (PrintStream ps = new PrintStream(new FileOutputStream("output.txt"))) {ps.println("Hello, PrintStream!");ps.printf("This is a formatted string: %d%%\n", 100);} catch (IOException e) {e.printStackTrace();}}
}

Scanner：用于解析基础数据类型和字符串

import java.util.Scanner;
import java.io.File;
import java.io.IOException;public class UseScanner {public static void main(String[] args) {try (Scanner scanner = new Scanner(new File("input.txt"))) {while (scanner.hasNextLine()) {String line = scanner.nextLine();System.out.println(line);}} catch (IOException e) {e.printStackTrace();}}
}

Formatter：用于格式化输出

import java.io.PrintWriter;
import java.io.StringWriter;public class UseFormatter {public static void main(String[] args) {StringWriter sw = new StringWriter();PrintWriter pw = new PrintWriter(sw);pw.format("Hello, %s!\n", "Formatter");pw.format("Formatted integer: %d\n", 42);System.out.println(sw.toString());}
}

NIO (New IO)

Channels 和 Buffers

使用FileChannel和ByteBuffer读写文件

import java.nio.file.Paths;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.nio.channels.FileChannel;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.io.IOException;public class NIOExample {public static void main(String[] args) {Path path = Paths.get("output.txt");String data = "Hello NIO!";// Writing to file using FileChannel and ByteBuffertry (FileChannel channel = FileChannel.open(path, StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {ByteBuffer buffer = ByteBuffer.allocate(1024);buffer.put(data.getBytes(StandardCharsets.UTF_8));buffer.flip(); // Switch to read modechannel.write(buffer);} catch (IOException e) {e.printStackTrace();}// Reading from file using FileChannel and ByteBuffertry (FileChannel channel = FileChannel.open(path)) {ByteBuffer buffer = ByteBuffer.allocate(1024);int bytesRead = channel.read(buffer);buffer.flip(); // Switch to read modebyte[] bytes = new byte[bytesRead];buffer.get(bytes);System.out.println(new String(bytes, StandardCharsets.UTF_8));} catch (IOException e) {e.printStackTrace();}}
}

Selectors

选择器的使用稍微复杂一些，它主要用于网络编程中，以实现非阻塞I/O。这里提供一个简单的例子来展示如何创建和使用选择器监控多个SocketChannel。

import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.spi.SelectorProvider;public class SelectorExample {public static void main(String[] args) throws IOException {// Open a selectorSelector selector = SelectorProvider.provider().openSelector();// Open a server socket channel and bind it to port 8080ServerSocketChannel serverChannel = ServerSocketChannel.open();serverChannel.socket().bind(new InetSocketAddress(8080));serverChannel.configureBlocking(false);// Register the server channel with the selector for accepting connectionsserverChannel.register(selector, SelectionKey.OP_ACCEPT);// Loop indefinitely, waiting for events on the channels registered with the selectorwhile (true) {// Wait for at least one eventselector.select();// Get the set of keys with pending eventsfor (SelectionKey key : selector.selectedKeys()) {// Remove the current key from the set so it won't be processed againselector.selectedKeys().remove(key);if (!key.isValid()) {continue;}// Check what event is ready and handle itif (key.isAcceptable()) {// Accept the new connectionServerSocketChannel ssc = (ServerSocketChannel) key.channel();SocketChannel sc = ssc.accept();sc.configureBlocking(false);// Register the new SocketChannel with the selector for readingsc.register(selector, SelectionKey.OP_READ);} else if (key.isReadable()) {// Read the data from the clientSocketChannel sc = (SocketChannel) key.channel();// ... handle reading ...}}}}
}