Workaround java.io.EOFException cause by ObjectInputStream

Question

For my application I want to use a Map to act as a database. To save and load a map, I am writing/reading it to/from database.ser using this 2 methods:

private synchronized void saveDB() {
    try {
        fileOut = new FileOutputStream(db);
        out = new ObjectOutputStream(fileOut);
        out.writeObject(accounts);
        fileOut.close();
        out.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

@SuppressWarnings("unchecked")
private void loadDB() {
    try {
        fileIn = new FileInputStream(db);
        in = new ObjectInputStream(fileIn); // that is where error is produced if fileIn is empty
        accounts = (Map<String, Client>) in.readObject();
        in.close();
        fileIn.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

I want to load into Map when application starts, so I invoke method in constructor like this:

protected DriveatorImpl() {
    accounts = new ConcurrentHashMap<String, Client>();
    db = new File("C:/Users/eduar/git/Multy-Threaded-Bank-System/Bank-Services/database.ser"); 
// also, any suggestions how can I make path to a file more flexible in case I want to run Server side of an app on different machine?
     if (!db.exists()) {
        try {
            db.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
     }
    loadDB(); // loads database when server start 
}

I am aware of what causing an error, but I don't know what should I change in my design to avoid ObjectInputStream constructor receiving empty stream! Any suggestions on what I can do differently?

Edit: I want to note that in fresh application run database.ser is empty since there was no entries made into Map yet.

Thank You!

score 0 · Accepted Answer · edited May 23 '17 at 11:45

0

First why the EOFExcpetion occur?

There are no contents in file or file is empty and you tried to read file.
- You can avoid the EOFException for an empty file by checking file content length if it is less than or equal to zero means file is empty. another way to check if file is empty

Some code change and it worked for me.

@SuppressWarnings("unchecked")
private void loadDB() {
    try {
        if (db.length() <= 0) {
            // if statement evaluates to true even if file doesn't exists
            saveDB(); // save to a file an empty map
                      // if file doesn't exist, it creates a new one 
                      // call loadDB inside constructor

        }
        FileInputStream fileIn = new FileInputStream(db);
        ObjectInputStream in = new ObjectInputStream(fileIn); // that is where error is produced if fileIn is empty
        in.readObject();
        in.close();
        fileIn.close();
        System.out.println(accounts);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

edited May 23 '17 at 11:45

Community

1
1

answered Jan 13 '17 at 09:08

Gopinath Langote

311
4
10

I can't make head or tail of #2, and the second bullet point is equally meaningless. Your 'another way' is exactly the same as your original way of checking for emptiness. – user207421 Jan 13 '17 at 09:19
I think checking for empty file and returning from method is exactly what I needed! I am calling saveDB() in methods where I am putting or modifying values in map to insure all data is saved in case server crashes. I think I understand now why calling saveDB() method in constructor before loadDB() would work. It writes to a file an empty map, but still some bytes going through the stream. Only problem is, if I have some values already stored in Map and I save it to a file, subsequent instantiation of a class will overwrite file with empty map and all data will be lost. Thank you for your help! – GarRudo Jan 13 '17 at 09:24
You are welcome. Please try to avoid the duplicate question as @EJP mentioned. It will help to avoid mess up. Thank you. – Gopinath Langote Jan 13 '17 at 10:06
I don't agree with @EJP that question is duplicated. Last question was about path to a file and File Not Found Exception. An additional error was revealed during a review that cause EOFExcpetion and has to do with empty stream being passed to an ObjectInputStream constructor. I think this question requires individual attention. – GarRudo Jan 13 '17 at 10:15
@GarRudo Please tick to the answer I have submitted for your problem so that, other people can see that, this solved your issue. Thank you. – Gopinath Langote Jan 13 '17 at 12:05
Fixed. Thank you. – GarRudo Jan 14 '17 at 18:43

score 0 · Answer 2 · answered Jan 13 '17 at 09:18

0

Get rid of the file.exists()/file.createNewFile() crap. All it is doing for you is masking the original FileNotFoundException problem, and turning into a thoroughly predictable EOFException because of trying to construct an ObjectInputStream around an empty stream. Handle the original problem. Don't just move it, or turn it into something else.

answered Jan 13 '17 at 09:18

user207421

305,947
44
307
483

I understand now when read your comment to original post. This would be a graceful solution I need. Thank you. – GarRudo Jan 13 '17 at 09:48

Workaround java.io.EOFException cause by ObjectInputStream

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