Java IO流与NIO技术综合应用

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);
    }

    @Override
    public 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);
    }

    @Override
    public 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 ByteBuffer
        try (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 mode
            channel.write(buffer);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Reading from file using FileChannel and ByteBuffer
        try (FileChannel channel = FileChannel.open(path)) {
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            int bytesRead = channel.read(buffer);
            buffer.flip(); // Switch to read mode
            byte[] 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 selector
        Selector selector = SelectorProvider.provider().openSelector();

        // Open a server socket channel and bind it to port 8080
        ServerSocketChannel serverChannel = ServerSocketChannel.open();
        serverChannel.socket().bind(new InetSocketAddress(8080));
        serverChannel.configureBlocking(false);

        // Register the server channel with the selector for accepting connections
        serverChannel.register(selector, SelectionKey.OP_ACCEPT);

        // Loop indefinitely, waiting for events on the channels registered with the selector
        while (true) {
            // Wait for at least one event
            selector.select();

            // Get the set of keys with pending events
            for (SelectionKey key : selector.selectedKeys()) {
                // Remove the current key from the set so it won't be processed again
                selector.selectedKeys().remove(key);

                if (!key.isValid()) {
                    continue;
                }

                // Check what event is ready and handle it
                if (key.isAcceptable()) {
                    // Accept the new connection
                    ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                    SocketChannel sc = ssc.accept();
                    sc.configureBlocking(false);
                    // Register the new SocketChannel with the selector for reading
                    sc.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    // Read the data from the client
                    SocketChannel sc = (SocketChannel) key.channel();
                    // ... handle reading ...
                }
            }
        }
    }
}