i need to save data from an java desktop application. The main part of the Data are the texts of around 50 labels. Which are spread over 5 Java GUI-classes. The Rest are some simple application settings.
Now i am quit unsure about how to safe these data. A friend told me to use Random access Data and to write some kind of "serializable" object. At the moment i am using a .txt and a fileReader/writer. But this seemes impractical for 50-100 Data if your want to search the position in the .txt by every update. This is my same problem with random access data.
i thought about using some kind of embedded DB like "h2" but i dont now if this is to much and too complicated for such a small programm.
An other question is how do i put the text of all labels at the programm start. one way i am thinking about is to have a big list of all labels with determind positions and after reading the data from whatever to go over this list and set the labes. An other way would be to give every Label an id.
But maybe there is a much better way. But i dont now how to access the labels by names read from the data.
For saving serializable objects. Can i safe all the gui-object or do i need to combine se data in one class?
maybe someone could give a nice advise =)
For such a small number of labels, I would just keep all data in memory. On app initialization load the file and on every edit write the entire file from scratch
(If you are concerned about reliability in the face of power loss and random crashes during write you need to be careful here. For example, write the new data to a different file, fsync() then atomically rename the new file to the desired filename.)
I'm not sure I understand your serialization problem -- but it seems like you have some sort of language translation layer that tells the gui elements what to display. If so, then yes - I would store the labels in a central class (say LablesMap) and have the other classes refer to data in that class using some constant keys. E.g.,
myButton.setText(labelsMap.get(CANCEL_BUTTON_LABEL)
where CANCEL_BUTTON_LABEL is some constant or enum value.
I fear I may not be truly understanding the utility of database software like MySQL, so perhaps this is an easy question to answer.
I'm writing a program that stores and accesses a bestiary for use in the program. It is a stand-alone application, meaning that it will not connect to the internet or a database (which I am under the impression requires a connection to a server). Currently, I have an enormous .txt file that it parses via a simple pattern (Habitat is on every tenth line, starting with the seventh; name is on every tenth line, starting with the first; etc.) This is prone to parsing errors (problems with reading data that is unrecognizable with the specified encoding, as a lot of the data is copy/pasted by lazy data-entry-ists) and I just feel that parsing a giant .txt file every time I want data is horribly inefficient. Plus, I've never seen a deployed program that had a .txt laying around called "All of our important data.txt".
Are databases the answer? Can they be used simply in basic applications like this one? Writing a class for each animal seems silly. I've heard XML can help, too - but I know virtually nothing about it except that its a mark-up language.
In summary, I just don't know how to store large amounts of data within an application. A good analogy would be: How would you store data for a dictionary/encyclopedia application?
So you are saying that a standalone application without internet access cannot have a database connection? Well your Basic assumption that DB cannot exist in standalone apps is wrong. Today's web applications use Browser assisted SQL databases to store data. All you need is to experiment rather than speculate. If you need direction, start with light weight SQLite
While databases are undoubtedly a good idea for the kind of application you're describing, I'll throw another suggestion your way, which might suit you if your data doesn't necessarily need to change at all, and there's not a "huge" amount of it.
Java provides the ability to serialise objects, which you could use to persist and retrieve object instance data directly to/from files. Using this simple approach, you could:
Write code to parse your text file into a collection of serialisable application-specific object instances;
Serialise these instances to some file(s) which form part of your application;
De-serialise the objects into memory every time the application is run;
Write your own Java code to search and retrieve data from these objects yourself, for example using ordered collection structures with custom comparators.
This approach may suffice if you:
Don't expect your data to change;
Do expect it to always fit within memory on the JVMs you're expecting the application will be run on;
Don't require sophisticated querying abilities.
Even if one or more of the above things do not hold, it may still suit you to try this approach, so that your next step could be to use a so-called object-relational mapping tool like Hibernate or Castor to persist your serialisable data not in a file, but a database (XML or relational). From there, you can use the power of some database to maintain and query your data.
I am writing a program in Java which tracks data about baseball cards. I am trying to decide how to store the data persistently. I have been leaning towards storing the data in an XML file, but I am unfamiliar with XML APIs. (I have read some online tutorials and started experimenting with the classes in the javax.xml hierarchy.)
