I am using the resty-gwt library and wondering if it would be possible to use the JsonEncoderDecoder interface dynamically?
eg. I have a pojo as follows:
#JsonTypeInfo(use=Id.CLASS, include=As.PROPERTY, property="class")
public class MyObject {....}
With the class name returned in the response: is it possible using generators to generate the interface
public interface MyObjectCodec extends JsonEncoderDecoder<MyObject > {}
and somehow make a call to GWT.create(MyObjectCodec.class)
so that I can decode the object?
I believe you can even if I have never tried.
Extract from restyGWT.gwt.xml
<generate-with class="org.fusesource.restygwt.rebind.RestServiceGenerator">
<when-type-assignable class="org.fusesource.restygwt.client.RestService" />
</generate-with>
<generate-with class="org.fusesource.restygwt.rebind.JsonEncoderDecoderGenerator">
<when-type-assignable class="org.fusesource.restygwt.client.JsonEncoderDecoder" />
</generate-with>
<generate-with class="org.fusesource.restygwt.rebind.DirectRestServiceGenerator">
<when-type-assignable class="org.fusesource.restygwt.client.DirectRestService" />
</generate-with>
So if you are writing a JsonEncoderDecoder the generator should generate the code for you.
You should be able to use the method JSONValue encode(T value) to encode your object in JSONValue
I do not know what you mean by dynamic but IMO it is all "static" meaning it does not really depends on runtime variables or anything.
Related
I am very new to GWT.
I am using ext-gwt widgets.
I found many places in my office code containing like,
class A extends BaseModel{
private UserAccountDetailsDto userAccountDetailsDto = null;
//SETTER & GETTER IN BASEMODEL WAY
}
Also, the DTO reference is unused.
public class UserAccountDetailsDto implements Serializable{
private Long userId=null;
private String userName=null;
private String userAccount=null;
private String userPermissions=null;
//NORMAL SETTER & GETTER
}
Now, I am able to get the result from GWT Server side Code and things Work fine, but when I comment the DTO reference inside the class A, I am not getting any Result.
Please explain me the need of that.
Thanks
Well the problem is in implementation of GXT BaseModel and GWT-RPC serialization.
BaseModel is based around special GXT map, RpcMap. This map has defined special serialization rules, which let's avoid RPC type explosion, but as side effect, only some simple types stored in map will be serialized. E.g. you can put any type inside the map, but if you serialize/deserialize it, only values of type Integer, String ,Double,Byte, Float and Short (and arrays of this types) will be present. So the meaning behind putting reference to the DTO inside BaseModel, is to tell GWT-RPC that this type is also have to be serialized.
Detailed explanation
Basically GWT-RPC works like this:
When you define an interface for service, GWT-RPC analyzes all the classes used in parameters/ return type, to create serializers/deserializers. If you return something like Map<Object,Object> from your service, GWT-RPC will have to create a serializer for each class which implements Map and Serializable interfaces, but also it will generate serializers for each class which implements Serializable. In the end it is quite a bad situation, because the size of your compiled js file will be much biggger. This situation is called GWT-RPC type explosion.
So, in the BaseModel, all values are stored in RpcMap. And RpcMap has custom written serializer (RpcMap_CustomFieldSerializer you can see it's code if you interested how to create such things), so it doesn't cause the problem described above. But since it has custom serializer GWT dosn't know which custom class have been put inside RpcMap, and it doesn't generate serializers for them. So when you put some field into your BaseModel class, gwt knows that it might need to be able to serialize this class, so it will generate all the required stuff for this class.
Porting GXT2 Application code using BaseModel to GXT3 Model is uphill task. It would be more or less completely rewrite on model side with ModelProviders from GXT3 providing some flexibility. Any code that relies on Model's events, store, record etc are in for a rewrite.
this is a situation I would like to implement.
public class ComponentRepository
{
public void Register(IComponent component)
{
// store component in collection
}
}
<!-- root context -->
<object id="Repository" type="NameSpace.ComponentRepository" />
<!-- child context (0 - n contexts) -->
<object id="Component" type="NameSpace.Component"/>
I would like to register all IComponent objects with ComponentRepository. I suppose it can be done with some kind of publish/subscribe mechanism, but I would like to keep my classes clean (without implementing any of spring.net interfaces).
What is the best way to achieve this?
I understood your question as this:
After the instantiation of the child-context's Component, the Register-method of a ComponentRepository defined in another context should be called.
As far as I know, there is no xml-declarative way to achieve what you want.
I would suggest to either make your ComponentRepository IApplicationContextAware (which is what you explicitly don't want) or to create a new IApplicationContextAware Class which takes a dependency of ComponentRepository.
