I'm developing a GWT project at the moment and it's been up and running for a while. New functionality that is to be added require extensive testing, visualizing and simulating of a specific algorithm. I would like to export that specific algorithm so that I may call it directly from JavaScript and do some canvas magic.
How can I export a number of classes for direct use in JavaScript from a GWT project?
I've tried using the GWT exporter, following the Getting Started section closely.
I've noticed that my output directory contains a new generator class (TestClassExporterImpl.java) but the final JavaScript output contains no trace of my TestClass or the exported methods.
I'm sure I've made a mistake somewhere on the way or didn't understand the GWT exporter correctly.
Try to disable obfuscation, it will create the same names in Javascript as in the original Java code
Related
I try to create the entity like this:
DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
Entity stock = new Entity("Stock", 1);
stock.setProperty("Stock", "FCB");
ds.put(stock);
but keep getting the error:
No source code is available for type com.google.appengine.api.datastore.DatastoreService; did you forget to inherit a required module?
The error means just what it says, the GWT compiler needs access to the Java source it compiles to Javascript, and obviously DatastoreService is not something that should exist on the frontend - so you have an architecture issue here.
You'll need to write a proxy that can call a server component (Which in turns calls the DatastoreService) and returns DTOs/value objects (that you define and thus have the source for).
Cheers,
No source code is available
GWT transliterate Java to Javascript, reading it's source code and there a limited language support.
What you're trying to achieve is a Server only operation and you're adding this operation within the client code, which will run on a browser. Neither GAE allow this or GWT has the source of these classes nor capability to do so.
Solution
You need to create a request to your server that will access the DatastoreService , the return the output to the client code.
Below a example of a properly architect GWT web application:
In GWT web/production mode, Java code is complied into Javascript code that is rendered in the browser.
Also,I have always thought that in GWT development mode, GWT developer plugin compiles my Java code into JavaScript to render it in the browser. But after reading on some site, I came to know that there's no compiling of code to JavaScript to view it in the browser in development mode.
So, I wonder: What are all these widgets I see in the browser during this mode if they aren't JavaScript code?. I don't understand it.
Please help understanding this.
The crux of the Dev Mode is that your code runs in Java. This is a prerequisite if you can use a standard Java debugger. You'll find a high-level overview in the GWT documentation.
The magic happens with JSNI methods and overlay types: when a class is loaded, all its JSNI methods are extracted and their JS body is sent to the browser, ready to be executed (as JavaScript then), and the class is rewritten on the fly to reimplement the JSNI method to make a call to the browser (via the Dev Plugin you installed there and is triggered by ?gwt.codesvr= in the URL) to execute the corresponding JS function. This is the reason why Java objects are seen as opaque handles in JSNI methods; they're assigned a numeric ID to pair the Java object with a dummy JS object on the server-side. A similar though more complex rewriting is done for overlay types, and the same ID mapping is used when JS objects are passed to Java code (as overlay types).
BTW, Super Dev Mode compiles to JavaScript (almost) on the fly.
I have a Qt application containing a Webkit module and using Dart (compiled to JS). It's like a bare-bones browser written in Qt. The application basically replaces certain text on the webpage with different text. I want users to be able to make their own Dart files to replace their own text with their own different text.
Any recommendations for approaches to creating a plugin system?
I think that this question needs a little clarification: are you asking about using Dart for scripting Qt applications (where Dart plays the role of a scripting language), or are you asking about a plugin system for Dart application that is compiled to JS and used in a Qt application, probably via QtScript (in which case, the role of a scripting language is played by JavaScript)?
I presume that it is the latter variant (and I don't know enough about Qt to be able to answer about the former variant anyway).
Let's assume that all plugins for the Dart application are available at the build time of that Qt application, so that you don't need to compile Dart to JS dynamically. Then, if you compile a Dart script, resulting JS will include all necessary code from its #imports. All you need is to create a proper script that imports all plugins and calls them (importing isn't enough, as dead code will be eliminated).
