I am developing GWT offline application using HTML5 Local Storage. I would like to cache/store the transfer objects using com.google.gwt.storage.client.Storage (introduced in version 2.3). But the problem is that as for now (version 2.3) the Storage can only save the string values.
Is there any possibility to use GWT's built in rpc serialization/deseralization mechanism from client side code? So that I will be able to serialize transfer objects and store them in Local Storage and retrieve them when needed and deserialize the content.
GWT Docs have this to say:
Local Storage is String Storage
HTML5 local storage saves data in
string form as key-value pairs. If the data you wish to save is not
string data, you are responsible for conversion to and from string
when using LocalStorage. For proxy classes used with the GWT
RequestFactory, you can use RequestFactory#getSerializer() to do
string serializing. For non-proxy objects, you could use JSON
stringify and parse.
EDIT:
RequestFactory#getSerializer() returns an implementation of ProxySerializer. But
ProxySerializer Serializes graphs of EntityProxy objects. A
ProxySerializer is associated with an instance of a ProxyStore when it
is created via RequestFactory.getSerializer(ProxyStore).
So you cannot use it to serialize arbitrary objects. Only EntityProxy objects can be serialized this way. GWT documentation does not mention any method for doing such serialization for non-EntityProxy objects, so I think it is safe to assume that there is no ready-made solution for doing this so far. For non-EntityProxy objects, GWT docs (quoted above) recommend using JSON serialization.
Related
Currently, we are exploring CodeEffects for our one of the rule engine proposal.
We have a dynamic type which is a JSON string. During runtime, we need to apply the rule for JSON using CodeEffects. Is it support for FlexSource or any other possibility.
You need to serialize your Json string into a .NET object, fill it with data if needed, and pass that object to the Evaluator together with your rule for evaluation. The FlexSource is designed specifically to support this kind of scenarios. Download the FlexSource demo project from Code Effects website and replace the XML data file used there as the source object with your Json.
I'm working on my first client-server project and using REST.
So my question is where and how do I handle the data.
Options:
Define a datamodel and share it to the server and client. So I could you use JSON and object transfering, but each change of the datamodel requires also possible changes in the server and client implementation.
Simply transfer the data as basic data types (strings, boolean etc.). So only a datamodel is required in the client.
What do you recommend?
As you want to develop REST APIs and REST evolves around resource representations so first option (define data model) is way to go.
Note that all data model changes will not break the APIs and thus client implementations. Only when you re-structure your resource representation OR you take out one of attribute from model - that's when you will need to version your APIs.
I was looking at using EventStore with SQL Server for the data storage. Most of the performance hit is with SQL Server actually storing the data, and there is a lot of memory allocated in the web server as well.
It turns out it all boils down to the Serialization of the headers (from CommonDomain's EventStoreRepository class) and of the EventMessage (from EventStore).
So I tried to switch from the Binary Serializer to the Protobuf-net one. But the types that need serialization do not have the required attributes to be properly serialized.
Is it possible to use protobuf-net with EventStore + CommonDomain? Has anyone done it?
I am working on a web application which is being developed using GWT. I am also using OWL ontologies and Jena framework to structure semantic contents in the application.
A simple function in the application would be getting some data from the user and send it to the servers side to be stored as a data graph using the ontology. I suppose one way would be to store the data as java class objects equivalent to the ontology classes and send them using the GWT async communication. To convert OWL classes to java, I used Jastor.
My question is that after the server receives the java class, is it possible to easily convert is to an OWL individual and add it to the data graph, using the functions of Jena and/or Jastor? For instance in the server side interface implementation we call something like this:
Public void StoreUser (User userObj) {
//User: a Jastor created java class. userObj is instantiated using the user data on the client side.
OntModel ontModel = ModelFactory.createOntologyModel(OntModelSpec.OWL_DL_MEM);
//Open the ontology here using inputstream and ontModel.read!
Individual indiv = (Individual) userObj.resource();
//Add the individual to the model here! }
Unfortunately I wasn't able to find any Jena function that can add an existing individual to the model.
Would you suggest another way to pass the ontology data to server side and store it, rather than using Jastor created classes (for instance using an XML file)?
Thanks for your help
There are two parts to the answer. First, an Individual is a sub-class of a Jena Resource, which is definitely something that you can add to a model. However, individual resources, or properties or literals are not stored in a Model. A Model stores only triples, represented as Statement objects in the Java API. So to add some resource to a model, you have to include it in a triple.
