I am using the following method to read from the internal storage:
private void deserialize(ArrayList<Alias>arrayList) {
try {
FileInputStream fis = openFileInput(filename);
ObjectInputStream ois = new ObjectInputStream(fis);
arrayList = (ArrayList<Alias>)ois.readObject();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
It reads the content of the file "filename" to the "arrayList".
The "serialize" method is as follows:
void serialize(ArrayList<Alias>arrayList) {
FileOutputStream fos;
try {
fos = openFileOutput(filename, Context.MODE_PRIVATE);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(arrayList);
oos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
The problem is that I whenever I run my program again, the "arrayList" is empty. So I guess I am opening the file in wrong input mode.
My aim is to first get the array from the file, then modify it within the app, and then write the modified array back to the file.
Can someone please help me with my problem?
Thanks!
Can you post your pice of your source code? I think the way which you used to parse file content get issue.
Read here:
Android ObjectInputStream docs
I read that the method readObject() read the next object...i this that you must iterate with something like this:
MediaLibrary obj = null;
while ((obj = (MediaLibrary)objIn.readObject()) != null) {
libraryFromDisk.add(obj);
}
Related
I want to save all elements of a HashMap in a file. To do this I wrote following code with the help of some google searches:
public void saveCalendars() {
try {FileOutputStream fos = new FileOutputStream(CALENDARPATH_STRING);
ObjectOutputStream oos = new ObjectOutputStream(fos);
for(Calendar elementCalendar : calendarRegister.values()) {
oos.writeObject(elementCalendar);
}
oos.close();
fos.close();
} catch (FileNotFoundException e) {
System.out.println("File not found");
try {FileOutputStream fos = new FileOutputStream(new File(CALENDARPATH_STRING));
ObjectOutputStream oos = new ObjectOutputStream(fos);
for(Calendar elementCalendar : calendarRegister.values()) {
oos.writeObject(elementCalendar);
}
oos.close();
fos.close();
} catch (IOException ex) {
System.out.println("Creating: Error initializing stream");
}
} catch (IOException e) {
System.out.println("Save: Error initializing stream");
}
}
With final static String CALENDARPATH_STRING = "C:\\Windows\\calendars.dat";.
I thought that I simply could use the same Code but with FileOutputStream fos = new FileOutputStream(new File(CALENDARPATH_STRING)); if the file hasn't been created yet to create one.
Unfortunately, it doesn't work. It's the firs time, that a make such saving stuff, so maybe you can help me.
A couple of suggestions:
Use File.createNewFile to create a new file and verify it's result
Use try-with-resources when dealing with IO stuff (I assume you use > JDK 7). You can read more about this feature on official site.
You can avoid duplications:
File calendarFile = new File(CALENDARPATH_STRING);
try {
if(calendarFile.createNewFile()) {
System.out.println("File not found. New file was created");
}
} catch (IOException e) {
System.out.printf("Can not create file %s\n", CALENDARPATH_STRING);
}
try(FileOutputStream fos = new FileOutputStream(calendarFile);
ObjectOutputStream oos = new ObjectOutputStream(fos)) {
for(Calendar elementCalendar : calendarRegister.values()) {
oos.writeObject(elementCalendar);
}
} catch (IOException e) {
System.out.println("Save: Error initializing stream");
}
Well, I can see that there is an issue with the path of your file CALENDAR_PATH_STRING
and use new File(CALENDAR_PATH_STRING) it would create a new file if the particular file was not found. Also in local I can see it is working.
public void saveCalendars(Map<String, Calendar> calendarRegister) {
try (FileOutputStream fos = new FileOutputStream(new File(CALENDAR_PATH_STRING));
ObjectOutputStream oos = new ObjectOutputStream(fos)) {
for (Calendar elementCalendar : calendarRegister.values()) {
oos.writeObject(elementCalendar);
}
} catch (IOException e) {
System.out.println("Creating: Error initializing stream");
}
}
I have my program setup to serialize a certain Facebook Object on exit, and deserialize it on open. But I want to have an if statement in the deserialization portion to only go on with it if a serilization file is present to avoid errors. How can I do that? Is there anyway that I could refer to the file "serilaized" and check if it exists?
Deserialization portion:
Facebook facebook = null;
try {
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(
"serialized"));
facebook = (Facebook) ois.readObject();
ois.close();
} catch (FileNotFoundException e) {
System.err.println("Could not open the file \"serialized\"");
} catch (IOException e) {
System.err.println("Could not de-serialize the object");
} catch (ClassNotFoundException e) {
System.err.println("Could not cast the de-serialized object");
}
Serialization portion:
try {
ObjectOutputStream oos = new ObjectOutputStream(
new FileOutputStream ("serialized"));
oos.writeObject(facebook);
oos.close();
} catch (FileNotFoundException e) {
System.err
.println("Could not create the file \"serialized\"");
} catch (IOException e) {
System.err.println("Could not serialize the object");
}
The FileNotFoundException should catch the case where there is no file present to deserialize. Throwing the error is fine, so long as it is handled gracefully.
I am trying to write a Serialized Object in my onPause method into a file so that I can read it again from the file when I start the app another time and need the previous data.
