read/write an object to file

Question

here is the code : my mission is to serialize an my object(Person) , save it in a file in android(privately), read the file later,(i will get a byte array), and deserialize the byta array.

       public void setup()
    {

           byte[] data = SerializationUtils.serialize(f);


             WriteByteToFile(data,filename); 



    }
Person p =null ;
    public void draw()
    {
        File te = new File(filename);
         FileInputStream fin = null;


             try {
                fin=new FileInputStream(te);
                byte filecon[]=new byte[(int)te.length()];
                fin.read(filecon);
                String s = new String(filecon);
                System.out.println("File content: " + s);
            } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }






        text(p.a,150,150);

    }

and my function :

public void WriteByteToFile(byte[] mybytes, String filename){

        try {

        FileOutputStream FOS = openFileOutput(filename, MODE_PRIVATE);
        FOS.write(mybytes);
        FOS.close();


        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("done");









    }

it is returning a filenotfoundexception .

(i am new at this, so please be patient and understanding)

EDIT ::this is how i am (trying to ) read, (for cerntainly)

ObjectInputStream input = null;
    String filename = "testFilemost.srl";
    try {
        input = new ObjectInputStream(new FileInputStream(new File(new File(getFilesDir(),"")+File.separator+filename)));
    } catch (StreamCorruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        Person myPersonObject = (Person) input.readObject();
        text(myPersonObject.a,150,150);
    } catch (OptionalDataException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        input.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

and for reading :::

if(mousePressed)

{
    Person myPersonObject = new Person();
    myPersonObject.a=432;
    String filename = "testFilemost.srl";
    ObjectOutput out = null;

    try {
        out = new ObjectOutputStream(new FileOutputStream(new File(getFilesDir(),"")+File.separator+filename));
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        out.writeObject(myPersonObject);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        out.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

you don't have file in filesystem. First create a file then open it. — Ashwani, Aug 11 '13 at 07:43

growic · Accepted Answer · 2013-08-14T08:17:27.237

19

You don't need to use the 'byte array' approach. There is an easy way to (de)serialize objects.

EDIT: here's the long version of code

Read:

public void read(){
    ObjectInputStream input;
    String filename = "testFilemost.srl";

    try {
        input = new ObjectInputStream(new FileInputStream(new File(new File(getFilesDir(),"")+File.separator+filename)));
        Person myPersonObject = (Person) input.readObject();
        Log.v("serialization","Person a="+myPersonObject.getA());
        input.close();
    } catch (StreamCorruptedException e) {
        e.printStackTrace();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

}

Write:

public void write(){
    Person myPersonObject = new Person();
    myPersonObject.setA(432);
    String filename = "testFilemost.srl";
    ObjectOutput out = null;

    try {
        out = new ObjectOutputStream(new FileOutputStream(new File(getFilesDir(),"")+File.separator+filename));
        out.writeObject(myPersonObject);
        out.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Person class:

public class Person implements Serializable {
    private static final long serialVersionUID = -29238982928391L;
    int a;

    public int getA(){
        return a;
    }

    public void setA(int newA){
        a = newA;
    }
}

edited Aug 14 '13 at 08:17

answered Aug 11 '13 at 08:07

growic

330
3
11

i just need to store it in internal directory. – harveyslash Aug 11 '13 at 16:20
You just have to use getFilesDir() instead of Environment.getExternalStorageDirectory() – growic Aug 12 '13 at 10:27
i cant seem to get it to work. in my void setup, i am reading it. (void setup runs only once). and in my void draw, i am checking for a touch,if true, it writes an object to the file. the next time i run the app, the value read in void setup is still 0. i dont know what is wrong. – harveyslash Aug 12 '13 at 16:23
also, what is the location of this file that (has not yet)is being saved? – harveyslash Aug 12 '13 at 16:52
It's in Data > Data > app.package.name > files – growic Aug 13 '13 at 00:33
^i can see the file getting created,but in reading, it is not printing the assigned value. – harveyslash Aug 13 '13 at 02:32
can you show me your code (the part you write and read including the line where you created your object)? – growic Aug 13 '13 at 05:40
see my edit. I've tested my code. It would work for you, too. – growic Aug 14 '13 at 08:18
YES! thats what i was talking about. thank you brother! (btw, was the way i was acessing the object the problem?) – harveyslash Aug 15 '13 at 07:51
I'm not sure why you got a '0' value. You'd have to dig through your stack trace. PS. Please keep in mind that you cannot serialize a nested class (a class within a class). Cheers. – growic Aug 15 '13 at 11:36
okay, will surely keep that in mind could you give me your email id, where i could contact you ? – harveyslash Aug 15 '13 at 13:31

score 1 · Answer 2 · answered Aug 14 '13 at 08:39

1

FileNotFoundException when creating a new FileOutputStream means that one of the intermediate directories didn't exist. Try

file.getParentFile().mkdirs();

before creating the FileOutputStream.

answered Aug 14 '13 at 08:39

user207421

305,947
44
307
483

Kanan · Answer 3 · 2022-10-10T14:25:25.417

Add this code to manifest.xml

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"/>

Go to phone setting/applications/your_app/permissions/ allow files and media permission. You can ask permission via by code and when user enter app program will ask permission. If you want I can give you code.

All writen and readen objects must be serializable.(Must implements Serializable interface) If A class extends B class, to set B class serializable is enough. And add this code to writen and readen class:

    private static final long serialVersionUID = 1L;

Write to external memory:

public static void writeToExternal(Serializable object, String filename) {
    try {
        //File root = new File(Environment.getExternalStorageDirectory(), "MyApp");
        //or
        File root = new File("/storage/emulated/0/MyApp/");
        if (!root.exists()) {
            root.mkdirs();
        }
        File file = new File(root, filename);
        FileOutputStream fos = new FileOutputStream(file);
        ObjectOutput out = new ObjectOutputStream(fos);
        out.writeObject(object);
        out.flush();
        out.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

If you want to write to internal memory(This memory is not visible and doesn't need permission. This is your app stored in. For this, you can use getFilesDir() instead of getExternalStorageDirectory(). More about https://developer.android.com/reference/android/content/ContextWrapper#getFilesDir%28%29 https://developer.android.com/reference/android/os/Environment.html#getDataDirectory%28%29 https://gist.github.com/granoeste/5574148 https://source.android.com/docs/core/storage

public static void writeToInternal(Context context, Serializable object, String filename){
    try {
        //File root1 = new File(context.getFilesDir(), "MyApp");
        //or
        File root = new File("/data/user/0/com.example.myapplication/files/MyApp/");
        if (!root.exists()) {
            root.mkdirs();
        }
        File file = new File(root, filename);
        FileOutputStream fos = new FileOutputStream(file);
        ObjectOutput out = new ObjectOutputStream(fos);
        out.writeObject(object);
        out.flush();
        out.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Read an object:

public static Object read(String filename) {
    try {
        File file = new File("/storage/emulated/0/MyApp/" + filename);
        FileInputStream fis = new FileInputStream(file);
        ObjectInputStream input = new ObjectInputStream(fis);
        Object data = (Object) input.readObject();
        input.close();
        return data;
    } catch (StreamCorruptedException e) {
        e.printStackTrace();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
    return null;
}

When you call read method you must cast to your readen and writen class.(For example Person p = (Person)read("file.txt"); Import all classes and run.

read/write an object to file

3 Answers3