What is the cause of BufferOverflowException?

java, nio

Solution

FileChannel#map:

The mapped byte buffer returned by this method will have a position of zero and a limit and capacity of size;

In other words, if `bytes.length > file.length()`, you should receive a `BufferOverflowException`.

To prove the point, I have tested this code:

File f = new File("test.txt");
try (RandomAccessFile raf = new RandomAccessFile(f, "rw")) {
  FileChannel ch = raf.getChannel();
  MappedByteBuffer buf = ch.map(MapMode.READ_WRITE, 0, f.length());
  final byte[] src = new byte[10];
  System.out.println(src.length > f.length());
  buf.put(src);
}

If and only if `true` is printed, this exception is thrown:

Exception in thread "main" java.nio.BufferOverflowException
at java.nio.DirectByteBuffer.put(DirectByteBuffer.java:357)
at java.nio.ByteBuffer.put(ByteBuffer.java:832)

Problem

The exception stack is ``` java.nio.BufferOverflowException at java.nio.DirectByteBuffer.put(DirectByteBuffer.java:327) at java.nio.ByteBuffer.put(ByteBuffer.java:813) mappedByteBuffer.put(bytes); ``` The code: ``` randomAccessFile = new RandomAccessFile(file, "rw"); fileChannel = randomAccessFile.getChannel(); mappedByteBuffer = fileChannel.map(MapMode.READ_WRITE, 0, file.length()); ``` and call `mappedByteBuffer.put(bytes);` What is the cause `mappedByteBuffer.put(bytes)` throws BufferOverflowException How to find the cause ?

Original source