This is where i save the Object
try {
FileOutputStream fout = openFileOutput(logFileName, MODE_PRIVATE);
ObjectOutputStream fw = new ObjectOutputStream(fout);
fw.writeObject(obj);
Log.d("obj", "added");
fw.close();
} catch (Exception e) {
Log.d("obj", "not added");
e.printStackTrace();
}
return;
I can see the "added" message and this means that the Object has been saved in the file.
Here is where i try to read the saved object:
try {
FileInputStream fin = openFileInput(logFileName);
ObjectInputStream fread = new ObjectInputStream(fin);
Object res = fread.readObject();
Log.d("obj", "readed successfully");
} catch (Exception e) {
e.printStackTrace();
}
And I get this :
java.io.InvalidClassException: android.view.View; IllegalAccessException
on the line calling "fread.readObject()". I would thank you if you could please tell me why is it throwing the following Exception.
Thanks in Advance.
I have this method supposed to read a file:
/* Read file's content */
private ArrayList<String> readFromFile() {
File file = new File("jokesBody1.bjk");
ArrayList<String> list = new ArrayList<String>();
try {
file.createNewFile();
ObjectInputStream ois = new ObjectInputStream( new FileInputStream( file ) );
try {
list = (ArrayList)ois.readObject();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
ois.close();
} catch (IOException e) {
Log.e("log activity", "Can not read file: " + e.toString());
}
return list;
}
When I call it, it returns:
02-16 06:15:32.686: E/log activity(1380): Can not read file: java.io.IOException: open failed: EROFS (Read-only file system)
Even, if the file is read only, why I can't read it? I really can't understand what is wroong. I have this premission in my manifest:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
Can someone give me a clue? I know that I'm missing something small, but I really can't spot it.
Here is how I write the file:
/* Write content to a file */
private void writeToFile(ArrayList<String> list, Context cont) {
File file = new File("jokesBody1.bjk");
FileOutputStream fos;
if(list != null){
try {
fos = cont.openFileOutput("jokesBody1.bjk", Context.MODE_PRIVATE);
ObjectOutputStream out = new ObjectOutputStream(fos);
out.writeObject(list);
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}else{
try {
file.createNewFile();
fos = openFileOutput("jokesBody1.bjk",Context.MODE_PRIVATE);
ObjectOutputStream out = new ObjectOutputStream(fos);
out.writeObject("");
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
You are trying to create the file, which of course fails on a read-only file.
Remove this line:
file.createNewFile();
This is usually used to create a new empty file before writing to it. You really don't need it if you just want to read a file that already exists.
EDIT:
Just use this:
ObjectInputStream ois = new ObjectInputStream( context.openFileInput("jokesBody1.bjk"));
Of course, you'll also have to pass a Context to the function.
You can only use File with a full path. For accessing your private files, use Context, just as you do when saving the file.
Your full function should look like:
private ArrayList<String> readFromFile(Context context) {
ArrayList<String> list = new ArrayList<String>();
try {
ObjectInputStream ois = new ObjectInputStream( context.openFileInput("jokesBody1.bjk"));
try {
list = (ArrayList)ois.readObject();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
ois.close();
} catch (IOException e) {
Log.e("log activity", "Can not read file: " + e.toString());
}
return list;
}
You aren't specifying any path:
File file = new File("jokesBody1.bjk");
So, you are not saying the app WHERE to look for the file.
Maybe, you want to search it here?
Environment.getExternalStorageDirectory()
I have the below 2 methods, supposed to read and write to a file:
/* Write content to a file */
private void writeToFile(ArrayList<String> list) {
#SuppressWarnings("unused")
File file = new File("jokesBody1.bjk");
FileOutputStream fos;
if(list != null){
try {
fos = openFileOutput("jokesBody1.bjk",Context.MODE_PRIVATE);
ObjectOutputStream out = new ObjectOutputStream(fos);
out.writeObject(list);
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}else{
try {
fos = openFileOutput("jokesBody1.bjk",Context.MODE_PRIVATE);
ObjectOutputStream out = new ObjectOutputStream(fos);
out.writeObject("");
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/* Read file's content */
private ArrayList<String> readFromFile() {
File file = new File("jokesBody1.bjk");
ArrayList<String> list = new ArrayList<String>();
try {
ObjectInputStream ois = new ObjectInputStream( new FileInputStream( file ) );
try {
list = (ArrayList)ois.readObject();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
ois.close();
} catch (IOException e) {
Log.e("log activity", "Can not read file: " + e.toString());
}
return list;
}
When I'm calling the above methods I'm getting this error:
02-15 10:28:48.165: E/log activity(1743): Can not read file: java.io.FileNotFoundException: /jokesBody1.bjk: open failed: ENOENT (No such file or directory)
Ok, it clearly says that the file is not there, but, isn't this code supposed to create it:
File file = new File("jokesBody1.bjk");
Why I'm getting this error? I know that I'm missing something small - probably a piece of code that creates the file(I'm not sure), but as a beginner, I'm not able to spot the issue.
File file = new File("jokesBody1.bjk");
Just creates a File objects that points to that path, but no actual file.
Use
file.createNewFile();
To actually create the file.
Ok, it clearly says that the file is not there, but, isn't this code supposed to create it:
Actually, no. It only creates a File object, an then java assumes that file to exist.