java - BufferOverflowException 的原因是什么？

Question

异常堆栈为

java.nio.BufferOverflowException
     at java.nio.DirectByteBuffer.put(DirectByteBuffer.java:327)
     at java.nio.ByteBuffer.put(ByteBuffer.java:813)
            mappedByteBuffer.put(bytes);

代码:

randomAccessFile = new RandomAccessFile(file, "rw");
fileChannel = randomAccessFile.getChannel();
mappedByteBuffer = fileChannel.map(MapMode.READ_WRITE, 0, file.length());

并调用mappedByteBuffer.put(bytes);

mappedByteBuffer.put(bytes) 抛出 BufferOverflowException 的原因是什么
如何查找原因？

Answer 1

FileChannel#map :

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

换句话说，如果bytes.length > file.length()，您应该收到一个BufferOverflowException。

为了证明这一点，我测试了这段代码:

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);
}

当且仅当打印 true 时，才会抛出此异常:

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