That way you can call the ApplicationContext's GetObjectsOfType Method and retrieve all IComponent objects to pass to the ComponentRepository.
Can I use enum values as field values inside UiBinder template ? I'm using GWT 2.4
Something like this
<ui:with field="en" type="com.mine.courierApp.shared.PayerType" />
looks promising, where
public enum PayerType
{
Sender,
Recipient
}
but I can't refer to values of the enum by en.Sender.
Is it even possible ?
<ui:import field='com.mine.courierApp.shared.PayerType.Sender' />
or
<ui:import field='com.mine.courierApp.shared.PayerType.*' />
And then you can use it as payerType='{Sender}'.
But UiBinder should automatically try to translate enum constant names into values, so the following should work without any need for a ui:with:
<my:MyWidget payerType='Sender' />
If the MyWidget widget has a public void setPayerType(PayerType type) method, UiBinder should look for an enum value named Sender (from the *.ui.xml file) in the PayerType enum (from the method's argument type).
If you don't ui:import the enum class like this:
<ui:import field='com.mine.courierApp.shared.PayerType.*' />
then you don't get content-assist, which the whole point of this in the first place.
But then you run into another issue...
Although you can simple type { ctrl-space } to get a popup menu of the enum value, if you are using, say, bootstrap3, there are various enums that each have their own "DEFAULT" value. The ui template editor will complain about that; i.e. if you start making extensive use of this content-assist feature, you will need to ensure the imported enums have unique value names.
For example, I've got a simple schema which imports another schema. The second schema (urn:just:attributes, just-attributes.xsd) just defines an attribute group.
<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.example.org/MySchema"
xmlns:tns="http://www.example.org/MySchema"
elementFormDefault="qualified"
xmlns:ja="urn:just:attributes">
<import schemaLocation="just-attributes.xsd" namespace="urn:just:attributes"/>
<element name="MyElement">
<complexType>
<attributeGroup ref="ja:AttributeGroup"/>
</complexType>
</element>
</schema>
I'm using the Metro xjc Ant task to generate classes off of this schema. The problem I'm running into is that the third party application I'm interacting with is peculiar about namespaces. This case I need a String value, so I have to serialize it. I use boilerplate code for this.
private static <T> String marshal(T object) throws JAXBException{
OutputStream outputStream = new ByteArrayOutputStream();
JAXBContext jaxbContext = JAXBContext.newInstance(object.getClass());
Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.marshal(object, outputStream);
return outputStream.toString();
}
Which gives me something along the lines of
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:MyElement xmlns:ns1="urn:just:attributes" xmlns:ns2="http://www.example.org/MySchema" ns1:attrib1="1234" ns1:attrib2="5678"/>
The problem I have is that this third party expects something like xmlns:thirdpartyns="urn:just:attributes", which is to say, they are parsing based on the name given to the namespace. It has to be "thirdpartyns" for their software to work.
Does anyone know of a way around this, short of doing a find and replace in the resulting string? A custom binding rule perhaps?
http://hwellmann.blogspot.com/2011/03/jaxb-marshalling-with-custom-namespace.html
This shows how to do it.
Another:
http://www.systemmobile.com/?p=280
Key bits in case that link dies too:
the NamespacePrefixMapper class, found in the com.sun.xml.bind.marshaller package. The abstract class has one method to implement:
public abstract String getPreferredPrefix(
String namespaceUri,
String suggestion,
boolean requirePrefix);
then
Marshaller marshaller =
jaxbContext.createMarshaller();
marshaller.setProperty(”com.sun.xml.bind.namespacePrefixMapper”,
new MyNamespacePrefixMapper());
If you’re also using javax.xml.xpath.XPath, your NamespacePrefixMapper can also implement javax.xml.namespace.NamespaceContext, centralizing your namespace customization in a single class.
I tested that in Java SE6 and it requires a small change compared to the solution for Java SE 5 (as described above):
Marshaller m = context.createMarshaller();
m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE );
m.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
m.setProperty("com.sun.xml.internal.bind.namespacePrefixMapper", mapper);
So the third property from above contains the additional .internal. in the package name compared to the Java SE5 version.