In Jena, an individual is defined as a subject of a triple whose predicate is rdf:type and whose object is not one of the built-in language classes. So if you have:
ex:my_car rdf:type ex:Ferrari .
ex:Ferrari rdf:type owl:Class .
(note: this example is entirely fictitious!), then ex:my_car would be an individual, but ex:Ferrari would not (because OWL Class is a built-in type). So, to add your individual to your model, you just need to assert that it is of some type. Since I don't know GWT and don't use Jastor, I can't say whether the type association that is normally part of a Jena Individual is retained after serialization. I suspect not, in which case you'll need to have some other means of determining the type of the individual you want to add, or use a different predicate than rdf:type to add the resource to the the Model.
All that said, personally I probably wouldn't solve your problem this way at all. Typically, when I'm working with client-side representations of server-side RDF, I send just the minimal information (e.g. URI and label) to the client as JSON. If I need any more data on a given resource, I either send it along with the initial JSON serialization, or it's just an Ajax call away. But, as I say, I don't use GWT so that advice may not be of any use to you.
I've just started learning Google Web Toolkit and finished writing the Stock Watcher tutorial app.
Is my thinking correct that if one wants to persist a business object (like a Stock) using JDO and send it back and forth to/from the client over RPC then one has to create two separate classes for that object: One with the JDO annotations for persisting it on the server and another which is serialisable and used over RPC?
I notice the Stock Watcher has separate classes and I can theorise why:
Otherwise the gwt compiler would try
to generate javascript for everything
the persisted class referenced like
JDO and com.google.blah.users.User, etc
Also there may be logic on the server-side
class which doesn't apply to the client
and vice-versa.
I just want to make sure I'm understanding this correctly. I don't want to have to create two versions of all my business object classes which I want to use over RPC if I don't have to.
The short answer is: you don't need to create duplicate classes.
I recommend that you take a look from the following google groups discussion on the gwt-contributors list:
http://groups.google.com/group/google-web-toolkit-contributors/browse_thread/thread/3c768d8d33bfb1dc/5a38aa812c0ac52b
Here is an interesting excerpt:
If this is all you're interested in, I
described a way to make GAE and
GWT-RPC work together "out of the
box". Just declare your entities as:
#PersistenceCapable(identityType =
IdentityType.APPLICATION, detachable
= "false") public class MyPojo implements Serializable { }
and everything will work, but you'll
have to manually deal with
re-attachment when sending objects
from the client back to the server.
You can use this option, and you will not need a mirror (DTO) class.
You can also try gilead (former hibernate4gwt), which takes care of some details within the problems of serializing enhanced objects.
Your assessment is correct. JDO replaces instances of Collections with their own implementations, in order to sniff when the object graph changes, I suppose. These implementations are not known by the GWT compiler, so it will not be able to serialize them. This happens often for classes that are composed of otherwise GWT compliant types, but with JDO annotations, especially if some of the object properties are Collections.
For a detailed explanation and a workaround, check out this pretty influential essay on the topic: http://timepedia.blogspot.com/2009/04/google-appengine-and-gwt-now-marriage.html
I finally found a solution. Don't change your object at all, but for the listing do it this way:
List<YourCustomObject> secureList=(List<YourCustomObject>)pm.newQuery(query).execute();
return new ArrayList<YourCustomObject>(secureList);
The actual problem is not in Serializing the Object... the problem is to Serialize the Collection class which is implemented by Google and is not allowed to Serialize out.
You do not have to create two versions of the domain model.
Here are two tips:
Use a String encoded key, not the Appengine Key class.
pojo = pm.detachCopy(pojo)
...will remove all the JDO enhancements.
You don't have to create separate instances at all, in fact you're better off not doing it. Your JDO objects should be plain POJOs anyway, and should never contain business logic. That's for your business layer, not your persistent objects themselves.
All you need to do is include the source for the annotations you are using and GWT should compile your class just fine. Also, you want to avoid using libraries that GWT can't compile (like things that use reflection, etc.), but in all the projects I've done this has never been a problem.
I think that a better format to send objects through GWT is through JSON. In this case from the server a JSON string would be sent which would then have to be parsed in the client. The advantage is that the final Javascript which is rendered in the browser has a smaller size. thus causing the page to load faster.
Secondly to send objects through GWT, the objects should be serializable. This may not be the case for all objects
Thirdly GWT has inbuilt functions to handle JSON... so no issues on the client end