Scenario: I have a GWT web application running within a JavaFX WebView/WebEngine. I am able to pass Strings from GWT to JavaScript to JavaFX without any issues.
Problem: When passing an array of custom objects like Data[] in the same fashion, the result on the JavaFX side is null.
An example of what Data looks like:
public class Data extends Serializable
{
char[] name;
int code;
short bar;
}
Here's the code to send the data to JavaScript:
public static native void doNativeStuff(String id, Data[] data) /*-{
$wnd.javaInterface.doStuff(id, data);
}-*/;
I've verified in the debugger that the Java object being passed in is populated with data and looks good.
Now on the JavaFX side, I have the following code to add the javaInterface to the page:
JSObject win = (JSObject) engine.executeScript("window");
win.setMember("javaInterface", new JavaInterface());
I know that this works because I'm using it for other methods that pass only Strings and they work great.
public void doStuff(String id, Data[] data)
{
// Right here, id == "validId" and data == null
if (data != null)
{
... do what is needed ...
}
}
Note that the Data object is defined and accessible on both sides.
From the GWT documentation:
Incoming Java type How it appears to JavaScript code
Java array opaque value that can only be passed back into Java code
I'm not touching it in JavaScript at all and I'm only passing it through from Java->JavaScript->Java, but the final step appears to be what is failing.
I've spent the last few hours scouring Stack Overflow, Google, GWT groups, gwtproject.org, etc. But most all of the examples only show a single argument being passed through and almost none of them show a Java Array being used.
I'd much rather just pass the object through rather than going to->from JSON, but I did give that a try out of desperation. I tried to use GSON but it doesn't work on the GWT client side. I tried to use the GWT AutoBean Framework but my Data object isn't a valid bean (I think because of no default constructor) and I cannot change that at this time.
I'm not using any Long or long values.
I've seen examples like this:
#com.google.gwt.examples.JSNIExample::staticFoo(Ljava/lang/String;)(s);
But from what I can tell that's just for going from JavaScript to GWT over JSNI. I'm trying to go the other way. I also couldn't find an example of this for multiple arguments.
I'm sure that there is just a minor tweak here that I'm missing, but I haven't been able to figure it out just yet. Please let me know if you see something that I'm missing here.
opaque value that can only be passed back into Java code
I think this means you cannot pass Java array into JavaScript code.
Agree with jat. I used to provide support for the similar needs and I had to serialize the objects myself.
And you can pass multiple arguments like this (types of arguments are given just for example):
private native void doJSAction(MyClass handler)/*-{
// do smth in JS
// then call external non-static method
handler.#com.myclient.helper.MyClass::doMyAction(Lcom/google/gwt/core/client/JavaScriptObject;Ljava/lang/String;Lcom/myclient/helper/MyClass;II)(jsNativeSmth, myString, handler, intA, intB);
}-*/;
where doMyAction is something like the following:
void doMyAction(JavaScriptObject jsObject, String s, MyClass instance, int a, int b)
I haven't played with JavaFX, but since it runs in a different VM and knows nothing about the GWT DevMode protocol (for example, a Java object is wrapped in a JS object that basically makes RPC calls to manipulate it), I am pretty sure you are going to have to serialize everything between GWT and JavaFX as Strings and primitives.
Related
I have the following entity in GWT
#JsType(namespace = "my.entities")
public class MyEntity {
private Set<String> texts;
public Set<String> getTexts(){
if(this.texts==null)
this.texts=new LinkedHashSet<String>();
return this.texts;
}
public void setTexts(Set<String> texts){
this.texts=texts;
}
}
When I call myEntityVar.getTexts() in Javascript the returned object is a HashSet. It seems like jsinterop converts the java implementation of HashSet to JavaScript. But how can I create a new HashSet in JavaScript in order to use myEntityVar.setTexts(texts)? I tried an array for the "texts" param, but that doesn't work. So I somehow need to use HashSet in JavaScript.
However, I can't figure out, where to find it.
Any idea?
The short answer is that you can't - but then again, you also can't create a plain HashSet in JS either!
The reason that this works at all is that you've enabled -generateJsInteropExports, and while there is a JsInterop annotation on your MyEntity type, there is also one on java.util.Set (and a few other base JRE types). This allows for your code to return emulated java Sets without issue - any method which is compatible with running in JS is supported.
There are a few downsides:
Compiled size increases somewhat, since even if you don't use a method, it must be compiled in to your app this way, just in case JS uses it
Some methods are not supported - JS doesn't really have method overloading, so toArray() and toArray(T[]) look like the same method in JS. GWT solves this by not supporting the second method at all. (java.util.List has the same issue with remove(T) and remove(int), but it resolves it by renaming remove(int) to removeAtIndex(int) when compiled.)
If you never return these types, you'll probably want to disable this feature entirely - the -excludeJsInteropExports and -includeJsInteropExports flags to the compiler let you control what is exported.
