How to write object in file in java without using object serialization? - blackberry

I want to write object to file. But as per my study I found that it is not possible without object serialization. Other way is to convert object to array of bytes and then to write to file. But for this also object serialization is required. Is there any other way to write object to file? Because I want to use the same code in android and blackberry also. Please help me, I want to solve this problem as early as possible. Thanks in advance.


If you want to write an object to a file, then you by definition want to serialize it - that's what serialization means. If you're just looking for a way to save data to a file that doesn't rely on device-specific storage mechanisms, then you will need to write some custom serialization code. For every class that you want to store in a file, you'll need to do the following:
Write a method that stores the current state of the object in some writable structure, such as a string or byte array
Write a method that converts the string or byte array back into an object (it will probably be easiest to have this method take a stream as a parameter, and have it create a new object based on the data in that stream)
For example, you could save objects as XML or JSON strings, or in more efficient means - the best way to store it mainly depends on what sort of data you are storing and what you need to do with it.
It is good practice when doing this to include some version number that defines what version of the class you are using, and include this first when serializing the object. That way, when you deserialize, you can check that version number and know how it was serialized. This makes it easy to change your serialization scheme later on while still maintaining backwards compatibility with older files.
If you are just looking for a general purpose storage mechanism that is device-independent, then you could also look into using a SQLite database - they are supported on most if not all modern mobile operating systems. This will be easier than hand-rolling your own serialization, and will also generally have better performance.

Related

Genexus Extensions SDK - Is there a built in helper to save data locally?

I Would like to know if the Genexus Extension SDK already implements something to store persistent data locally (KB Independant and per KB), something like PersistentDictionary from ManagedEsent
I know that genexus uses SQL Server to store KB Related information, is there an interface for me to extend that?
I want to save data per genexus instance (locally) and use that data to load my extension config, everytime the users executes Genexus.

We don't use PersistentDictionary. I would advice not to use it, as it's a Windows specific API, and we are trying make everything new cross platform, as part of our journey of making GeneXus BL run on other OS.
There are different options of persistence, depending on the specific details of your scenario.
If you want to store something like configuration settings for your extension, you can use the ConfigurationHelper class located in Artech.Common.Helpers. This class provides read access to the configurations defined in the GeneXus.exe.config file in the GeneXus installation folder, as well as read/write access to the Environment.config file located in %AppData%\GeneXus\GeneXus\<version>\Environment.config. Note this file depends on the current user, and is shared between different GeneXus instances of a same main version.
The ConfigurationHelper class provides operations to read and save settings of basic types string, int and bool.
const string MY_EXTENSION = "MyExtensionSettings";
const string SETTING1 = "Setting1";
const string SETTING1_DEFAULT_VALUE = "This is the default value";
const string SETTING2 = "Setting2";
const int SETTING2_DEFAULT_VALUE = 20;
string setting1Value = ConfigurationHelper.GetUserSetting(MY_EXTENSION, SETTING1, SETTING1_DEFAULT_VALUE);
int setting2Value = ConfigurationHelper.GetUserSetting(MY_EXTENSION, SETTING2, SETTING2_DEFAULT_VALUE);
// Do something and maybe change the setting values
ConfigurationHelper.SetUserSetting(MY_EXTENSION, SETTING1, setting1Value);
ConfigurationHelper.SetUserSetting(MY_EXTENSION, SETTING2, setting2Value);
If you want to store something in a file based on the current opened KB, there's no specific API that'll help you handle the persistence. You can use the properties Location and UserDirectory of the KnowledgeBase class to access the KB location or a directory for the current user under the KB location, but it's up to you the handling of the file. You'll have to decide on the file format (binary or text), file encoding in case of text files, and handle all read and write operations to that file.
We use the kb.UserDirectory path to store non-critical stuff, such as the set of objects that were opened the last time the KB was closed, or the filter values for different dialogs.
In case you'd like to store settings inside the KB, there are plenty of options.
You can add properties to existing objects, KB version or environment. Making it a property doesn't necessary mean you'll have to edit the value in the property grid, although it's usually the way to go.
You can define a new kind of entity. Entities are the basic elements that can be stored in a KB. The entity may be stored depending on the active version of the KB, or may be independent of the current version. Entities can have properties, whose serialization is handled by the property engine, and also can read and store a byte array whose format and content will be handled by you.
You can add a part to an existing object. For instance you may want to add a part to Procedure objects. In order to do this you'll have to extend KBObjectPart, define your part in a BL package, declare that the part composes objects of certain type, and provide an editor for your new part in a UI package. KBObjectPart extends Entity so the serialization of the part is similar as in the previous case. A caveat of this option is that you'll also have to handle how the part content is imported, exported, and compared.
You can add a new kind of object. Objects extend the KBObject class, which extends Entity. Objects are not obliged to have parts (for instance the Folder object doesn't have any). When choosing to provide a new kind of object you have to consider a couple of things, such as:
Do you want to be able to create new instances from the new object dialog?
Will it be shown in the folder view?
Can it be added into modules?
Can it have the same name as other objects of different types?
As a general guideline, if you choose to add a new property, add it to objects, versions, or environments, not parts. Adding properties to parts is not so good for discoverability. Also if you choose to add a new kind of object, even though it inherits from Entity which as mentioned earlier can read and store a byte array, it's preferred to don't use the byte array in KBObject and add a KBObjectPart to it instead. That way the KBObject remains as lightweight as possible, and loading the object definition from the DB remains fast, and the blob content is loaded only when truly needed.
There's no rule of thumb. Depending on the specifics of the scenario, one option may be more suited than others.

