CODEWITHSUNDEEP
javafilestreambinaryappend
user13764634
user13764634

Reputation: 21

Appendable Binary File

I'm working on appending objects to a binary file. My file is: 

File f=new File("person.dat");

I'm getting an error (java.io.StreamCorruptedException: invalid stream header: 79737200) when I attempt to open the binary file. As far as I can tell the program writes the data just fine, but as soon as I try reading from it, I get the above error. Any help is appreciated!

My Code to write:

AppendObjectOutputStream out = null;

try {
    out = new AppendObjectOutputStream(new FileOutputStream(f, true));
    out.writeObject(new Student(name, age));
    out.flush();

     } 
catch (Exception ex) {
    ex.printStackTrace();
     } 
 finally {
    out.close();
     }

My class for making appendable:

public class AppendObjectOutputStream extends ObjectOutputStream {

    public AppendObjectOutputStream(OutputStream out) throws IOException {
        super(out);
    }

    @Override
    protected void writeStreamHeader() throws IOException {
        reset();
    }
 }

My partial code for reading and adding objects to an ArrayList:

Course course = new Course();
Student st = null;
ObjectInputStream in = null;
try {
    in = new ObjectInputStream(new FileInputStream("person.dat"));

    try 
      {
        while (true) 
         {
            st = (Student) in.readObject();
            course.addAccount(st); //adds student object to an ArrayList in 
                                   //class Course
          }
      } 
    catch (EOFException ex) {
    }
  } 
  catch (Exception ex) {
    ex.printStackTrace();
  } finally {
    in.close();
  }

UPDATE: Current code to read but its not printing anything to screen:

try(ObjectInputStream ois = new ObjectInputStream(
                        new BufferedInputStream(Files.newInputStream(f))))
 {
            while (ois.available() > 0) 
            {

                    st = (Student) ois.readObject();
                    studentlist.addAccount(st);
                    System.out.println(st.getStudentNumber());
                }

            }

 catch (Exception ex) 
                {
                    ex.printStackTrace();
                }

This is how I write to file:

Path f = Paths.get("person.dat");

   try (ObjectOutputStream oos = new ObjectOutputStream(
           new BufferedOutputStream(Files.newOutputStream(f, StandardOpenOption.APPEND))))
   {
       oos.writeObject(new Student(name,age));    
   }
   catch(Exception ex)
   {
       ex.printStackTrace();
   }

Upvotes: 2

Views: 242

Answers (2)

user13764634
user13764634

Reputation: 21

I have modified the code to work around making a file "appendable". I write a single arraylist object to the file (the arraylist holds a list of student objects). When I want to add a student, I read the object (arraylist) from the file, add my new student to the arraylist and write the arraylist back to the file. It is now working and my file does not have an append format.

Upvotes: 0

Puce
Puce

Reputation: 38142

Rather than trying to fix your utility classes, I suggest to use the standard classes of the NIO.2 File API.

Try something like (untested):

    Path personDataFilePath = Paths.get("person.dat");
    // or Java 11:
    // Path personDataFilePath = Path.of("person.dat");
    try (ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(Files.newOutputStream(personDataFilePath, StandardOpenOption.APPEND)))){
        oos.writeObject(new Student(name,age));
    } catch (IOException ex) {
        // do some error handling here
    }

and to read the file, something like (untested):

    List<Student> students = new ArrayList<>();
    try (ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(Files.newInputStream(personDataFilePath)))){
        while (ois.available() > 0){
            students.add((Student) ois.readObject());
        }
    } catch (IOException ex) {
        // do some error handling here
    }

Upvotes: 1

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