Java : FileChannel con ejemplos
FileChannel (Java SE 22 & JDK 22) en Java con ejemplos.
Encontrará muestras de código para la mayoría de los métodos FileChannel.
Nota :
- Este artículo puede utilizar software de traducción para su comodidad. Consulte también la versión original en inglés.
Summary
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final var src = ByteBuffer.allocate(5)
.put((byte) 10)
.put((byte) 20)
.put((byte) 30)
.put((byte) 40)
.put((byte) 50)
.clear();
final var ret = channel.write(src);
System.out.println(ret); // 5
}
try (final var channel = FileChannel.open(path, StandardOpenOption.READ)) {
final var dst = ByteBuffer.allocate(5);
final var ret = channel.read(dst);
System.out.println(ret); // 5
if (dst.hasArray()) {
// [10, 20, 30, 40, 50]
System.out.println(Arrays.toString(dst.array()));
}
}
Constructors
FileChannel ()
protected. I think it's rare to create a subclass of this class. Therefore, the code example is omitted.
Methods
abstract void force (boolean metaData)
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
System.out.println(Files.notExists(path)); // true
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final byte[] array = {10, 20, 30, 40, 50};
final var src = ByteBuffer.wrap(array);
// --- PowerShell ---
//PS R:\java-work> ls | Format-Table -Property Length, Name
//
//Length Name
//------ ----
// 0 test.data
System.out.println(channel.write(src)); // 5
System.out.println(channel.size()); // 5
// --- PowerShell ---
//PS R:\java-work> ls | Format-Table -Property Length, Name
//
//Length Name
//------ ----
// 0 test.data
channel.force(true);
// --- PowerShell ---
//PS R:\java-work> ls | Format-Table -Property Length, Name
//
//Length Name
//------ ----
// 5 test.data
}
final FileLock lock ()
Please see also : FileLock
public class Child {
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 1) {
throw new IllegalArgumentException();
}
final var name = "child " + args[0];
final var file = Path.of("lock.txt");
try (final var channel = FileChannel.open(
file, StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
System.out.printf(" %s : lock start ...%n", name);
try (final var lock = channel.lock()) {
TimeUnit.MILLISECONDS.sleep(100);
System.out.printf(" %s : *** lock OK! ***%n", name);
System.out.printf(" %s : sleep 5 seconds ...%n", name);
TimeUnit.SECONDS.sleep(5);
System.out.printf(" %s : sleep end%n", name);
}
System.out.printf(" %s : lock end%n", name);
}
}
}
public class Main {
public static void main(String[] args) throws IOException, InterruptedException {
System.out.println("main : start");
final var p1 = new ProcessBuilder("java", "Child", "1").inheritIO().start();
TimeUnit.MILLISECONDS.sleep(10);
final var p2 = new ProcessBuilder("java", "Child", "2").inheritIO().start();
p1.waitFor();
p2.waitFor();
System.out.println("main : end");
}
}
// Result
// ↓
//> java Main
//main : start
// child 1 : lock start ...
// child 2 : lock start ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 2 : sleep end
// child 2 : lock end
//main : end
abstract FileLock lock (long position, long size, boolean shared)
An example for position and size parameters.
public class Child {
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 3) {
throw new IllegalArgumentException();
}
final var name = "child " + args[0];
final var position = Long.parseLong(args[1]);
final var size = Long.parseLong(args[2]);
final var file = Path.of("lock.txt");
try (final var channel = FileChannel.open(
file, StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
System.out.printf(" %s : lock start (position=%d, size=%d) ...%n",
name, position, size);
try (final var lock = channel.lock(position, size, false)) {
TimeUnit.MILLISECONDS.sleep(100);
System.out.printf(" %s : *** lock OK! ***%n", name);
System.out.printf(" %s : sleep 5 seconds ...%n", name);
TimeUnit.SECONDS.sleep(5);
System.out.printf(" %s : sleep end%n", name);
}
System.out.printf(" %s : lock end%n", name);
}
}
}
public class Main {
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 2) {
throw new IllegalArgumentException();
}
System.out.println("main : start");
final var p1 = new ProcessBuilder("java", "Child", "1", "0", "10").inheritIO().start();
TimeUnit.MILLISECONDS.sleep(10);
final var p2 = new ProcessBuilder("java", "Child", "2", args[0], args[1]).inheritIO().start();
p1.waitFor();
p2.waitFor();
System.out.println("main : end");
}
}
// Result
// ↓
//> java Main 0 10
//main : start
// child 1 : lock start (position=0, size=10) ...