Do I have to deserialize the whole complex json file (with many nested arrays and objects) when I need only one object? Flutter, Dart

https://github.com/enter link description herePoojaB26/ParsingJSON-Flutter/blob/master/assets/page.json

That's a tiny JSON file and there is no reason for premature optimizations.
Just deserialize it and then access the items of the generated Dart data structures to get what you need. Everything else is probably equally expensive and won't buy you anything.

What's the simplest way to encode a chosen 'root' Core Data entity together with all of its relationships?

I use Core Data within my iOS 7 app to handle the editing and creation of entities. The entities have relationships between them, which all have inverses (as Apple advises).
For the sake of this question, let's pick any one of these interrelated entities and call it the Root entity: the thing that I want to encode with; the thing that logically lives on the 'top' of the hierarchy. I will call this the 'object graph'.
The question is:
What's the easiest way of encoding and decoding such an object graph to and from NSData?
The reason I want to do this is that I'd like my Core Data object graph to be persisted onto a cloud service, without the need of writing my own NSIncrementalStore subclass (it's a bit involved...!).
AutoCoding together with HRCoder almost looks like it could do the job, but I've experimented with this combination and it doesn't quite work with NSManagedObjects at the time of writing.
Still, I'm seeking alternatives. There can't only be one way to do this, surely.
It doesn't have to be JSON, but it'd be nice. Binary would be fine.

It seems to me you do not need to subclass NSIncrementalStore. You can create records and save them to your store with a plain vanilla store created via addPersistentStoreWithType:... with a NSPersistentStoreCoordinator.
The straight-forward way is to handle the incoming JSON by simply taking the data and copying it to the properties of your NSManagedObject subclasses, like this:
object.title = jsonDictionary[#"title"];
object.numericAttribute = [jsonDictionary[#"numericAttribute] integerValue];
If you take care about naming the attribute and entity names exactly the same you can maybe use some shortcuts using KVC, like
[object setValue:jsonDictionary[key] forKey:key];
I once did the above for a large legacy project where it was not feasible to repeat the old attribute names, so I used a custom property list (plist) to match around 800 attribute names.

What data type should I use to store a GUID in Core Data?

I'm going to be generating CFUUID objects (if there's a better way to create a GUID on iOS, let me know) that need to be persisted using Core Data. There is no GUID data type in Core Data. What's the preferred type? It looks like CFUUID objects easily convert to and from a string, so I'm thinking that. Another option might be Binary Data.
Another consideration is that these GUIDs will going into and coming out of JSON objects (using built-in iOS5 JSON Serialization via NSJSONSerialization).

If I were doing it, I would just store it as a string.
You could store it as binary data, but since it's going to be going into and coming out of a string (which is what JSON is represented with) it's probably easier to store it as a string and not worry about converting it backwards and forwards.

iPhone json library to map the json to my own objects

I seek a iPhone json library that parse json strings into Custom Objects (such as Employee, Course, etc, not into NSDictionary or NSArray)
Thanks.

I don't think one exists. How would you design a general one, without knowing in advance about the kinds of objects that you'll need to parse into? And more critically, JSON is only designed to encode basic data types; it is not intended to be a full object serialization framework (those are usually language specific or have language-specific bindings). However, it should be very easy to write a converter to your custom objects.

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