我正在学习Java中的多线程，我的任务是使用2+线程复制文件。
文件扩展名无关紧要。所以我尝试在 2 个线程中完成。在第一个线程中，我复制文件的前半部分，在第二个线程中 - 第二个线程。我尝试将部分保存在字节数组中，然后转到主线程并使用 ByteArrayOutputStream 连接这些数组并保存源文件的副本。但它在三六次中工作一次两次。我不知道出了什么问题。如何使用 Java 在多个线程中复制文件
public class FirstThread implements Runnable {
private byte[] part1thread;
private RandomAccessFile file;
public FirstThread(RandomAccessFile file, int byteArraySize) {
this.file = file;
this.part1thread = new byte[byteArraySize];
}
public void run() {
try {
System.out.println("Start the first thread.");
file.read(part1thread, 0, part1thread.length);
System.out.println("I am the first thread and I read first part1thread of the file you gave me.");
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
RandomAccessFile fileOutputWrite = new RandomAccessFile("copy_", "rw");
System.out.println("First threads results writing...");
outputStream.write(this.part1thread);
System.out.println("output 1 thread: " + outputStream);
fileOutputWrite.write(this.getPart1thread(), 0, this.getPart1thread().length);
fileOutputWrite.close();
outputStream.close();
Main.setCountDownLatch();
} catch (IOException e) {
e.printStackTrace();
}
}
public byte[] getPart1thread() {
return part1thread;
}
}
public class SecondThread implements Runnable {
private byte[] part2thread;
private RandomAccessFile file;
private long tempBytesSize;
public SecondThread(RandomAccessFile file, int arrayFullSize) {
this.file = file;
tempBytesSize = arrayFullSize % 2 == 0 ? arrayFullSize/2 : arrayFullSize/2 + 1;
System.out.println(arrayFullSize % 2 == 0);
this.part2thread = new byte[(int)tempBytesSize];
}
public void run() {
try {
System.out.println("Start the second thread.");
file.seek(part2thread.length - 1);
System.out.println(tempBytesSize);
file.read(part2thread, 0, (int)tempBytesSize);
System.out.println("I am the second thread and I read second part2thread of the file you gave me.");
RandomAccessFile fileOutputWrite = new RandomAccessFile("copy_", "rw");
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
fileOutputWrite.seek(fileOutputWrite.length() - 1);
System.out.println("Second threads results writing..");
outputStream.write(this.getPart2thread());
System.out.println("output 2 thread: " + outputStream);
fileOutputWrite.write(this.getPart2thread(), 0, this.getPart2thread().length);
fileOutputWrite.close();
outputStream.close();
Main.setCountDownLatch();
} catch (IOException e) {
e.printStackTrace();
}
}
public byte[] getPart2thread() {
return part2thread;
}
}
public class Main {
private static volatile CountDownLatch countDownLatch;
public synchronized static void main(String[] args) throws IOException {
countDownLatch = new CountDownLatch(2);
Scanner scanner = new Scanner(System.in);
System.out.println("Enter file name with extension");
String fileName = scanner.nextLine();
RandomAccessFile file = null;
long partByteSize = 0;
try {
file = new RandomAccessFile(fileName, "r");
partByteSize = file.getChannel().size() / 2;
} catch (FileNotFoundException e) {
System.out.println("File not found!");
System.exit(-1);
} catch (IOException e) {
System.out.println("An error has been occured. Cannot work with file.");
System.exit(-1);
}
ExecutorService pool = Executors.newFixedThreadPool(2);
FirstThread firstThread = new FirstThread(file, (int) partByteSize);
SecondThread secondThread = new SecondThread(file, (int) file.getChannel().size());
pool.submit(firstThread);
pool.submit(secondThread);
try {
countDownLatch.await();
} catch (InterruptedException e) {
System.out.println("Unexpected error.");
System.exit(-1);
}
System.out.println("Return flow control to the main thread");
ByteArrayOutputStream outputStream;
file.close();
System.exit(0);
}
public static void setCountDownLatch() {
Main.countDownLatch.countDown();
}
}
我尝试使用*.pdf和*.txt文件。 *.pdf副本无法打开，*.txt文件：当我只复制前半部分或后半部分时，它运行良好。但是当我尝试一一复制两个部分时，它有时会起作用。我不知道如何解决它。
检查这个 60 行（内联注释）：
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
public class SOQ54295781 {
private static final int BUFF_SIZE = 4096;
public static void main(final String[] args) throws IOException {
// create a "piped stream":
final PipedOutputStream output = new PipedOutputStream();
final PipedInputStream input = new PipedInputStream(output);
//"read" thread:
Thread thread1 = new Thread(() -> {
System.out.println("t1 start...");
//opens source file ...