// child 2 : lock start (position=0, size=10) ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 2 : sleep end
// child 2 : lock end
//main : end
//
//> java Main 11 5
//main : start
// child 1 : lock start (position=0, size=10) ...
// child 2 : lock start (position=11, size=5) ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : sleep end
// child 2 : lock end
//main : end
An example for the shared parameter.
public class Child {
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 2) {
throw new IllegalArgumentException();
}
final var name = "child " + args[0];
final var shared = "shared".equals(args[1]);
final var file = Path.of("lock.txt");
try (final var channel = FileChannel.open(file, StandardOpenOption.CREATE,
StandardOpenOption.WRITE, StandardOpenOption.READ)) {
System.out.printf(" %s : lock start (shared=%b) ...%n", name, shared);
try (final var lock = channel.lock(0, Long.MAX_VALUE, shared)) {
TimeUnit.MILLISECONDS.sleep(100);
System.out.printf(" %s : *** lock OK! ***%n", name);
System.out.printf(" %s : sleep 5 seconds ...%n", name);
TimeUnit.SECONDS.sleep(5);
System.out.printf(" %s : sleep end%n", name);
}
System.out.printf(" %s : lock end%n", name);
}
}
}
public class Main {
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 2) {
throw new IllegalArgumentException();
}
System.out.println("main : start");
final var p1 = new ProcessBuilder("java", "Child", "1", args[0]).inheritIO().start();
TimeUnit.MILLISECONDS.sleep(10);
final var p2 = new ProcessBuilder("java", "Child", "2", args[1]).inheritIO().start();
p1.waitFor();
p2.waitFor();
System.out.println("main : end");
}
}
// Result
// ↓
//> java Main shared shared
//main : start
// child 1 : lock start (shared=true) ...
// child 2 : lock start (shared=true) ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : sleep end
// child 2 : lock end
//main : end
//
//> java Main shared exclusive
//main : start
// child 1 : lock start (shared=true) ...
// child 2 : lock start (shared=false) ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 2 : sleep end
// child 2 : lock end
//main : end
//
//> java Main exclusive shared
//main : start
// child 1 : lock start (shared=false) ...
// child 2 : lock start (shared=true) ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 2 : sleep end
// child 2 : lock end
//main : end
//
//> java Main exclusive exclusive
//main : start
// child 1 : lock start (shared=false) ...
// child 2 : lock start (shared=false) ...
// child 1 : *** lock OK! ***
// child 1 : sleep 5 seconds ...
// child 1 : sleep end
// child 1 : lock end
// child 2 : *** lock OK! ***
// child 2 : sleep 5 seconds ...
// child 2 : sleep end
// child 2 : lock end
//main : end
abstract MappedByteBuffer map (FileChannel.MapMode mode, long position, long size)
Please see also : MappedByteBuffer
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 var channel = FileChannel.open(path,
StandardOpenOption.READ, StandardOpenOption.WRITE)) {
final var buffer = channel.map(
FileChannel.MapMode.READ_WRITE, 0, channel.size());
{
final var dst = new byte[buffer.capacity()];
buffer.get(0, dst);
System.out.println(Arrays.toString(dst)); // [10, 20, 30, 40, 50]
final var ret = Files.readAllBytes(path);
System.out.println(Arrays.toString(ret)); // [10, 20, 30, 40, 50]
}
buffer.put(0, (byte) -10);
buffer.put(1, (byte) -20);
buffer.put(2, (byte) -30);
{
final var dst = new byte[buffer.capacity()];
buffer.get(0, dst);
System.out.println(Arrays.toString(dst)); // [-10, -20, -30, 40, 50]
final var ret = Files.readAllBytes(path);
System.out.println(Arrays.toString(ret)); // [-10, -20, -30, 40, 50]
}
}
MemorySegment map (FileChannel.MapMode mode, long offset, long size, Arena arena)
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 var channel = FileChannel.open(path,
StandardOpenOption.READ, StandardOpenOption.WRITE)) {
final var segment = channel.map(
FileChannel.MapMode.READ_WRITE, 0, channel.size(), Arena.ofAuto());
{
final var dst = segment.toArray(ValueLayout.JAVA_BYTE);
System.out.println(Arrays.toString(dst)); // [10, 20, 30, 40, 50]
final var ret = Files.readAllBytes(path);
System.out.println(Arrays.toString(ret)); // [10, 20, 30, 40, 50]
}
segment.set(ValueLayout.JAVA_BYTE, 0, (byte) -10);
segment.set(ValueLayout.JAVA_BYTE, 1, (byte) -20);
segment.set(ValueLayout.JAVA_BYTE, 2, (byte) -30);
{
final var dst = segment.toArray(ValueLayout.JAVA_BYTE);
