Serialization and Data Structures

Hi all I need an advice. I'll explain my problem. I want take data from web , elaborate the result, keep it and serialize on file. I need to restore and use data from file , somehow. I dont want that file is been overwritten and lose old data.I need have a sort of list of Object in the File where i can search the last , use Method of another class to find some values etc , insert or similar, etc.....

In this case i used ArrayList but i dont know if it was the best choise. I tried to do this but i have a problem know. In the specific if use a Class called Data and i want a serilizate file that keep ArrayList. So when i call method save(Object obj) of FileStructureClass(a class that i made to save, load file ) in this method i need to check if file already has an ArrayList so if it's true i can add in that Arraylist the Object , passed as parameter , else i return a new ArrayList. Of course i do a cast from Object to Data Class when i add开发者_运维知识库 in ArrayList. I would fix this problem and then after find a better solution (if there is) to my problem. The Data Class contains only 3 String and 1 GregoriusCalendar. Keep in mind(for the choise as ArrayList as Solution) that i need save file 1 time at day(i do a check with last element of the arraylist and do check with actual GregoriusCalendar..if past 1 day i can insert the element in arraylist). After Explain the situation i list my problems

1. When i try to save for the FIRST time a Data Object in the Arraylist i have an error java.io.EOFException , i think that the problem is in tmp= ArrayList)ois.readObject(); but i cant find a solution. Dont happen when i insert manually a DataObject in the ArrayList and i use a method to insert a second one
2. According to you , ArrayList is a valid solution for my situation?

This method check if the file has data or not. If it's empty i create a new one ArrayList and return it otherwise i read the ArrayList already store in the file , and i return it

public ArrayList<Dati> check() {
    ArrayList<Dati> tmp = new ArrayList<Dati>();    
    ObjectInputStream ois;
    try{                        
        fileInput = new FileInputStream("prova.dat");           
        ois = new ObjectInputStream(fileInput);         
        if (ois.readObject() == null) {
            Logger.getLogger("file is empty");
            ois.close();
            return tmp;         
        }
        //The error that i recive arrives from the under line 
        //  (Impossible load file check method: java.io.EOFException
        tmp = (ArrayList<Dati>) ois.readObject();           
        ois.close();
    } catch (IOException e) {
        System.out.println("Impossibile caricare i dati metodo check: "+e);
    }
    catch (ClassNotFoundException e) {
        System.err.println("error");
    }       
    return tmp;
}

//This method recive data of file that contains ArrayList<Data>
// and add to this a Data Object gave as Parameter
public void save(Object obj){

    try{        
        ArrayList<Data> temp = check();     
        temp.add((Data) obj);
        ObjectOutputStream os = 
            new ObjectOutputStream(new FileOutputStream("prova.dat"));
        os.writeObject(temp);
        os.flush();
        os.close();
    }
    catch(IOException e){
        System.out.println("Impossible save datas: "+e);
    }
}

public Object load(String path){
    Object obj=null;
    try{            
        fileInput=new FileInputStream(path);
        ois=new ObjectInputStream(fileInput);
        obj=ois.readObject();
        ois.close();
    }
    catch(IOException e){
         System.out.println("Impossible load file: "+e);
    }
    catch(ClassNotFoundException e){
         System.err.println();
    }
    return obj;
}

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1. When i try to save for the FIRST time a Data Object in the Arraylist i have an error java.io.EOFException , i think that the problem is in tmp= (ArrayList)ois.readObject(); but i cant find a solution. Dont happen when i insert manually a DataObject in the ArrayList and i use a method to insert a second one

This seems to be correct. Looking at javadoc, it does seem like ois.readObject() returns null when there is nothing in the file. One approach I can think of is to initialize the file with an empty ArrayList in setup phase.

1. According to you , ArrayList is a valid solution for my situation?

I don't see why not. But it depends on what you will do with the list after reading it. If you have to search it often and it is large then you may consider a different data structure.