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Thread: ObjectInputStream

  1. #1
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    Default ObjectInputStream

    Hello,

    i have saved an arrayList to file using the ObjectOutputStream but now when i try to read the file i get problems.

    saveOnFile:
    public void saveOnFile() {
    		try {
    			ObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("object.txt"));
    			output.writeObject(mediaList);
    			output.close();
    		} catch(Exception ex) {
    			ex.printStackTrace();
    		}
    	}

    readFromFile:
    public void readFromFile() {
    		try {
    			ObjectInputStream inStream = new ObjectInputStream(new FileInputStream("object.txt"));
    			this.mediaList.add( (Media) inStream.readObject());
    			inStream.close();
    		} catch(Exception ex) {
    			ex.printStackTrace();
    		}
    	}

    Does it know which instance the object is or do i need to handle this?

    ERRORS:
    java.lang.ClassCastException: java.util.ArrayList cannot be cast to project.Media
    	at project.MediaHandler.readFromFile(MediaHandler.java:66)
    	at project.Window.<init>(Window.java:73)
    	at project.Window.main(Window.java:199)

    ED, my classes are serializable.
    Last edited by sebbe605; April 9th, 2014 at 03:59 PM.


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: ObjectInputStream

    ArrayList cannot be cast to project.Media
    The code reads an ArrayList object and tries to cast it to a Media object?
    Did you try to cast it to an ArrayList?
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: ObjectInputStream

    I tried with this earlier:
    	public void readFromFile() {
    		try {
    			ObjectInputStream inStream = new ObjectInputStream(new FileInputStream("object.txt"));
    			this.mediaList.addAll( (ArrayList<Media>) inStream.readObject());
    			inStream.close();
    		} catch(Exception ex) {
    			ex.printStackTrace();
    		}
    	}

    It doesn't do anything during execution and gives me warning
    Type safety: Unchecked cast from Object to ArrayList<Media>
    Last edited by sebbe605; April 9th, 2014 at 04:34 PM.

  4. #4
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    Default Re: ObjectInputStream

    What warning? Post the full text.

    Try testing by reading into an ArrayList variable and printing out the contents.

    The code works for me.
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: ObjectInputStream

    This warning: Type safety: Unchecked cast from Object to ArrayList<Media>

  6. #6
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    Default Re: ObjectInputStream

    Okay, i changed some stuff around and i think that this should work, but it doesn't work.

    	public void readFromFile() {
    		  try {  
    			  ObjectInputStream inStream = new ObjectInputStream(new FileInputStream("object.txt"));
    		   try {
    		    ArrayList<Media> mediaList = (ArrayList<Media>) inStream.readObject(); 
    		    } catch (EOFException exc) {
     
    		    }
    		    inStream.close();
    		  } catch(Exception ex) {
    		   ex.printStackTrace();
    		  }
    		}

  7. #7
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    Default Re: ObjectInputStream

    it doesn't work.
    Please explain.
    If you don't understand my answer, don't ignore it, ask a question.

  8. #8
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    Default Re: ObjectInputStream

    Couldn't get it to work so i went with another method.

    	public void saveOnFile() {
    		File file = new File("data.txt");
     
    		try {
    			if(!file.createNewFile()) {
    				file.createNewFile();
    			}
    			FileWriter out = new FileWriter(file.getAbsoluteFile());
    			BufferedWriter bW=new BufferedWriter(out);
     
    			bW.write(this.mediaList.size() + "\r\n");
    			for(int i = 0; i < mediaList.size(); i++) {
    				 bW.write(this.mediaList.get(i).toString());
    			}
    			bW.close();
    		} catch(IOException e) {
    			e.printStackTrace();
    		}
    	}
     
    	public void readFromFile() {
    		FileReader fileReider;
    		try {
    			fileReider = new FileReader("data.txt");
    			BufferedReader bufferedReader = new BufferedReader(fileReider);
    			int tempSize = Integer.parseInt(bufferedReader.readLine());
     
    			for(int i = 0; i < tempSize; i++) {
    				// Get items from file
    				String title = bufferedReader.readLine();
    				Double playTime = Double.parseDouble(bufferedReader.readLine());
    				int year = Integer.parseInt(bufferedReader.readLine());
    				bufferedReader.readLine();
    				String directory = bufferedReader.readLine();
    				String mediaPath = bufferedReader.readLine();
    				String imagePath = bufferedReader.readLine();
    				bufferedReader.readLine();
    				int objectTypeValue = Integer.parseInt(bufferedReader.readLine());
     
    				if(objectTypeValue == 0) { // If Movie add movie else add a TV-show
    					String quality = bufferedReader.readLine();
    					boolean subtitles = Boolean.parseBoolean(bufferedReader.readLine());
    					String language = bufferedReader.readLine();
    					String writer = bufferedReader.readLine();
     
    					addMovie(title, playTime, year, directory, mediaPath, imagePath, quality, subtitles, language, writer);
    				} else {
    					int season = Integer.parseInt(bufferedReader.readLine());
    					int episode = Integer.parseInt(bufferedReader.readLine());
     
    					addTVShow(title, playTime, year, directory, mediaPath, imagePath, season, episode);
    				}
    			}
    			bufferedReader.close();
    		} catch (FileNotFoundException e) {
    			e.printStackTrace();
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    	}

    This is the way i learned to do it in c++ thought it would be nice to know how ObjectInput-/output-Stream works as well.

  9. #9
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    Default Re: ObjectInputStream

    I got it to work as I stated in post#4. I don't know what you did that kept it from working.
    If you don't understand my answer, don't ignore it, ask a question.

  10. #10
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    Default Re: ObjectInputStream

    Neither do i. I was looking at another thread there someone had similar problems. They ended up changing the ArrayList to List
      List<Media> mediaList = (List<Media>) inStream.readObject();
    but he only had one type of element and i have two. But the way i did it know is easier to understand because i can see every step in the function because i made it myself. I find that thats a problem with "premade" methods "it's hard to get an understanding of what's actually happening".