System.out.println(Arrays.toString(dst)); // [-10, -20, -30, 40, 50]
final var ret = Files.readAllBytes(path);
System.out.println(Arrays.toString(ret)); // [-10, -20, -30, 40, 50]
}
}
static FileChannel open (Path path, OpenOption... options)
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final var src = ByteBuffer.allocate(5)
.put((byte) 10)
.put((byte) 20)
.put((byte) 30)
.put((byte) 40)
.put((byte) 50)
.clear();
final var ret = channel.write(src);
System.out.println(ret); // 5
}
try (final var channel = FileChannel.open(path, StandardOpenOption.READ)) {
final var dst = ByteBuffer.allocate(5);
final var ret = channel.read(dst);
System.out.println(ret); // 5
if (dst.hasArray()) {
// [10, 20, 30, 40, 50]
System.out.println(Arrays.toString(dst.array()));
}
}
static FileChannel open (Path path, Set<? extends OpenOption> options, FileAttribute<?>... attrs)
Please see also open(Path path, OpenOption... options) for parameters other than the attrs parameter.
The following code runs on Linux.
public class Main {
public static void main(String[] args) throws IOException {
System.out.println(System.getProperty("os.name")); // Linux
{
final var file = Path.of("sample1.txt");
try (final var _ = FileChannel.open(file,
Set.of(StandardOpenOption.CREATE, StandardOpenOption.WRITE))) {
}
// --- Linux Terminal ---
//$ ls -l sample1.txt
//-rw-rw-r-- 1 xxxx xxxx 0 ... sample1.txt
}
{
final var permissions = PosixFilePermissions.fromString("rw-r-----");
final var attrs = PosixFilePermissions.asFileAttribute(permissions);
final var file = Path.of("sample2.txt");
try (final var _ = FileChannel.open(file,
Set.of(StandardOpenOption.CREATE, StandardOpenOption.WRITE),
attrs)) {
}
// --- Linux Terminal ---
//$ ls -l sample2.txt
//-rw-r----- 1 xxxx xxxx 0 ... sample2.txt
}
}
}
abstract long position ()
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 var channel = FileChannel.open(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()));
}
}
}
abstract FileChannel position (long newPosition)
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 var channel = FileChannel.open(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()));
}
}
}
abstract int read (ByteBuffer dst)
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 var channel = FileChannel.open(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]
}
final long read (ByteBuffer[] dsts)
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, 60, 70, 80, 90};
Files.write(path, bytes);
try (final var channel = FileChannel.open(path, StandardOpenOption.READ)) {
final ByteBuffer[] dsts = {
ByteBuffer.allocate(2),
ByteBuffer.allocate(3),
ByteBuffer.allocate(4),
};
final var ret = channel.read(dsts);
System.out.println(ret); // 9
System.out.println("-- dsts --");
for (final var dst : dsts) {
if (dst.hasArray()) {
System.out.println(Arrays.toString(dst.array()));
}
}
// Result
// ↓
//-- dsts --
//[10, 20]
//[30, 40, 50]
//[60, 70, 80, 90]
}
abstract long read (ByteBuffer[] dsts, int offset, int length)
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, 60, 70, 80, 90};
Files.write(path, bytes);
try (final var channel = FileChannel.open(path, StandardOpenOption.READ)) {
final ByteBuffer[] dsts = {
ByteBuffer.allocate(1),
ByteBuffer.allocate(2),
ByteBuffer.allocate(3),
ByteBuffer.allocate(4),
ByteBuffer.allocate(5),
};
final var ret = channel.read(dsts, 1, 3);
System.out.println(ret); // 9
System.out.println("-- dsts --");
for (final var dst : dsts) {
if (dst.hasArray()) {
System.out.println(Arrays.toString(dst.array()));
}
}
// Result
// ↓
//-- dsts --
//[0]
//[10, 20]
//[30, 40, 50]
//[60, 70, 80, 90]
//[0, 0, 0, 0, 0]
}
abstract int read (ByteBuffer dst, long position)
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 var channel = FileChannel.open(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, 2);
System.out.println(ret); // 3
System.out.println(channel.position()); // 0
System.out.println(dst); // java.nio.HeapByteBuffer[pos=3 lim=5 cap=5]
System.out.println(Arrays.toString(array)); // [30, 40, 50, 0, 0]
}
abstract long size ()
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 var channel = FileChannel.open(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()));
}
}
abstract long transferFrom (ReadableByteChannel src, long position, long count)
final var srcPath = Path.of("R:", "java-work", "src.data");
