Java : SeekableByteChannel 示例

Java 中的 SeekableByteChannel (Java SE 24 & JDK 24) 及其示例。
您将找到大多数 SeekableByteChannel 方法的代码示例。

注解 :

本文可能使用了翻译软件以方便阅读。另请查看英文原文。

简介

维护当前位置并允许改变位置的字节通道。 (机器翻译)

Class diagram

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

final byte[] bytes = {10, 20, 30, 40, 50};
Files.write(path, bytes);

try (final SeekableByteChannel channel =
             Files.newByteChannel(path, StandardOpenOption.READ)) {

    channel.position(2);

    {
        System.out.println(channel.position()); // 2

        final var buffer = ByteBuffer.allocate(3);
        final var ret = channel.read(buffer);
        System.out.println(ret); // 3

        System.out.println(channel.position()); // 5

        if (buffer.hasArray()) {
            // [30, 40, 50]
            System.out.println(Arrays.toString(buffer.array()));
        }
    }

    channel.position(0);

    {
        System.out.println(channel.position()); // 0

        final var buffer = ByteBuffer.allocate(5);
        final var ret = channel.read(buffer);
        System.out.println(ret); // 5

        System.out.println(channel.position()); // 5

        if (buffer.hasArray()) {
            // [10, 20, 30, 40, 50]
            System.out.println(Arrays.toString(buffer.array()));
        }
    }
}

Methods

long position ()

返回此频道的位置。 (机器翻译)

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

final byte[] bytes = {10, 20, 30, 40, 50};
Files.write(path, bytes);

try (final SeekableByteChannel channel =
             Files.newByteChannel(path, StandardOpenOption.READ)) {

    final var ret1 = channel.position(2);
    System.out.println(channel.equals(ret1)); // true

    {
        System.out.println(channel.position()); // 2

        final var buffer = ByteBuffer.allocate(3);
        final var ret = channel.read(buffer);
        System.out.println(ret); // 3

        System.out.println(channel.position()); // 5

        if (buffer.hasArray()) {
            // [30, 40, 50]
            System.out.println(Arrays.toString(buffer.array()));
        }
    }

    final var ret2 = channel.position(0);
    System.out.println(channel.equals(ret2)); // true

    {
        System.out.println(channel.position()); // 0

        final var buffer = ByteBuffer.allocate(5);
        final var ret = channel.read(buffer);
        System.out.println(ret); // 5

        System.out.println(channel.position()); // 5

        if (buffer.hasArray()) {
            // [10, 20, 30, 40, 50]
            System.out.println(Arrays.toString(buffer.array()));
        }
    }
}

SeekableByteChannel position (long newPosition)

设置该频道的位置。 (机器翻译)

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

final byte[] bytes = {10, 20, 30, 40, 50};
Files.write(path, bytes);

try (final SeekableByteChannel channel =
             Files.newByteChannel(path, StandardOpenOption.READ)) {

    final var ret1 = channel.position(2);
    System.out.println(channel.equals(ret1)); // true

    {
        System.out.println(channel.position()); // 2

        final var buffer = ByteBuffer.allocate(3);
        final var ret = channel.read(buffer);
        System.out.println(ret); // 3

        System.out.println(channel.position()); // 5

        if (buffer.hasArray()) {
            // [30, 40, 50]
            System.out.println(Arrays.toString(buffer.array()));
        }
    }

    final var ret2 = channel.position(0);
    System.out.println(channel.equals(ret2)); // true

    {
        System.out.println(channel.position()); // 0

        final var buffer = ByteBuffer.allocate(5);
        final var ret = channel.read(buffer);
        System.out.println(ret); // 5

        System.out.println(channel.position()); // 5

        if (buffer.hasArray()) {
            // [10, 20, 30, 40, 50]
            System.out.println(Arrays.toString(buffer.array()));
        }
    }
}

int read (ByteBuffer dst)

将字节序列从该通道读取到给定的缓冲区。 (机器翻译)

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

final byte[] bytes = {10, 20, 30};
Files.write(path, bytes);

try (final SeekableByteChannel channel =
             Files.newByteChannel(path, StandardOpenOption.READ)) {

    final var array = new byte[5];
    final var dst = ByteBuffer.wrap(array);

    System.out.println(dst); // java.nio.HeapByteBuffer[pos=0 lim=5 cap=5]
    System.out.println(Arrays.toString(array)); // [0, 0, 0, 0, 0]

    System.out.println(channel.position()); // 0

    final var ret = channel.read(dst);
    System.out.println(ret); // 3

    System.out.println(channel.position()); // 3

    System.out.println(dst); // java.nio.HeapByteBuffer[pos=3 lim=5 cap=5]
    System.out.println(Arrays.toString(array)); // [10, 20, 30, 0, 0]
}

long size ()

返回此通道所连接的实体的当前大小。 (机器翻译)

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

final byte[] bytes = {10, 20, 30, 40, 50};
Files.write(path, bytes);

try (final SeekableByteChannel channel =
             Files.newByteChannel(path, StandardOpenOption.READ)) {

    final var size = channel.size();
    System.out.println(size); // 5

    final var dst = ByteBuffer.allocate(Math.toIntExact(size));
    System.out.println(channel.read(dst)); // 5

    if (dst.hasArray()) {
        // [10, 20, 30, 40, 50]
        System.out.println(Arrays.toString(dst.array()));
    }
}

SeekableByteChannel truncate (long size)

将此通道所连接的实体截断为给定的大小。 (机器翻译)

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

final byte[] bytes = {10, 20, 30, 40, 50};
Files.write(path, bytes);

try (final SeekableByteChannel channel =
             Files.newByteChannel(path, StandardOpenOption.WRITE)) {

    final var ret = channel.truncate(3);
    System.out.println(channel.equals(ret)); // true

    final var size = channel.size();
    System.out.println(size); // 3
}

// [10, 20, 30]
System.out.println(Arrays.toString(Files.readAllBytes(path)));

int write (ByteBuffer src)

从给定的缓冲区将字节序列写入该通道。 (机器翻译)

final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data

try (final SeekableByteChannel channel = Files.newByteChannel(path,
        StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {

    final byte[] array = {10, 20, 30, 40, 50};
    final var src = ByteBuffer.wrap(array);

    src.limit(3);

    System.out.println(src); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=5]
    System.out.println(channel.position()); // 0

    final var ret = channel.write(src);
    System.out.println(ret); // 3

    System.out.println(src); // java.nio.HeapByteBuffer[pos=3 lim=3 cap=5]
    System.out.println(channel.position()); // 3
}

final var bytes = Files.readAllBytes(path);
System.out.println(Arrays.toString(bytes)); // [10, 20, 30]

Methods declared in Channel

close, isOpen

请参阅下面的链接。

Channel 示例

API 示例
- Channel
- ClosedChannelException
  - AsynchronousCloseException
  - ClosedByInterruptException

Java : SeekableByteChannel 示例

简介

Methods

long position ()

SeekableByteChannel position (long newPosition)

int read (ByteBuffer dst)

long size ()

SeekableByteChannel truncate (long size)

int write (ByteBuffer src)

Methods declared in Channel

close, isOpen

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