Java help (reading a binary database) - Overclock.net

*dangerousHobo* · 03-30-07

Well I have a database of recipes and the database is a binary file.

I'm able to take a recipe write it to the database, close the outputStream, create an inputStream, and read the database, however I've added multiple recipes to the database. I want to be able to open up the database and print everything that is inside it.

Everything that got written to the database got written as an object.

The method:

Code:

public void printWholeDatabase(String database){
		ObjectInputStream inStream = null;
		IngredientList recipe=null;
		try{
			inStream = new ObjectInputStream(new FileInputStream(database));
			while(true){
				recipe=(IngredientList)inStream.readObject();
				System.out.println(recipe);
			}
		}
		catch(ClassNotFoundException e){
			
		}
		catch(FileNotFoundException e){
			
		}
		catch(IOException e){
			
		}
	}

My problem is that it is only reading the first thing that I entered into the database.

I know I'm not making a new database file b/c the size of the file just keeps getting bigger.

Any Ideas.

decompiled · 03-31-07

Try something like this:

Code:

try {
  s = new Scanner(new BufferedReader( new FileReader(args[0])));

  while ( s.hasNext() )
  {
    String file = s.nextLine();
    parse(file);  // This is your parsing method.  Not sure what you used.  Newline would work well I'm guessing...
  }

} finally {
  if ( s != null )
    s.close();
}

*** Edit ***

I looked at your code. The way I thought of the issue was to store data in the database and then assemble the object from that data when reading back in. You have chosen to do it slightly different however the idea should still be the same. You will want to have a conditional that loops through the file. In my example hasNext() does that for you. The conditional is met when the null character is found. Namely the end of the file. The API explains this better =).

*dangerousHobo* · 03-31-07

Edit::

Quote:

<Edit::>
I just found out that I'll have to read everything from the file(probably add it to an arrayList and then add the new recipe in and then write the new arrayList to the database file, overwriting the old file and not appending to it. I guess when java writes the header file to the binary file it says how long it is. SO after adding a new object to the file it still thinks that it is the same size after the fisrt entry. I guess there are ways around this, just given the timeline of this project it would be to difficult. So problem solved for know, I'll just have to make a class that manages the database with and arrayList.

<end::Edit>

I don't want to have to "assemble the object from that data when reading back in", thats way I want about and wrote it to the database as an Object. It save work and less code. I'm working with binary files too so, Scanner and nextLine, etc, don't exists.

I just don't get why its read the first object and then when it goes to read the second it throws a IOException.

I wrote this program to test out reading an object from a file, and it works fine, so I don't get why it wont here.

The test program though:

Code:

import java.io.Serializable;


public class Abc implements Serializable{

	static int count = 0;
	int i;
	Abc()
	{
		i = ++count;
		System.out.println("Count Add "+count);
	}
	public String toString()
	{
		return "Count "+i;
	}
}

Code:

import java.io.EOFException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;


public class Test1 {

	
	public static void main(String[] args)throws Exception {
		ObjectOutputStream oop = new ObjectOutputStream(new FileOutputStream("test.dat"));
		Abc a[] = new Abc[5];	
		int i = 0;
		while(i < 5)
		{
			a[i++] = new Abc();
		}
		i = 0;
		while(i < 5)
		{
			oop.writeObject(a[i++]);
		}
		oop.close();
		Abc temp = null;
		ObjectInputStream oip = new ObjectInputStream(new FileInputStream("test.dat"));
		try
		{
			while((temp = (Abc)oip.readObject()) != null)
			{
				System.out.println(temp.toString());
			}
		}
		catch(EOFException e)
		{
			System.out.println("All objects read. End Of File");
		}
                oip.close();
	}

}

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Java help (reading a binary database)

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