Java IO流：输入输出的艺术

概述

Java IO流是处理输入输出的机制，它通过流的概念来读写数据。Java提供了丰富的IO类库，包括字节流、字符流、缓冲流等。

1. 字节流

import java.io.*;

// 文件复制
public class FileCopy {
    public static void copyFile(String src, String dest) throws IOException {
        try (FileInputStream fis = new FileInputStream(src);
             FileOutputStream fos = new FileOutputStream(dest)) {
            byte[] buffer = new byte[1024];
            int length;
            while ((length = fis.read(buffer)) != -1) {
                fos.write(buffer, 0, length);
            }
        }
    }
}

2. 字符流

public class CharStreamDemo {
    public static void writeToFile(String filename, String content) throws IOException {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(filename))) {
            writer.write(content);
        }
    }

    public static String readFromFile(String filename) throws IOException {
        StringBuilder content = new StringBuilder();
        try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
            String line;
            while ((line = reader.readLine()) != null) {
                content.append(line).append("\n");
            }
        }
        return content.toString();
    }
}

3. 缓冲流

public class BufferedStreamDemo {
    public static void processLargeFile(String filename) throws IOException {
        try (BufferedReader reader = new BufferedReader(
                new InputStreamReader(new FileInputStream(filename)))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        }
    }
}

4. 对象序列化

public class User implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private int age;
    private transient String password;
}

public class SerializationDemo {
    public static void serialize(Object obj, String filename) throws IOException {
        try (ObjectOutputStream oos = new ObjectOutputStream(
                new FileOutputStream(filename))) {
            oos.writeObject(obj);
        }
    }

    public static Object deserialize(String filename)
            throws IOException, ClassNotFoundException {
        try (ObjectInputStream ois = new ObjectInputStream(
                new FileInputStream(filename))) {
            return ois.readObject();
        }
    }
}

5. File类操作

import java.io.File;

public class FileOperationDemo {
    public static void main(String[] args) {
        File dir = new File("testDir");
        dir.mkdir();

        File file = new File(dir, "test.txt");
        try {
            file.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }

        System.out.println("文件名: " + file.getName());
        System.out.println("绝对路径: " + file.getAbsolutePath());
        System.out.println("文件大小: " + file.length() + " bytes");
        System.out.println("是否文件: " + file.isFile());
        System.out.println("是否目录: " + file.isDirectory());
    }
}

6. NIO简介

import java.nio.*;
import java.nio.file.*;

public class NIODemo {
    public static void main(String[] args) throws IOException {
        Path path = Paths.get("/home/user/file.txt");
        System.out.println("文件名: " + path.getFileName());
        System.out.println("绝对路径: " + path.toAbsolutePath());

        List<String> lines = Files.readAllLines(path);
        Files.write(path, lines);
        Files.copy(path, Paths.get("/home/user/backup.txt"));
        Files.deleteIfExists(path);
    }
}

最佳实践

1. 使用try-with-resources：自动关闭流资源
2. 使用缓冲流：提高IO性能
3. 使用NIO：处理大文件和非阻塞IO
4. 异常处理：捕获和处理IOException
5. 字符编码：指定正确的字符编码

总结

Java IO流是处理输入输出的基础，掌握字节流、字符流、缓冲流和NIO的使用，可以高效地进行文件操作和数据传输。合理选择IO方式，是编写高效Java程序的关键。