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up vote 1 down vote favorite

This is a method to read show details from a .ser file containing serialized objects of type Show. The method successfully return the list but gives an Exception before. Why is it so and how do I get rid of it?

public List<Show> populateDataFromFile(String fileName) {
        List<Show> shows=new ArrayList<Show>();
        ObjectInputStream obj=null;
    try {
        FileInputStream fin=new FileInputStream(fileName);
        obj=new ObjectInputStream(fin);
        Show show=null;
        while((show=(Show) obj.readObject())!=null)
        {
            shows.add(show);
            show.getShowName();
        }
        System.out.println(shows);
    } catch (IOException e) {
        e.printStackTrace();
    }catch(ClassNotFoundException e)
    {
        e.printStackTrace();
    }finally
    {
        try {
            obj.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    return shows;
}

The output is

java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2571)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1315)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
at com.util.DataManagerImpl.populateDataFromFile(DataManagerImpl.java:23)
at com.psl.Client.main(Client.java:9)
Show Name: Sahi re Sahi
Show Time: 6:30 PM
Seats Available: 40
Show Name: Ek Shyam Aapke Naam
Show Time: 6:30 PM
Seats Available: 40
Show Name: Moruchi Maushi
Show Time: 6:30 PM
Seats Available: 40
Show Name: All The Best
Show Time: 6:30 PM
Seats Available: 40
Show Name: Naksharanche Dene
Show Time: 6:30 PM
Seats Available: 40

The main method is

public static void main(String[] args) {
    DataManager dm=new DataManagerImpl();
    List<Show>shows=dm.populateDataFromFile("ShowDetails.ser");
    // Call all the functionalities from here to test your code.    
    for(Show show:shows)
    {
        System.out.println("Show Name: "+show.getShowName());
        System.out.println("Show Time: "+show.getShowTime());
        System.out.println("Seats Available: "+show.getSeatsAvailable());
    }
}
share|improve this question
1  
The list is returned regardless, cause the exception is caught, and hence does not halt execution of the method, it returns normally. Now if some data had been added to the list, those data will be returned –  maress Jun 20 at 13:38
    
That makes sense but even after getting rid of the finally block and closing the streams just after while loop I get the same error. –  rohit.agrawal Jun 20 at 13:44

2 Answers 2

up vote 3 down vote accepted

Because you've reached the end of the file.

You seem to think that readObject() returns null at end of file. It doesn't. It returns null if and only if you wrote a null.

The correct test is to catch EOFException and break, not to read until readObject() returns null.

share|improve this answer
    
Do you mean I can use a condition like while(1) and do the deserializing inside loop?If so. Can you give an example? –  rohit.agrawal Jun 20 at 14:04
    
You've just given an example yourself. It's not difficult. –  EJP Jun 20 at 15:50
up vote 2 down vote

EJP is correct that the error happens because the method readObject() does not return NULL when there is no more Show in the file.

EJP also has suggested a solution. I just want to suggest several other solutions, but instead of fixing the code that read the file, the solutions fix the code that write the file.

Currently, the file is generated by calling writeObject() method multiple times, each with a Show object. Instead of doing this you can:

  1. Create a List object that holds the shows. Write this List into file. When you read this file, you can just read the List back. You don't have to use while loop, and therefore, avoid the EOF exception check.

  2. Write the number of shows first to the file. After that, write the shows, one by one, to the file. When you read the file, you need to first read the number of shows, which informs you how many shows to read from the file. This will avoid the EOF exception check.

share|improve this answer
    
It won't avoid the EOFException check. There can't be any guarantee that the writing process actually wrote the number of objects specified by the header count. It could have written fewer and then been interrupted, or failed somehow. It could even have written more. You still have to deal with EOFException. –  EJP Jun 20 at 15:49
    
@EJP That is correct. I am assuming that the file is intact. That is to say, the file can be written without any problem. If don't assume this, we may get other exceptions, not just EOFException. –  fajarkoe Jun 20 at 15:52

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