What I did not find out yet is how to tell the Marshaller which namespace URI becomes the default namespace (""). If I override the method getPreferredPrefix() and return an empty string, the Marshaller has issues with writing attributes of the default namespace (in this case it creates a new namespace called ns1)
I had the same question. In package-info.java (if you don't have it, you can just manually create it) add the xmlns part:
#javax.xml.bind.annotation.XmlSchema(xmlns = {
#javax.xml.bind.annotation.XmlNs(namespaceURI = "urn:just:attributes", prefix = "thirdpartyns") },
elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED)
There is a way of doing this, which uses an internal JAXB implementation class called NamespacePrefixMapper. In the JAXB RI, this is in com.sun.xml.bind.marshaller, but in Java6, it's in com.sun.xml.internal.bind.marshaller.
This is an abstract class, which you can subclass and implement the abstract method which maps namespace URIs on to prefixes.
You then inject an instance of that subclass into the marshaller:
JAXBContext context = ...
Marshaller marshaller = context.createMarshaller();
NamespacePrefixMapper prefixMapper = new MyPrefixMapperImpl();
marshaller.setProperty("com.sun.xml.bind.namespacePrefixMapper", prefixMapper);
The property name is going to be different for the Java6 version, but you get the idea.
Note that this is an internal JAXB implementation class, so there's no guarantee it'll be there in future versions.
GWT.create() is the reflection equivalent in GWT,
But it take only class literals, not fully qualified String for the Class name.
How do i dynamically create classes with Strings using GWT.create()?
Its not possible according to many GWT forum posts but how is it being done in frameworks like Rocket-GWT (http://code.google.com/p/rocket-gwt/wiki/Ioc) and Gwittir (http://code.google.com/p/gwittir/wiki/Introspection)
It is possible, albeit tricky. Here are the gory details:
If you only think as GWT as a straight Java to JS, it would not work. However, if you consider Generators - Special classes with your GWT compiler Compiles and Executes during compilation, it is possible. Thus, you can generate java source while even compiling.
I had this need today - Our system deals with Dynamic resources off a Service, ending into a String and a need for a class. Here is the solutuion I've came up with - btw, it works under hosted, IE and Firefox.
Create a GWT Module declaring:
A source path
A Generator (which should be kept OUTSIDE the package of the GWT Module source path)
An interface replacement (it will inject the Generated class instead of the interface)
Inside that package, create a Marker interface (i call that Constructable). The Generator will lookup for that Marker
Create a base abstract class to hold that factory. I do this in order to ease on the generated source code
Declare that module inheriting on your Application.gwt.xml
Some notes:
Key to understanding is around the concept of generators;
In order to ease, the Abstract base class came in handy.
Also, understand that there is name mandling into the generated .js source and even the generated Java source
Remember the Generator outputs java files
GWT.create needs some reference to the .class file. Your generator output might do that, as long as it is referenced somehow from your application (check Application.gwt.xml inherits your module, which also replaces an interface with the generator your Application.gwt.xml declares)
Wrap the GWT.create call inside a factory method/singleton, and also under GWT.isClient()
It is a very good idea to also wrap your code-class-loading-calls around a GWT.runAsync, as it might need to trigger a module load. This is VERY important.
I hope to post the source code soon. Cross your fingers. :)
Brian,
The problem is GWT.create doen't know how to pick up the right implementation for your abstract class
I had the similar problem with the new GWT MVP coding style
( see GWT MVP documentation )
When I called:
ClientFactory clientFactory = GWT.create(ClientFactory.class);
I was getting the same error:
Deferred binding result type 'com.test.mywebapp.client.ClientFactory' should not be abstract
All I had to do was to go add the following lines to my MyWebapp.gwt.xml file:
<!-- Use ClientFactoryImpl by default -->
<replace-with class="com.test.mywebapp.client.ClientFactoryImpl">
<when-type-is class="com.test.mywebapp.client.ClientFactory"/>
</replace-with>
Then it works like a charm
I ran into this today and figured out a solution. The questioner is essentially wanting to write a method such as:
public <T extends MyInterface> T create(Class<T> clz) {
return (T)GWT.create(clz);
}
Here MyInterface is simply a marker interface to define the range of classes I want to be able to dynamically generate. If you try to code the above, you will get an error. The trick is to define an "instantiator" such as:
public interface Instantiator {
public <T extends MyInterface> T create(Class<T> clz);
}
Now define a GWT deferred binding generator that returns an instance of the above. In the generator, query the TypeOracle to get all types of MyInterface and generate implementations for them just as you would for any other type:
e.g:
public class InstantiatorGenerator extends Generator {
public String generate(...) {
TypeOracle typeOracle = context.getTypeOracle();
JClassType myTYpe= typeOracle.findType(MyInterface.class.getName());
JClassType[] types = typeOracle.getTypes();
List<JClassType> myInterfaceTypes = Collections.createArrayList();
// Collect all my interface types.
for (JClassType type : types) {
if (type.isInterface() != null && type.isAssignableTo(myType)
&& type.equals(myType) == false) {
myInterfaceTypes.add(type);
}
for (JClassType nestedType : type.getNestedTypes()) {
if (nestedType.isInterface() != null && nestedType.isAssignableTo(myType)
&& nestedType.equals(myTYpe) == false) {
myInterfaceTypes.add(nestedType);
}
}
}
for (JClassType jClassType : myInterfaceTypes) {
MyInterfaceGenerator generator = new MyInterfaceGenerator();
generator.generate(logger, context, jClassType.getQualifiedSourceName());
}
}
// Other instantiator generation code for if () else if () .. constructs as
// explained below.
