I'm making a program that opens a previous saved file through serialization and want to create a new one, however, data stays in.
How can I make the program forget the data?
If you specify an attribute with the keyword transient, then it will not be serialized. If you're saving the data by serializing objects and writing them to files, this may be what you're looking for. Here's an example of using the transient keyword.
Shouldn't creating a new instance of whichever class you are serializing give you such an 'empty data record'?
Using the example of a text editor you use, you would have, say, a Document class which completely encapsulates a text document and assume you use serialization to save it, then simply new Document() would give you an empty document... Until you fill in some text (or data in your program) you shouldnt open a file...
Assuming you meant a tree of Employee data, or a tree data structure with Employee objects at its nodes, then creating a new such tree will give you what you want.
Think, how did you create the first data set that you serialized? Just repeat that process...
Related
I have different JSON files and need to read, process and write the containing JSON objects of a JSON array.
The output format (more specific: the output class) is for all files the same. Lets call it OutputClass. Hence the item processor is something like ItemProcessor<X, OutPutClass>. Where X is the class of the specific JSON file.
The difference between files are:
The JSON array / the information is at a different position in every JSON file
The structure of the JSON objects in the JSON array are different (the objects in file a have a different syntax than the ones in file b)
I already came across of #StepScope and was able to dynamically generate a reader (depending on job parameters) which starts reading at a different position in the JSON structure.
But I have no idea how to dynamically choose an ItemProcessor depending on the job parameters. Because I got many different JSON files and want to reduce the amount of code to write for each file.
Since you were able to create a dynamic item reader based on job parameters by using the a step-scoped bean (which is the way I would do it too), you can use the same approach to create a dynamic item processor as well.
I am trying to recall a list of employees from an array in Java. I can either choose to do them individually via their ID number or bring all employee info up at once. I know how to code everything else but I cannot find a clear tutorial on how to recall the data and project it onto the text box I have programmed into my GUI. I have the array already created in a different class but I need to get the information from that one and display it in the GUI. Any help would be appreciated. Thanks.
If you want more info just let me know.
[The image is a screenshot of the simple GUI I made.]
There are many ways to do this, but one simple way that may help you to understand this process is as follows:
Implement a store method that simply writes all data to a file in a format of your choice. XML is common, as is TSV or CSV. Some of those are very easy to use, as predefined classes exist to handle them partially or completely.
You will have to read the data you want to store from whereever you have it in your application, possibly in the text boxes directly.
Accordingly implement a restore method that reads the file and fills it back into your data structure and/or the text boxes.
What is difference between serialization and database storage In java? Doesnt serialization actually mean storing data in a database on server?
Let's think of the database like a bowl.
If you want to keep stuff from going everywhere, you put it in the bowl.
Your stuff is the data you want to store. Right now it's out there, on the table, in a box.
So we're going to take the stuff out of that box. The problem is, the stuff in our box probably won't fit into the bowl. How do we fix that?
We need to change it into the type of object that will fit into our bowl. We need to serialize it.
Our serialized data will fit in the bowl now. So we take our serialized data and we pour it into the bowl, and we have the most important meal of the day.
In case this was all really complicated. Simplified: to serialize is to change, and a database is a place to store stuff. Often, you change stuff before you store it.
Serialization can be used to prepare an object for database storage - it is a the process of converting an object into a storable or transmittable format, such as a string or a stream of bytes.
We can't store a java object into most normal storage types as-is - but if we for instance serialize it into JSON we can store it. We can then retrieve the JSON at a later point from the storage and deserialize it to get back an object the same as our original object, given that the serialization and deserialization is properly implemented.
Of course, this doesn't have to entail database storage - having the object serialized into a JSON stream for instance also allows us to transmit it over the internet to be deserialized on another computer.
No. Not at all. Serialization in Java is an API which generates a storeable version of an object that you can later load back from disk (or wherever you store it) and make it back into an object with (hopefully!) the same state as it once had. There are alternatives to it such as Google Protobufs which are better for networked applications, but it is good enough for most simple uses.
Serialization is the process of converting a data structure into a form that can be persisted (saved on a hard drive) in any way. It can be binary, xml, plain text, html, ... usually the goal is to be able to deserialize, that is restore back the state of your data structure at the time it was persisted.
A database is just the place (and not the way) where you store your data.
I have a standard program with a list of interview questions that people use when interviewing new members. The questions are hard coded, the interviewer records the answer to the questions. The answers when submitted are added to an object (called iQuestions) and then stored in a .txt file on the server. Well times change and now we want to add additional questions to the list, which is easy enough to do, however when I change the iQuestions in both the server and client, the old records bomb out with a "serialized object" error (the object saved is not the same as the object in the program that I am trying to get from. What is the easiest way to get past this?
This is where not having the static serialVersionUID defined in a Serializable class can burn you later. As you state, your new version of the serializable class is different than the one that was used to save off data and as such the "automatic" deserialization cannot determine how to read the data back in to your new version of the class ( http://www.javapractices.com/topic/TopicAction.do?Id=45 ). If you still have access to the original iQuestions class, you might consider writing a converter that deserializes the questions using the original class and then write out the relevant data into another format (perhaps using a database to store the questions would be more reliable and easier to update or storing as JSON in a text file for simplicity?).
I am developing a program which has three JTextBox which my users can enter and check some text for right rule.
So I want add a ablitiy to my program that my users can add or remove their favorite text to a Favorite List and can create folder in Favorite list and put some text in it, such as Bookmark library in FireFox or other web browser.
I want use RandomAccessFile to save favorite list as a favorite source.
How do I implemet it? is there beter way to implement it? is there beter way from RandomAccessFile?
Can any one help me?
Thanks.
There could be lots of approaches. It all depends on what you want to achieve.
Consider using Java serialization mechanism. You can serialize a collection of bookmarks to a file. When your app starts, you deserialize it, and get the same collection data.
The advantages are: simple and easy implementation. The disadvantages: you can't look through stored bookmarks in a text editor or something. The same class hierarchy is to be used to load the serialized version.
XML is human-readable and provides easy interoperability. Other applications would be able to handle your list of bookmarks.
It usually takes more resources to parse the XML and load it to memory and then to create the internal object structures. Though you can use the DOM to traverse the tree all the time, it could be not as convenient as the internal data structure using specialized classes.
Random Access Files work best with fixed record sizes. It means all the fields of your bookmarks must be fixed-length. For example, the name of a bookmark is String. When you write it out to a file, you store it like an array of a fixed length, let's say 20. This automatically implies that if users give a bookmark the name which length is greater than 20, the remaining characters would be lost.
It is also easy to implement with the caveats above. Of course the records could be of variable length, but then you lose the random access to file because you cannot easily calculate the position of a specific record.
Firefox uses JSON for storing bookmarks and allows exporting to HTML. You can explore this too.
You can also store bookmarks, and things you want to keep between sessions in the Preferences,
see http://download.oracle.com/javase/6/docs/api/java/util/prefs/Preferences.html