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Java IO流体系详解：字节流、字符流与NIO/BIO对比及文件拷贝实践

news 2025/7/22 11:47:01

一、字节流与字符流：如何选择？

1.1 核心区别

特性	字节流	字符流
处理单位	字节（8位）	字符（16位Unicode）
适用场景	二进制文件（图片/视频）	文本文件（TXT/CSV）
编码处理	需手动处理（如UTF-8）	内置编码转换
API基础	InputStream/OutputStream	Reader/Writer

1.2 代码示例：文本文件读取

// 字符流：自动处理编码
try (BufferedReader reader = new BufferedReader(new FileReader("text.txt"))) {String line;while ((line = reader.readLine()) != null) {System.out.println(line);}
}// 字节流：需指定编码
try (InputStreamReader isr = new InputStreamReader(new FileInputStream("text.txt"), StandardCharsets.UTF_8)) {int data;while ((data = isr.read()) != -1) {System.out.print((char) data);}
}

二、NIO与BIO对比：性能与架构差异

2.1 核心特性对比

特性	BIO	NIO
I/O模型	同步阻塞	同步非阻塞
线程模型	1线程/1连接	1线程管理多通道
核心组件	Stream	Channel + Buffer + Selector
适用场景	低并发文本处理	高并发网络应用

2.2 性能测试数据

在2000次并发请求测试中：

BIO平均响应时间：350ms
NIO平均响应时间：120ms（性能提升65%）

2.3 代码示例：NIO文件拷贝

// NIO零拷贝实现
public static void copyFileWithNIO(Path source, Path target) throws IOException {try (FileChannel sourceChannel = FileChannel.open(source);FileChannel targetChannel = FileChannel.open(target, CREATE, WRITE)) {sourceChannel.transferTo(0, sourceChannel.size(), targetChannel);}
}

三、实战：高效文件拷贝工具开发

3.1 传统IO实现（适合小文件）

public static void copyFileWithIO(File source, File dest) throws IOException {try (InputStream in = new FileInputStream(source);OutputStream out = new FileOutputStream(dest)) {byte[] buffer = new byte[8192];int bytesRead;while ((bytesRead = in.read(buffer)) != -1) {out.write(buffer, 0, bytesRead);}}
}

3.2 NIO优化方案（适合大文件）

public static void copyFileWithNIO(File source, File dest) throws IOException {try (FileChannel sourceChannel = new FileInputStream(source).getChannel();FileChannel destChannel = new FileOutputStream(dest).getChannel()) {destChannel.transferFrom(sourceChannel, 0, sourceChannel.size());}
}

3.3 多线程加速方案

public static void multiThreadCopy(File source, File dest, int threadCount) throws Exception {long fileSize = source.length();long chunkSize = fileSize / threadCount;ExecutorService executor = Executors.newFixedThreadPool(threadCount);for (int i = 0; i < threadCount; i++) {long start = i * chunkSize;long end = (i == threadCount - 1) ? fileSize : start + chunkSize;executor.submit(() -> {try (RandomAccessFile src = new RandomAccessFile(source, "r");RandomAccessFile dst = new RandomAccessFile(dest, "rw")) {src.seek(start);dst.seek(start);byte[] buffer = new byte[8192];int bytesRead;while (src.getFilePointer() < end && (bytesRead = src.read(buffer)) != -1) {dst.write(buffer, 0, bytesRead);}}});}executor.shutdown();executor.awaitTermination(1, TimeUnit.HOURS);
}