try (FileInputStream fileIn = new FileInputStream("test.pdf")) { //args[0]
// ... and copies to pipe.
long totalBytes = copy(fileIn, output, "t1", "from src file into pipe");
System.out.format("Reading from source file completed. Total: %d bytes.%n", totalBytes);
fileIn.close();
} catch (IOException e) {
e.printStackTrace(System.err);
} finally {
try {
output.close();
} catch (IOException ex) {
ex.printStackTrace(System.err);
}
}
System.out.println("t1 done.");
});
//"write" thread:
Thread thread2 = new Thread(() -> {
System.out.println("t2 start...");
// opens dest file ...
try (FileOutputStream fileOut = new FileOutputStream("test.copy.pdf")) {//args[1]
// ... and copies from pipe.
long totalBytes = copy(input, fileOut, "t2", "from pipe into dest file");
System.out.format("Writing to dest file completed. Total: %d bytes.%n", totalBytes);
fileOut.close();
} catch (IOException e) {
e.printStackTrace(System.err);
} finally {
try {
input.close();
} catch (IOException ex) {
ex.printStackTrace(System.err);
}
}
System.out.println("t2 done.");
});
thread1.start();
thread2.start();
}
// thx to https://stackoverflow.com/a/22128215/592355 resp. guava extended by some debug output
private static long copy(InputStream from, OutputStream to, String thread, String msg)
throws IOException {
byte[] buf = new byte[BUFF_SIZE];
long total = 0;
while (true) {
int r = from.read(buf);
if (r == -1) {
break;
}
to.write(buf, 0, r);
total += r;
System.out.format("I am %s, and I copied %d bytes %s.%n", thread, r, msg);
}
return total;
}
}
输出：
t2 start...
t1 start...
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t1, and I copied 4096 bytes from src file into pipe.
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t1, and I copied 4096 bytes from src file into pipe.
I am t2, and I copied 1024 bytes from pipe into dest file.
// ...
I am t2, and I copied 1024 bytes from pipe into dest file.
I am t1, and I copied 782 bytes from src file into pipe.
Reading from source file completed. Total: 6980366 bytes.
t1 done.
I am t2, and I copied 782 bytes from pipe into dest file.
Writing to dest file completed. Total: 6980366 bytes.
t2 done.
另请参阅：
- https://docs.oracle.com/javase/8/docs/api/java/io/PipedOutputStream.html
- https://docs.oracle.com/javase/8/docs/api/java/io/PipedInputStream.html
- 如何将一个流读入另一个流？
- http://tutorials.jenkov.com/java-io/pipes.html
我添加了方法
public boolean getState() {
return Thread.currentThread().isAlive();
}
进入 FirstThread 类
我把firstThread和secondThread作为Main类的成员。
if (Main.getFirstThread().getState()) {
我在第二线程的 run（） 方法中添加了 if 条件否则 - 我们递归地尝试再次运行方法 run（），直到第一个线程启动。
哈哈我需要
resultFile.seek(resultFile.length() - 0);
当我编写复制的文件时，cos 没有"- 0"它不起作用。