How to read from text file into array of Objects

Question

So i looked over a couple of solutions but none of them worked for me. Thanks for some folks i got the infinite cycle right in the end, but it still doesnt work for me. I want to read a file "output.txt" into a list of objects. So i provide the remaining codes since i thought they wouldnt help at all...

try {
            List<House> listH = new ArrayList<>();
            boolean cont = true;
            ObjectInputStream ois = new ObjectInputStream(new FileInputStream("output.txt"));
            while(cont)
            {
                House house = (House) ois.readObject();
                if(house != null)
                    listH.add(house);
                else
                    cont = false;
            }
            ois.close();
            mainmenu();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }

The writing code:

try {
            FileWriter writer = new FileWriter("output.txt");
            for(House str : listH)
            {
                writer.write(String.valueOf(str) + "\n");
            }
            writer.close();
            System.out.println("Successful writing");
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("Couldn't write");
        }

The House Object:

public class House {
    String address;
    double area;
    boolean garage;

    public House(String address, double area, boolean garage){
        this.address=address;
        this.area = area;
        this.garage = garage;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public double getArea() {
        return area;
    }

    public void setArea(double area) {
        this.area = area;
    }

    public boolean isGarage() {
        return garage;
    }

    public void setGarage(boolean garage) {
        this.garage = garage;
    }

    @Override
    public String toString() {
        return address + ";" + area + ";" + garage;
    }
}

The error messages are the following:

java.io.StreamCorruptedException: invalid stream header: 3134313B at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:866) at java.io.ObjectInputStream.(ObjectInputStream.java:358)

An object Stream is a very specific binary format, not a text file. — Thorbjørn Ravn Andersen
– Thorbjørn Ravn Andersen, Commented Jun 9, 2019 at 10:09
Any comments on the answers you received so far? You see, all essential things have been said here. — GhostCat
– GhostCat, Commented Jun 9, 2019 at 13:01
I got it to work with a Scanner instead of ObjectInputStream — Chris
– Chris, Commented Jun 9, 2019 at 13:33
Then please consider accepting one of the answers. For example the one that tells you that you should carefully check whether you want to read TEXT or serialized binary objects ;-) — GhostCat
– GhostCat, Commented Jun 11, 2019 at 6:43

Japheth Ongeri - inkalimeva · Accepted Answer · 2019-06-09 10:13:54Z

1

You have three main problems:

Your while loop is infinite and may cause a stackoverflow error, make the condition check that there is another line/object to be read in the file before it proceeds.
The code that reads the file casts directly to a House object, this highly dependent on format of the file writing, any error will cause a failed read.
The else part of the condition checking if house is null breaks out of the whole reading process, so if there is one null house for any reason all houses after it will not be read For a more specific answer I may need House class structure and the process used to create the output file.Otherwise use hasnext in the while condition and readline to 'manually' construct a house object from string values.

answered Jun 9, 2019 at 10:13

Japheth Ongeri - inkalimeva

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Comments

GhostCat · Accepted Answer · 2019-06-09 10:10:33Z

0

This here:

ObjectInputStream ois = new ObjectInputStream(new FileInputStream("output.txt"));

is a contradiction in itself. You see, when you serialize java objects via the standard Java mechanism, you end up with bytes. Binary data.

Thus:

either your file has a wrong file extension (and is binary, not text) OR:
whatever you have in that file ... isn't binary data.

The exception implies that the second case is more likely.

In other words: verify what really is in that "output.txt" file. Obviously, not the result of serializing Java objects.

(note: of course, the file extension doesn't matter, but it implies that the file really is something different then what you expect it to be)

answered Jun 9, 2019 at 10:10

GhostCat

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