System.out.println(srcPath); // R:\java-work\src.data
final var dstPath = Path.of("R:", "java-work", "dst.data");
System.out.println(dstPath); // R:\java-work\dst.data
Files.write(srcPath, new byte[]{10, 20, 30});
try (final var channel = FileChannel.open(dstPath,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
System.out.println(channel.size()); // 0
try (final var src = FileChannel.open(srcPath, StandardOpenOption.READ)) {
final var ret = channel.transferFrom(src, 0, src.size());
System.out.println(ret); // 3
}
}
final var bytes = Files.readAllBytes(dstPath);
System.out.println(Arrays.toString(bytes)); // [10, 20, 30]
final var srcPath = Path.of("R:", "java-work", "src.data");
System.out.println(srcPath); // R:\java-work\src.data
final var dstPath = Path.of("R:", "java-work", "dst.data");
System.out.println(dstPath); // R:\java-work\dst.data
Files.write(srcPath, new byte[]{10, 20, 30});
Files.write(dstPath, new byte[]{-1, -2, -3, -4, -5, -6, -7});
try (final var channel = FileChannel.open(dstPath,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
System.out.println(channel.size()); // 7
try (final var src = FileChannel.open(srcPath, StandardOpenOption.READ)) {
final var ret = channel.transferFrom(src, 2, 3);
System.out.println(ret); // 3
}
}
final var bytes = Files.readAllBytes(dstPath);
System.out.println(Arrays.toString(bytes)); // [-1, -2, 10, 20, 30, -6, -7]
abstract long transferTo (long position, long count, WritableByteChannel target)
final var srcPath = Path.of("R:", "java-work", "src.data");
System.out.println(srcPath); // R:\java-work\src.data
final var dstPath = Path.of("R:", "java-work", "dst.data");
System.out.println(dstPath); // R:\java-work\dst.data
Files.write(srcPath, new byte[]{10, 20, 30});
try (final var channel = FileChannel.open(srcPath, StandardOpenOption.READ)) {
System.out.println(channel.size()); // 3
try (final var target = FileChannel.open(dstPath,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final var ret = channel.transferTo(0, channel.size(), target);
System.out.println(ret); // 3
}
}
final var bytes = Files.readAllBytes(dstPath);
System.out.println(Arrays.toString(bytes)); // [10, 20, 30]
final var srcFile = Path.of("R:", "java-work", "src.data");
System.out.println(srcFile); // R:\java-work\src.data
final var dstFile = Path.of("R:", "java-work", "dst.data");
System.out.println(dstFile); // R:\java-work\dst.data
Files.write(srcFile, new byte[]{10, 20, 30, 40, 50, 60, 70});
try (final var channel = FileChannel.open(srcFile, StandardOpenOption.READ)) {
System.out.println(channel.size()); // 7
try (final var target = FileChannel.open(dstFile,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final var ret = channel.transferTo(2, 3, target);
System.out.println(ret); // 3
}
}
final var bytes = Files.readAllBytes(dstFile);
System.out.println(Arrays.toString(bytes)); // [30, 40, 50]
abstract FileChannel truncate (long size)
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 var channel = FileChannel.open(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)));
final FileLock tryLock ()
Please see also : FileLock
public class Child {
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 1) {
throw new IllegalArgumentException();
}
final var name = "child " + args[0];
final var file = Path.of("lock.txt");
try (final var channel = FileChannel.open(
file, StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
System.out.printf(" %s : lock start ...%n", name);
while (true) {
try (final var lock = channel.tryLock()) {
TimeUnit.MILLISECONDS.sleep(100);
if (lock != null) {
System.out.printf(" %s : *** lock OK! ***%n", name);
System.out.printf(" %s : sleep 3 seconds ...%n", name);
TimeUnit.SECONDS.sleep(3);
break;
} else {
System.out.printf(" %s : ### lock NG! ###%n", name);
System.out.printf(" %s : sleep 1 second ...%n", name);
TimeUnit.SECONDS.sleep(1);
}
}
}
System.out.printf(" %s : lock end%n", name);
}
}
}
public class Main {
public static void main(String[] args) throws IOException, InterruptedException {
System.out.println("main : start");
final var p1 = new ProcessBuilder("java", "Child", "1").inheritIO().start();
TimeUnit.MILLISECONDS.sleep(10);
final var p2 = new ProcessBuilder("java", "Child", "2").inheritIO().start();
p1.waitFor();
p2.waitFor();
System.out.println("main : end");
}
}
// Result
// ↓
//> java Main
//main : start
// child 1 : lock start ...
