java 文件分段读取 java分块读取文件

在开始处理块之前，您可以在文件中找到行边界处的偏移量。从偏移量开始，将文件大小除以块号，然后查找直到找到行边界。然后将这些偏移量输入到多线程文件处理器中。这是一个完整的示例，将可用处理器的数量用作块的数量：

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ReadFileByChunks {
public static void main(String[] args) throws IOException {
int chunks = Runtime.getRuntime().availableProcessors();
long[] offsets = new long[chunks];
File file = new File("your.file");
// determine line boundaries for number of chunks
RandomAccessFile raf = new RandomAccessFile(file, "r");
for (int i = 1; i < chunks; i++) {
raf.seek(i * file.length() / chunks);
while (true) {
int read = raf.read();
if (read == '\n' || read == -1) {
break;
}
}
offsets[i] = raf.getFilePointer();
}
raf.close();
// process each chunk using a thread for each one
ExecutorService service = Executors.newFixedThreadPool(chunks);
for (int i = 0; i < chunks; i++) {
long start = offsets[i];
long end = i < chunks - 1 ? offsets[i + 1] : file.length();
service.execute(new FileProcessor(file, start, end));
}
service.shutdown();
}
static class FileProcessor implements Runnable {
private final File file;
private final long start;
private final long end;
public FileProcessor(File file, long start, long end) {
this.file = file;
this.start = start;
this.end = end;
}
public void run() {
try {
RandomAccessFile raf = new RandomAccessFile(file, "r");
raf.seek(start);
while (raf.getFilePointer() < end) {
String line = raf.readLine();
if (line == null) {
continue;
}
// do what you need per line here
System.out.println(line);
}
raf.close();
} catch (IOException e) {
// deal with exception
}
}
}
}