Thread: Error reading objects from file

Hi,
I am trying to put objects in a file and later want to read them.
I am using following code to add objects in file
//for adding object in file

public void addObject() throws IOException, ClassNotFoundException
{
        ObjectOutputStream objs=new ObjectOutputStream(new FileOutputStream("x:\\ABCD1.dat",true));
        MyClass o1=new MyClass("abc", "abc");
        MyClass o2=new MyClass("cde", "pqr");
        objs.writeObject((Object)o1);
        objs.writeObject((Object)o2);
        objs.flush();
        objs.close();
}

And to read object from file i am using following code

public void getObject() throws FileNotFoundException, IOException
{
        ObjectInputStream obji=new ObjectInputStream(new FileInputStream("x:\\ABCD1.dat"));
        MyClass my=null;
        boolean flag=true;
        while(flag==true)
        {
            try
            {
                my=(MyClass)obji.readObject();
                System.out.println(""+my.str1);
                System.out.println(""+my.str2);
            }
            catch(Exception e)
            {
                System.out.println("Now in catch\n"+e);
                flag=false;
            }
        }
        obji.close();
}

This works fine if i add two object on calling a addObject() function.
But if i modify my addObject() function as shown below

public void addObject() throws IOException, ClassNotFoundException
 {
        //adding object inside file
        ObjectOutputStream objs=new ObjectOutputStream(new FileOutputStream("x:\\ABCD1.dat",true));
        MyClass o1=new MyClass("abc", "abc");
        objs.writeObject((Object)o1);
        objs.flush();
        objs.close();
}

Now when i call this function twice from my main() function it adds two object in file(when i viewed file externally i can see two objects there).
But when i call getObject() function it reads only one object from file and on trying to read second object it gives following error.
java.io.StreamCorruptedException: invalid type code: AC
No matter how many object i insert in a file it reads only first object and then gives above error.
I am unable to understand what is going wrong in this please help.

Thanks in advance.

Can you post runnable code that demonstrates the error?

Originally Posted by GregBrannon

Can you post runnable code that demonstrates the error?

First and second code snippet i have given for inserting and reading object works fine.
I am using following code to run it.

public static void main(String args[]) throws IOException, ClassNotFoundException
    {
        FileHandlingObject_Trial1 o1=new FileHandlingObject_Trial1();
        o1.addObject();
        o1.getObject();
    }

Problem occurs when i modify my addObject() method as shown in second code snippet. getObject() method is same but it reads only one object this time.(in previous case it reads two objects correctly).
For second time i am using following code to run it.
public static void main(String args[]) throws IOException, ClassNotFoundException
{
FileHandlingObject_Trial1 o1=new FileHandlingObject_Trial1();
o1.addObject();
o1.addObject();
o1.getObject();

}

I believe andbin answered your question.

Hey guys thanks for your answers.
What andbin said is correct each time it adds header before adding object.
But i figured out that this happens because of following line of code.
ObjectOutputStream objs=new ObjectOutputStream(new FileOutputStream("x:\\ABCD1.dat",true));

if i remove this line from addObject() function and place it in void main i can add as many objects as i want.
It reads object correct with same getObjectFunction().
I am posting modified code.

public static void main(String args[]) throws IOException, ClassNotFoundException
    {
        FileHandlingObject_Trial1 o1=new FileHandlingObject_Trial1();
        o1.objs=null;
        [COLOR="#FF0000"]o1.objs=new ObjectOutputStream(new FileOutputStream("x:\\ABCD1.dat",true));[/COLOR]
        o1.addObject();
        o1.addObject();
        o1.getObject();
 
    }
    public void addObject() throws IOException, ClassNotFoundException
    {
        //adding object inside file
//        objs=new ObjectOutputStream(new FileOutputStream("x:\\ABCD1.dat"));
        MyClass o1=new MyClass("abc", "abc");
        objs.writeObject((Object)o1);
        objs.flush();
//        objs.close();

getObject function is same as stated previously.


Thanks a lot for your help guys.

Originally Posted by andbin

But you have not solved much more .... you are still opening the file in "append" mode. If you run the app 2 times, you corrupt the stream as I have described.

I am completely agree with you. Opening file in append more corrupts file.
I tried it.
Thanks for your suggestions.