How do I close the MappedByteBuffer correctly?
This is the code I am running:
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
public static void main(String[] args) throws Exception {
String filePath = "D:/temp/file";
RandomAccessFile file = new RandomAccessFile(filePath, "rw");
try {
MappedByteBuffer buffer = file.getChannel().map(FileChannel.MapMode.READ_WRITE, 0, 128);
// Do something
buffer.putInt(4);
} finally {
file.close();
System.out.println("File closed");
}
System.out.println("Press any key...");
System.in.read();
System.out.println("Finished");
}
}
Before pressing the key, I try to delete the file manually in FAR Manager. But FAR says the file is locked:
The process cannot access the file because it is being used by another process.
Cannot delete the file
D:\temp\file
Object is being opened in:
Java(TM) Platform SE binary (PID: 5768, C:\Program Files\Java\jdk1.8.0_05\bin\javaw.exe)
Only after pressing a key does the application exit and I can delete the file.
What's wrong with my code?
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2 answers
Try it.
public class Test
{
public static void main(String[] args) throws Exception {
String filePath = "D:/temp/file";
RandomAccessFile file = new RandomAccessFile(filePath, "rw");
FileChannel chan = file.getChannel();
try {
MappedByteBuffer buffer = chan.map(FileChannel.MapMode.READ_WRITE, 0, 128);
// Do something
buffer.putInt(4);
buffer.force();
Cleaner cleaner = ((sun.nio.ch.DirectBuffer) buffer).cleaner();
if (cleaner != null) {
cleaner.clean();
}
} finally {
chan.close();
file.close();
System.out.println("File closed");
}
System.out.println("Press any key...");
System.in.read();
System.out.println("Finished");
}
}
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@ SANN3's answer no longer works in Java 9. There is a new method in Java 9 sun.misc.Unsafe.invokeCleaner
that can be used. Here's the working code:
MappedByteBuffer buffer = ...
// Java 9+ only:
Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
Field unsafeField = unsafeClass.getDeclaredField("theUnsafe");
unsafeField.setAccessible(true);
Object unsafe = unsafeField.get(null);
Method invokeCleaner = unsafeClass.getMethod("invokeCleaner", ByteBuffer.class);
invokeCleaner.invoke(unsafe, buffer);
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