Maybe an example will be more instructive. Let's say that you want to allow plugins to do some work on a web page. One way you might structure it is that every plugin will be a separate #library with a top-level function of a well known name (say doWork). Example of a plugin:
// my_awesome_plugin.dart
#library('My Awesome Plugin')
doWork(page) {
page.replaceAll('JavaScript is great', 'Dart is great');
}
You can have as many plugins of this nature as you wish. Then, you would (at the build time) generate a following simple main script in Dart:
// main.dart
// these lines are automatically generated -- for each plugin file,
// one #import with unique prefix
#import('my_awesome_plugin.dart', prefix: 'plugin1');
#import('another_plugin.dart', prefix: 'plugin2');
main() {
var page = ...; // provided externally, from your Qt app
// and these lines are automatically generated too -- for each plugin,
// call the doWork function (via the prefix)
plugin1.doWork(page);
plugin2.doWork(page);
}
Then, if you compile main.dart to JavaScript, it will include all those plugins.
There are other possibilities to structure the plugin system: each plugin could be a class implementing a specific interface (or inheriting from a specific base class), but the general approach would be the same. At least the approach that I would recommend -- making each plugin a separate library.
You probably don't like the step with generating the main script automatically, and I don't like it either. But currently, Dart only allows one way to dynamically load new code: spawning new isolates. I'm not sure how (or even if) that would work in QtScript, because isolates are implemented as web workers when compiled to JavaScript, so I won't discuss this here.
Things will get more complicated if you want to support compiling Dart scripts at the runtime of your Qt application, but I think that I'm already guessing too much about your project and I might be writing about something you don't really need. So I'll finish it like this for now.
I am a newbie at GWT and I have the following query.
I have a scenario where I am trying to develop a web interface(using GWT) for an existing application.
In the client side class file I would like to invoke a user specific class file, i understand that this is due to the fact that i am trying to invoke classes other than the ones http://code.google.com/webtoolkit/doc/latest/RefJreEmulation.html
I would like to know how this code can be called from the client side of the ui.
Thanks and Regards,
Bhavya
If you have a source code for the class you want to use and it is using only the supported Java classes, you can simply add your specific classes to client packages. If this is a reusable code, you can create a new GWT module and inherit it in your application. You can also simply move those classes to your client packages OR add a new client folder in you .gwt.xml file (add one more <source> tag)
If your class is not compilable by GWT, then I think you need to use it through RPC service.
If the code is translatable into JavaScript, you could for example put your individual class files into a jar and add it to the Build Path - as you would do in a 'regular' Java Project.
I have seen that GWT framework is having generator feature.
In what case we have to use gwt generator option and why it is needed?
Can anyone tell me simply why,what is gwt generator? Done some googling. But not much helpful stuffs...
From this tutorial:
Generators allow the GWT coder to generate Java code at compile time and have it then be compiled along with the rest of the project into JavaScript.
This tutorial uses the example of generating a Map of values at compile time based on a properties file.
I've done GWT development for 3 years now and I've written one generator :) I've written a couple of linkers for experimental purposes so I think they are more common, though still rare. The classic case is where you want to write
X x = GWT.create(X.class)
and have the particular subclass or implementation of X constructed at compile time based on, perhaps, annotations in the provided X class or interface. GWT uses them for things like the CSSResource.
Search for "GWT Generator Experiments" site:development.lombardi.com on google for some info about what I did.
One of the use cases is to mimic reflection on the client side by building a factory class on the fly. I remember answering a question posted by you earlier on how to do this
How to create new instance from class name in gwt?
So i guess you already know the application. What else are you looking for? Can you be precise?
I've started using GWT Generators where I needed Java Reflection. I've documented One of the use cases for using GWT generators here:
http://jpereira.eu/2011/01/30/wheres-my-java-reflection/
Hope it helps.
If you refer to code generator, yes, there will a tool supporting GWT 2.1 code generation. For more details and a quick start, see http://www.springsource.org/roo/start
A general roo intro is here http://blog.springsource.com/2009/05/01/roo-part-1/
Another visual tutorial is at http://www.thescreencast.com/2010/05/how-to-gwt-roo.html
Check out this implementation:
http://samuelschmid.blogspot.com/2012/05/using-generator-for-generic-class.html
You can create new Instances of classes on client with foo.newInstance("fully.qualified.class.name");