Read objects from binary files in java

Question

I have function to serialize object and store it in a binary file, and also another object just to count how many objects I have stored on the file so far, so I can use the counter later to go through the file and deserialize it and read it. Here is my write function:

Class2 dad = new Class2(DadName.getText(), DadLastName.getText());

Class1 son = new Class1(FirstName.getText(), dad, "Session");

// Write object to  file
FileOutputStream outStream = new FileOutputStream(new File("MainStore.dat"), true);
ObjectOutputStream objectOutputFile = new ObjectOutputStream(outStream);
objectOutputFile.writeObject(son);
objectOutputFile.close();


// Update the objectcounter file by 
// Maintenance is a class I use just to save object contain information about number of files,increase them, decrease them.

Maintenance check = new Maintenance();
FileInputStream inStream = new FileInputStream("Counter.dat");
ObjectInputStream objectInput = new ObjectInputStream(inStream);
check = (Maintenance) objectInput.readObject();
inStream.close();

check.increaseObject();

FileOutputStream outStream1 = new FileOutputStream("Counter.dat");
ObjectOutputStream objectOutputFile1 = new ObjectOutputStream(outStream1);

objectOutputFile1.writeObject(check);
objectOutputFile1.close();

The previous function works just fine, the next step is function to read read the objects back from file, I use Counter.dat to see the number of Objects stored on MainStore.dat and it gives me the right number. Here is the read function:

// Read Counter file to know how many stored objects to go through them
Maintenance check = new Maintenance();
FileInputStream inStream = new FileInputStream("Counter.dat");
ObjectInputStream objectInput = new ObjectInputStream(inStream);
check = (Maintenance) objectInput.readObject();
int Counter1 = check.getObjectsNumber(); // function I created in the Maintenance class to return number of object stored
inStream.close();


// Read the stored objects
//here is my problem begin

FileInputStream inStream2 = new FileInputStream("MainStore.dat");
ObjectInputStream objectInputFile = new ObjectInputStream(inStream2);

// Create array of objects
Class1[] arrayOfObjects = new Class1[Counter1];

// Read the serialized objects from the file.
for (int i = 0; i < Counter1; i++) {
 arrayOfObjects[i] = (Class1) objectInputFile.readObject(); // here is the error pointed by compiler
}
objectInputFile.close();

for (int i = 0; i < 2; i++) {
 // here I should have array of all objects ready to read details

}

Everything looks fine except the last bit "// Read the serialized objects from". it gives me this error

Caused by: java.io.StreamCorruptedException: invalid type code: AC
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at registerController.CheckPlaceAvailabilityAction(registerController.java:120)
    ... 58 more

and When I tested it with only reading one object, it worked perfect and return the first stored object for me, the error happened when I try to read all stored objects.

You might want to post an MVCE(stackoverflow.com/help/mcve) if you can. — Luke Melaia
– Luke Melaia, Commented Dec 25, 2016 at 20:14
Why do you want to persist the counter? Are you sure your file did not get corrupted somewhere during testing? I suggest deleting it and starting over with a new file. — JimmyB
– JimmyB, Commented Dec 25, 2016 at 20:59

JimmyB · Accepted Answer · 2016-12-25 21:07:22Z

1

Apparently, you cannot transparently concatenate/append ObjectOutputStreams like you do.

See the docs:

[The] constructor writes the serialization stream header to the underlying stream

So a new stream will write some headers first, which would require a new input stream to read. Otherwise, the input stream will try to read the headers as a serialized object and will fail because those headers are not valid serialized object data.

answered Dec 25, 2016 at 21:07

JimmyB

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