The software has to major use cases: the user will be able to add cards and search for cards.
When the user adds a card, I would like to immediately commit the data to the persistant storage. Does the standard API allow me to insert data in a random-access way (or even appending might be okay).
When the user searches for cards (for example, by a player's name), I would like to load a list from the storage without necessarily loading the whole file.
My biggest concern is that I need to store data for a large number of unique cards (in the neighborhood of thousands, possibly more). I don't want to store a list of all the cards in memory while the program is open. I haven't run any tests, but I believe that I could easily hit memory constraints.
XML might not be the best solution. However, I want to make it as simple as possible to install, so I am trying to avoid a full-blown database with JDBC or any third-party libraries.
So I guess I'm asking if I'm heading in the right direction and if so, where can I look to learn more about using XML in the way I want. If not, does anyone have suggestions about what other types of storage I could use to accomplish this task?
While I would certainly not discourage the use of XML, it does have some draw backs in your context.
"Does the standard API allow me to insert data in a random-access way"
Yes, in memory. You will have to save the entire model back to file though.
"When the user searches for cards (for example, by a player's name), I would like to load a list from the storage without necessarily loading the whole file"
Unless you're expected multiple users to be reading/writing the file, I'd probably pull the entire file/model into memory at load and keep it there until you want to save (doing periodical writes the background is still a good idea)
I don't want to store a list of all the cards in memory while the program is open. I haven't run any tests, but I believe that I could easily hit memory constraints
That would be my concern to. However, you could use a SAX parser to read the file into a custom model. This would reduce the memory overhead (as DOM parsers can be a little greedy with memory)
"However, I want to make it as simple as possible to install, so I am trying to avoid a full-blown database with JDBC"
I'd do some more research in this area. I (personally) use H2 and HSQLDB a lot for storage of large amount of data. These are small, personal database systems that don't require any additional installation (a Jar file linked to the program) or special server/services.
They make it really easy to build complex searches across the datastore that you would otherwise need to create yourself.
If you were to use XML, I would probably do one of three things
1 - If you're going to maintain the XML document in memory, I'd get familiar with XPath
(simple tutorial & Java's API) for searching.
2 - I'd create a "model" of the data using Objects to represent the various nodes, reading it in using a SAX. Writing may be a little more tricky.
3 - Use a simple SQL DB (and Object model) - it will simply the overall process (IMHO)
Additional
As if I hadn't dumped enough on you ;)
If you really want to XML (and again, I wouldn't discourage you from it), you might consider having a look a XML database style solution
Apache Xindice (apparently retired)
Or you could have a look at some other people think
Use XML as database in Java
Java: XML into a Database, whats the simplest way?
For example ;)
Goodevening Sir/Mam,
I am trying to make a small program that will be used for hotel room reservation, please tell me how to store the data of room's status on disk, as when we open the program next time we'll get the data.
Please help i am very new here.
Have a nice day!
It would probably be the best to serialize it.
One way to do this is serialize the array write it to a file. java-serialization has an example for serializing an object to a .txt file; you can adapt this code to serialize an array.
The usual way of doing this in Java is to serialize the data structure / class. It's normally pretty easy to do as you just extend Serializable in the appropriate class.
Before you leap into implementing a hotel reservation system based on writing stuff into files, you need to consider using a relational database instead. A decent RDB will give better performance AND you won't have to worry about your program crashing with unsaved updates ... or (worse still) in the middle of writing the updates to disk.
The fact you are asking this question suggests (to me) that you are short on knowledge and experience. If this is a real project for a real hotel, stop now before someone gets hurt! (But if this is a student project, feel free to continue, and learn. But I still think a proper database is the right way to go ...)
I have read quite a number of articles on Serialization and how it is so nice and great but none of the arguments were convincing enough. I am wondering if someone can really tell me what is it that we can really achieve by serializing a class?
Let's define serialization first, then we can talk about why it's so useful.