// child 2 : lock start ...
// child 1 : *** lock OK! ***
// child 1 : sleep 3 seconds ...
// child 2 : ### lock NG! ###
// child 2 : sleep 1 second ...
// child 2 : ### lock NG! ###
// child 2 : sleep 1 second ...
// child 2 : ### lock NG! ###
// child 2 : sleep 1 second ...
// child 1 : lock end
// child 2 : *** lock OK! ***
// child 2 : sleep 3 seconds ...
// child 2 : lock end
//main : end
abstract FileLock tryLock (long position, long size, boolean shared)
Please see :
- tryLock() for the basic behavior of this method.
- lock(long position, long size, boolean shared) for position, size and shared parameters.
abstract int write (ByteBuffer src)
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final byte[] array = {10, 20, 30, 40, 50};
final var src = ByteBuffer.wrap(array);
System.out.println(src); // java.nio.HeapByteBuffer[pos=0 lim=5 cap=5]
System.out.println(channel.position()); // 0
final var ret = channel.write(src);
System.out.println(ret); // 5
System.out.println(src); // java.nio.HeapByteBuffer[pos=5 lim=5 cap=5]
System.out.println(channel.position()); // 5
}
final var bytes = Files.readAllBytes(path);
System.out.println(Arrays.toString(bytes)); // [10, 20, 30, 40, 50]
final long write (ByteBuffer[] srcs)
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final ByteBuffer[] srcs = {
ByteBuffer.wrap(new byte[]{10, 20}),
ByteBuffer.wrap(new byte[]{30, 40, 50}),
ByteBuffer.wrap(new byte[]{60, 70, 80, 90}),
};
final var ret = channel.write(srcs);
System.out.println(ret); // 9
}
final var bytes = Files.readAllBytes(path);
// [10, 20, 30, 40, 50, 60, 70, 80, 90]
System.out.println(Arrays.toString(bytes));
abstract long write (ByteBuffer[] srcs, int offset, int length)
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final ByteBuffer[] srcs = {
ByteBuffer.wrap(new byte[]{10}),
ByteBuffer.wrap(new byte[]{20, 30}),
ByteBuffer.wrap(new byte[]{40, 50, 60}),
ByteBuffer.wrap(new byte[]{70, 80, 90, 100}),
};
final var ret = channel.write(srcs, 1, 2);
System.out.println(ret); // 5
}
final var bytes = Files.readAllBytes(path);
// [20, 30, 40, 50, 60]
System.out.println(Arrays.toString(bytes));
abstract int write (ByteBuffer src, long position)
final var path = Path.of("R:", "java-work", "test.data");
System.out.println(path); // R:\java-work\test.data
Files.write(path, new byte[]{-1, -2, -3, -4, -5, -6, -7});
try (final var channel = FileChannel.open(path,
StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
final byte[] array = {10, 20, 30};
final var src = ByteBuffer.wrap(array);
System.out.println(src); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=3]
System.out.println(channel.position()); // 0
final var ret = channel.write(src, 2);
System.out.println(ret); // 3
System.out.println(src); // java.nio.HeapByteBuffer[pos=3 lim=3 cap=3]
System.out.println(channel.position()); // 0
}
final var bytes = Files.readAllBytes(path);
System.out.println(Arrays.toString(bytes)); // [-1, -2, 10, 20, 30, -6, -7]
Methods declared in AbstractInterruptibleChannel
begin, close, end, implCloseChannel, isOpen
Consulte el siguiente enlace.
Methods declared in Channel
Related posts
- Ejemplos de API