}
The MyIntefaceGenerator class is just like any other deferred binding generator. Except you call it directly within the above generator instead of via GWT.create. Once the generation of all known sub-types of MyInterface is done (when generating sub-types of MyInterface in the generator, make sure to make the classname have a unique pattern, such as MyInterface.class.getName() + "_MySpecialImpl"), simply create the Instantiator by again iterating through all known subtypes of MyInterface and creating a bunch of
if (clz.getName().equals(MySpecialDerivativeOfMyInterface)) { return (T) new MySpecialDerivativeOfMyInterface_MySpecialImpl();}
style of code. Lastly throw an exception so you can return a value in all cases.
Now where you'd call GWT.create(clz); instead do the following:
private static final Instantiator instantiator = GWT.create(Instantiator.class);
...
return instantiator.create(clz);
Also note that in your GWT module xml, you'll only define a generator for Instantiator, not for MyInterface generators:
<generate-with class="package.rebind.InstantiatorGenerator">
<when-type-assignable class="package.impl.Instantiator" />
</generate-with>
Bingo!
What exactly is the question - i am guessing you wish to pass parameters in addition to the class literal to a generator.
As you probably already know the class literal passed to GWT.create() is mostly a selector so that GWT can pick and execute a generator which in the end spits out a class. The easist way to pass a parameter to the generator is to use annotations in an interface and pass the interface.class to GWT.create(). Note of course the interface/class must extend the class literal passed into GWT.create().
class Selector{
}
#Annotation("string parameter...")
class WithParameter extends Selector{}
Selector instance = GWT.create( WithParameter.class )
Everything is possible..although may be difficult or even useless. As Jan has mentioned you should use a generator to do that. Basically you can create your interface the generator code which takes that interface and compile at creation time and gives you back the instance. An example could be:
//A marker interface
public interface Instantiable {
}
//What you will put in GWT.create
public interface ReflectionService {
public Instantiable newInstance(String className);
}
//gwt.xml, basically when GWT.create finds reflectionservice, use reflection generator
<generate-with class="...ReflectionGenerator" >
<when-type-assignable class="...ReflectionService" />
</generate-with>
//In not a client package
public class ReflectionGenerator extends Generator{
...
}
//A class you may instantiate
public class foo implements Instantiable{
}
//And in this way
ReflectionService service = GWT.create(ReflectionService.class);
service.newInstance("foo");
All you need to know is how to do the generator. I may tell you that at the end what you do in the generator is to create Java code in this fashion:
if ("clase1".equals(className)) return new clase1();
else if ("clase2".equals(className)) return new clase2();
...
At the final I thought, common I can do that by hand in a kind of InstanceFactory...
Best Regards
I was able to do what I think you're trying to do which is load a class and bind it to an event dynamically; I used a Generator to dynamically link the class to the event. I don't recommend it but here's an example if it helps:
http://francisshanahan.com/index.php/2010/a-simple-gwt-generator-example/
Not having looked through the code of rocket/gwittir (which you ought to do if you want to find out how they did it, it is opensource after all), i can only guess that they employ deferred binding in such a way that during compile time, they work out all calls to reflection, and statically generate all the code required to implement those call. So during run-time, you cant do different ones.
What you're trying to do is not possible in GWT.
While GWT does a good job of emulating Java at compile time the runtime is of course completely different. Most reflection is unsupported and it is not possible to generate or dynamically load classes at runtime.
I had a brief look into code for Gwittir and I think they are doing their "reflection stuff" at compile time. Here: http://code.google.com/p/gwittir/source/browse/trunk/gwittir-core/src/main/java/com/totsp/gwittir/rebind/beans/IntrospectorGenerator.java
You might be able to avoid the whole issue by doing it on the server side. Say with a service
witch takes String and returns some sort of a serializable super type.
On the server side you can do
return (MySerializableType)Class.forName("className").newInstance();
Depending on your circumstances it might not be a big performance bottleneck.