Serialization is simply turning an existing object into a byte array. This byte array represents the class of the object, the version of the object, and the internal state of the object. This byte array can then be used between JVM's running the same code to transmit/read the object.
Why would we want to do this?
There are several reasons:
Communication: If you have two machines that are running the same code, and they need to communicate, an easy way is for one machine to build an object with information that it would like to transmit, and then serialize that object to the other machine. It's not the best method for communication, but it gets the job done.
Persistence: If you want to store the state of a particular operation in a database, it can be easily serialized to a byte array, and stored in the database for later retrieval.
Deep Copy: If you need an exact replica of an Object, and don't want to go to the trouble of writing your own specialized clone() class, simply serializing the object to a byte array, and then de-serializing it to another object achieves this goal.
Caching: Really just an application of the above, but sometimes an object takes 10 minutes to build, but would only take 10 seconds to de-serialize. So, rather than hold onto the giant object in memory, just cache it out to a file via serialization, and read it in later when it's needed.
Cross JVM Synchronization: Serialization works across different JVMs that may be running on different architectures.
While you're running your application, all of its objects are stored in memory (RAM). When you exit, that memory gets reclaimed by the operating system, and your program essentially 'forgets' everything that happened while it was running. Serialization remedies this by letting your application save objects to disk so it can read them back the next time it starts. If your application is going to provide any way of saving/sharing a previous state, you'll need some form of serialization.
I can share my story and I hope it will give some ideas why serialization is necessary. However, the answers to your question are already remarkably detail.
I had several projects that need to load and read a bunch of text files. The files contained stop words, biomedical verbs, biomedical abbreviations, words semantically connected to each other, etc. The contents of these files are simple: words!
Now for each project, I needed to read the words from each of these files and put them into different arrays; as the contents of the file never changed, it became a common, however redundant, task after the first project.
So, what I did is that I created one object to read each of these files and to populate individual arrays (instance variables of the objects). Then I serialized the objects and then for the later projects, I simply deserialized them. I didn't have to read the files and populate the arrays again and again.
In essense:
Serialization is the process of
converting a set of object instances
that contain references to each other
into a linear stream of bytes, which
can then be sent through a socket,
stored to a file, or simply
manipulated as a stream of data
See uses from Wiki:
Serialization has a number of advantages. It provides:
a method of persisting objects which
is more convenient than writing
their properties to a text file on
disk, and re-assembling them by
reading this back in.
a method of
issuing remote procedure calls,
e.g., as in SOAP
a method for
distributing objects, especially in
software componentry such as COM,
CORBA, etc.
a method for detecting
changes in time-varying data.
The most obvious is that you can transmit the serialized class over a network,
and the recepient can construct a duplicate of the original instanstance. Likewise,
you can save a serialized structure to a file system.
Also, note that serialization is recursive, so you can serialize an entire heterogenous
data structure in one swell foop, if desired.
Serialized objects maintain state in space, they can be transferred over the network, file system, etc... and time, they can outlive the JVM that created them.
Sometimes this is useful.
I use serialized objects to standardize the arguments I pass to functions or class constructors. Passing one serialized bean is much cleaner than a long list of arguments. The result is code that is easier to read and debug.
For the simple purpose of learning (notice, I said learning, I did not say best, or even good, but just for the sake of understanding stuff), you could save your data to a text file on the computer, then have a program that reads that info, and based on the file, you could have your program respond differently. If you were more advanced, it wouldn't necessarily have to be a txt file, but something else.
Serializing on the other hand, puts things directly into computer language. It's like you're telling a Spanish computer something in Spanish, rather than telling it something in French, forcing it to learn French, then save things into its native Spanish by translating everything. Not the most tech-intensive answer, I'm just trying to create an understandable example in a common language format.
Serialization is also faster, because in Java, objects are handled on the heap, and take much longer than if they were represented as primitives on the stack. Speed, speed, speed. And less file processing from a programmer point of view.
One of the classical example where serialization is used in daily life is "Save Game" option in any computer games. When player decides save his progress in the game then the application writes the saved state of the game into a file via serialization and when player "Load Game" the serialized file is read and Game state is re-created.