java分片读写文件

在Java中，对于大文件的读写，可以使用分片读写的方式来提高效率和降低内存消耗。以下是一个简单的分片读写文件的示例代码：

import java.io.*;

public class FileSplitter {
    private static final int BUFFER_SIZE = 1024 * 1024; // 每次读取的字节数

    public static void split(String inputPath, String outputPath, int chunkSize) throws IOException {
        File inputFile = new File(inputPath);
        long fileSize = inputFile.length();
        int numChunks = (int) Math.ceil((double) fileSize / chunkSize);

        try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(inputFile))) {
            byte[] buffer = new byte[BUFFER_SIZE];
            for (int i = 0; i < numChunks; i++) {
                int bytesRead = 0;
                int bytesToRead = chunkSize;
                if (i == numChunks - 1) {
                    // 最后一片可能不足chunkSize字节
                    bytesToRead = (int) (fileSize - i * chunkSize);
                }

                try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(outputPath + ".part" + i))) {
                    while (bytesRead < bytesToRead) {
                        int bytes = bis.read(buffer, 0, Math.min(BUFFER_SIZE, bytesToRead - bytesRead));
                        if (bytes < 0) {
                            break;
                        }
                        bytesRead += bytes;
                        bos.write(buffer, 0, bytes);
                    }
                }
            }
        }
    }

    public static void merge(String[] inputPaths, String outputPath) throws IOException {
        try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(outputPath))) {
            for (String inputPath : inputPaths) {
                try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(inputPath))) {
                    byte[] buffer = new byte[BUFFER_SIZE];
                    int bytesRead = 0;
                    while ((bytesRead = bis.read(buffer)) != -1) {
                        bos.write(buffer, 0, bytesRead);
                    }
                }
            }
        }
    }
}

其中，`split()`方法用于将一个大文件分成多个小文件，`merge()`方法用于将多个小文件合并成一个大文件。`chunkSize`参数指定每个小文件的大小，可以根据需要进行调整。在读取文件时，使用`BufferedInputStream`和`BufferedOutputStream`进行缓存，以提高效率。需要注意的是，在使用完输入输出流后，需要调用`close()`方法来关闭流，或使用`try-with-resources`语句来自动关闭流。