ObjectOutputStream in try-with-resources

Question

I am using ObjectOutputStream to write the data into a file. Following is the code snippet.

try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(f))) 
{
    oos.writeObject(allObjects);
}

Questions:

Do I need to split the object construction of OOS and FOS separately in try-with-resources? I assume that OOS internally also closes the FOS. So the above code line should be fine.
Do I need to explicitly call flush?

The problem being I saw once the file was corrupted and while debugging I had the above mentioned queries.

The implementation of OOS in my JVM (Oracle) flushes the stream and closes it when OOS.close() is called. — nickb, Mar 21 '18 at 17:57
http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/io/ObjectOutputStream.java#ObjectOutputStream.close%28%29 — hovanessyan, Mar 21 '18 at 18:02
I was about to post the same as @hovanessyan, it's always good to look by yourself. — Nyamiou The Galeanthrope, Mar 21 '18 at 18:06

score 6 · Accepted Answer · answered Mar 21 '18 at 18:00

6

No: Closing ObjectOutputStream will automatically close FileOutputStream
No: The stream will be flushed automatically on close.

answered Mar 21 '18 at 18:00

Maciej

1,954
10
14

score 2 · Answer 2 · answered Nov 08 '19 at 18:38

I believe developers should rely on the published general contract.

There is no evidence that an ObjectOutputStream's close() method calls flush().

OpenJDK's ObjectOutputStream#close is just a vendor implementation, I believe.

And it won't hurt if we flush on the try-with-resources.

try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(f))) {
    oos.writeObject(allObjects);
    oos.flush(); // What's possibly going wrong with this?
}

ObjectOutputStream in try-with-resources

2 Answers2