Binary file I/O with custom object - Java

Question

I am trying to write data to a binary file and am having difficulty. When I run this method I don't get any output to the file. Also when it comes to writing my "Date" object, I can't seem to find a write method that takes it as a parameter. The object consists of an int month, day, and year. How can I write it into a binary file properly?

Also, does "File" work for binary as well? I have only previously used it for regular .txt files and I'm not sure if it can be used the same way in this situation. Thanks!

Here is my write method:

private void writeBinary(){
    //String fileName = getUserInput();
    String fileTest = "BinaryMonster.bin";
    File file = new File(fileTest);
    DataOutputStream out;

    try{
       out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(file, true)));

       if(!(file.exists())){
           file.createNewFile();
           System.out.println("New file created...");
       }

       for(int i = 0; i < monsterAttacks.size(); i++){
           out.writeInt(monsterAttacks.get(i).getID());
           out.write(monsterAttacks.get(i).getDate()); //getting error
           out.writeUTF(monsterAttacks.get(i).getName() + monsterAttacks.get(i).getLocation() + monsterAttacks.get(i).getReporter());

       }

    } catch(IOException e) {
        e.printStackTrace();
    }
}

//getting error -- What error? Please show the full error message. Also, you appear to be writing mostly text to the file -- why not output the data as a text file such as a JSON or XML file? Or as a serialized file via ObjectOutputStream? — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Nov 18, 2017 at 19:10
But even after you fix this, your code is broken as it will be very difficult for you to retrieve any usable data from this file as you've wired it. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Nov 18, 2017 at 19:14
Do you have any suggestions for me to fix it? @HovercraftFullOfEels — Max Orozco
– Max Orozco, Commented Nov 18, 2017 at 19:21

Rehan Javed · Accepted Answer · 2017-11-18 19:12:19Z

1

It is giving error because you are writing whole object of date into the file using DataOutputStream, which don't allow you to do that.

Write it in the form of String into the file. It will be better.

out.writeUTF(monsterAttacks.get(i).getDate().toString());

But if you want to save the whole object into the file, then you need to use ObjectOutputStream which write whole serialized objects into the file.

And it is better approach to flush and close the file.

out.flush();
out.close();

answered Nov 18, 2017 at 19:12

Rehan Javed

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