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FileInputStream fis = new FileInputStream(FILE_PATH);
FileChannel channel = fis.getChannel();FileOutputStream fos = new FileOutputStream(FILE_PATH);
FileChannel channel = fis.getChannel();RandomAccessFile raf = new RandomAccessFile(FILE_PATH , "rw");
FileChannel channel = raf.getChannel();

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// 获取管道
RandomAccessFile raf = new RandomAccessFile(FILE_PATH, "rw");
FileChannel rafChannel = raf.getChannel();// 准备数据
String data = "新数据，时间： " + System.currentTimeMillis();
System.out.println("原数据：\n" + "   " + data);
ByteBuffer buffer = ByteBuffer.allocate(128);
buffer.clear();
buffer.put(data.getBytes());
buffer.flip();// 写入数据
rafChannel.write(buffer);rafChannel.close();
raf.close();// 重新打开管道
raf = new RandomAccessFile(FILE_PATH, "rw");
rafChannel = raf.getChannel();// 读取刚刚写入的数据
buffer.clear();
rafChannel.read(buffer);// 打印读取出的数据
buffer.flip();
byte[] bytes = new byte[buffer.limit()];
buffer.get(bytes);
System.out.println("读取到的数据：\n" + "   " + new String(bytes));rafChannel.close();
raf.close();

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public static void main(String[] args) throws IOException {RandomAccessFile fromFile = new RandomAccessFile("fromFile.txt", "rw");FileChannel fromChannel = fromFile.getChannel();RandomAccessFile toFile = new RandomAccessFile("toFile.txt", "rw");FileChannel toChannel = toFile.getChannel();long position = 0;long count = fromChannel.size();// 将 fromFile 文件找那个的数据转移到 toFile 中去System.out.println("before transfer: " + readChannel(toChannel));fromChannel.transferTo(position, count, toChannel);System.out.println("after transfer : " + readChannel(toChannel));fromChannel.close();fromFile.close();toChannel.close();toFile.close();
}private static String readChannel(FileChannel channel) throws IOException {ByteBuffer buffer = ByteBuffer.allocate(32);buffer.clear();// 将 channel 读取位置设为 0，也就是文件开始位置channel.position(0);channel.read(buffer);// 再次将文件位置归零channel.position(0);buffer.flip();byte[] bytes = new byte[buffer.limit()];buffer.get(bytes);return new String(bytes);
}

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public long transferTo(long position, long count,WritableByteChannel target)throws IOException
{// 省略一些代码int icount = (int)Math.min(count, Integer.MAX_VALUE);if ((sz - position) < icount)icount = (int)(sz - position);long n;// Attempt a direct transfer, if the kernel supports itif ((n = transferToDirectly(position, icount, target)) >= 0)return n;// Attempt a mapped transfer, but only to trusted channel typesif ((n = transferToTrustedChannel(position, icount, target)) >= 0)return n;// Slow path for untrusted targetsreturn transferToArbitraryChannel(position, icount, target);
}private long transferToDirectly(long position, int icount,WritableByteChannel target)throws IOException
{// 省略一些代码long n = -1;int ti = -1;try {begin();ti = threads.add();if (!isOpen())return -1;do {n = transferTo0(thisFDVal, position, icount, targetFDVal);} while ((n == IOStatus.INTERRUPTED) && isOpen());// 省略一些代码return IOStatus.normalize(n);} finally {threads.remove(ti);end (n > -1);}
}

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JNIEXPORT jlong JNICALL
Java_sun_nio_ch_FileChannelImpl_transferTo0(JNIEnv *env, jobject this,jint srcFD,jlong position, jlong count,jint dstFD)
{
#if defined(__linux__)off64_t offset = (off64_t)position;jlong n = sendfile64(dstFD, srcFD, &offset, (size_t)count);if (n < 0) {if (errno == EAGAIN)return IOS_UNAVAILABLE;if ((errno == EINVAL) && ((ssize_t)count >= 0))return IOS_UNSUPPORTED_CASE;if (errno == EINTR) {return IOS_INTERRUPTED;}JNU_ThrowIOExceptionWithLastError(env, "Transfer failed");return IOS_THROWN;}return n;// 其他平台的代码省略
#endif
}

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// 从标准输入获取数据
Scanner sc = new Scanner(System.in);
System.out.println("请输入：");
String str = sc.nextLine();
byte[] bytes = str.getBytes();RandomAccessFile raf = new RandomAccessFile("map.txt", "rw");
FileChannel channel = raf.getChannel();// 获取内存映射缓冲区，并向缓冲区写入数据
MappedByteBuffer mappedBuffer = channel.map(MapMode.READ_WRITE, 0, bytes.length);
mappedBuffer.put(bytes);raf.close();
raf.close();// 再次打开刚刚的文件，读取其中的内容
raf = new RandomAccessFile("map.txt", "rw");
channel = raf.getChannel();
System.out.println("\n文件内容：")
System.out.println(readChannel(channel));raf.close();
raf.close();

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#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <memory.h>
#include <unistd.h>int main() {int dstfd;void *dst;char buf[64], out[64];int len;printf("Please input:\n");scanf("%s", buf);len = strlen(buf);// 打开文件dstfd = open("dst.txt", O_RDWR | O_CREAT | O_TRUNC, S_IRWXU);lseek(dstfd, len - 1, SEEK_SET);write(dstfd, "", 1);// 将文件映射到内存中dst = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, dstfd, 0);// 将输入的数据拷贝到映射内存中memcpy(dst, buf, len);munmap(dst, len);close(dstfd);// 重新打开文件，并输出文件内容dstfd = open("dst.txt", O_RDONLY);dst = mmap(NULL, len, PROT_READ, MAP_SHARED, dstfd, 0);bzero(out, 64);memcpy(out, dst, len);printf("\nfile content:\n%s\n", out);munmap(dst, len);close(dstfd);return 0;
}