To answer your question more directly, you have a few options that I can see:
Allow the setTexts method to be passed something else from JS, such as a JsArrayLike so that you could let users pass in a plain JS array of strings, or even a JS Set. You could go further and accept Object, and then type-check it to see what was passed in. You could even leave the Set override so it could be called from your own Java if necessary, but mark it as #JsIgnore so that GWT doesn't break when you attempt to export overloaded methods.
Create a factory method somewhere to create the Set implementation you would like your JS users to use. Since add and remove are supported, the calling JS code can build up the set before passing it in. Something like this:
#JsMethod(namespace = "my.Util")
public static <T> LinkedHashSet<T> createSet() {
return new LinkedHashSet<>();
}
Now they can call my.Util.createSet(), append items, and then pass it to your setTexts method.
Finally having gotten GWT-Jackson-APT processors working and properly generating code for my classes, the one remaining hiccup I have is that for some reason gwt-jackson-apt uses the window JSON stringify (& parse) function.
$wnd.window.JSON.stringify(STRING)
The problem is that due to this being on a web-worker, $wnd.window is not defined. Even though JSON.stringify() is available in web-worker, the result is that the code won't run correctly, even though if I modify it to be just JSON.stringify() before uploading it works pefectly.
Is there a clean way to redefine which of these functions gets used in this instance?
What is the best means of going about fixing this so that my web-worker code doesn't try to call the functions that are not available in their context.
The library right now uses the elemental2 version of JSON Global.JSON.stringify
and if we look at the implementation of the JSON in the Global class we will find that it is assigned to the window instance here :
#JsType(isNative = true, name = "window", namespace = JsPackage.GLOBAL)
public class Global {
public static JSONType JSON;
}
when this is used as Global.JSON.stringify(someJsonObject) from GWT java code when compile it will produce $wnd.window.JSON.stringify(someJsonObject) or something very similar.
in order to fix this we need to access the native JSON in a different way that does not link it the current window instance.
one solution to this is to use JsInterop to interface directly with the JSON, something like this
#JsType(isNative = true, namespace = JsPackage.GLOBAL)
public class JSON {
public native static String stringify(Object jsonObj);
}
with this implementation we can use the JSON without the window prefix and when we use it in java like this JSON.stringify(someJsonObject) and notice how we no longer use the one from Global we end up with a generated Js that looks like this $wnd.JSON.stringify(someJsonObject)
i run a small test and implemented this JSON in the jackson-apt lib and switched to use the new implementation instead of using Global.JSON and all tests passed.
to me this looks like a good issue to be reported on the project repository. and i will apply the fix ASAP.
I am attempting to call out to parallels.js via JSNI. Parallels provides a nice API around web workers, and I wrote some lightweight wrapper code which provides a more convenient interface to workers from GWT than Elemental. However I'm getting an error which has me stumped:
com.google.gwt.core.client.JavaScriptException: (DataCloneError) #io.mywrapper.workers.Parallel::runParallel([Ljava/lang/String;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)([Java object: [Ljava.lang.String;#1922352522, JavaScript object(3006), JavaScript object(3008)]): An object could not be cloned.
This comes from, in hosted mode:
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:249) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:299) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107) at io.mywrapper.workers.Parallel.runParallel(Parallel.java)
Here's my code:
Example client call to create a worker:
Workers.spawnWorker(new String[]{"hello"}, new Worker() {
#Override
public String[] work(String[] data) {
return data;
}
#Override
public void done(String[] data) {
int i = data.length;
}
});
The API that provides a general interface:
public class Workers {
public static void spawnWorker(String[] data, Worker worker) {
Parallel.runParallel(data, workFunction(worker), callbackFunction(worker));
}
/**
* Create a reference to the work function.
*/
public static native JavaScriptObject workFunction(Worker worker) /*-{
return worker == null ? null : $entry(function(x) {
worker.#io.mywrapper.workers.Worker::work([Ljava/lang/String;)(x);
});
}-*/;
/**
* Create a reference to the done function.
*/
public static native JavaScriptObject callbackFunction(Worker worker) /*-{
return worker == null ? null : $entry(function(x) {
worker.#io.mywrapper.workers.Worker::done([Ljava/lang/String;)(x);
});
}-*/;
}
Worker:
public interface Worker extends Serializable {
/**
* Called to perform the work.
* #param data
* #return
*/
public String[] work(String[] data);
/**
* Called with the result of the work.
* #param data
*/
public void done(String[] data);
}
And finally the Parallels wrapper:
public class Parallel {
/**
* #param data Data to be passed to the function
* #param work Function to perform the work, given the data
* #param callback Function to be called with result
* #return
*/
public static native void runParallel(String[] data, JavaScriptObject work, JavaScriptObject callback) /*-{
var p = new $wnd.Parallel(data);
p.spawn(work).then(callback);
}-*/;
}
What's causing this?
The JSNI docs say, regarding arrays:
opaque value that can only be passed back into Java code
This is quite terse, but ultimately my arrays are passed back into Java code, so I assume these are OK.
EDIT - ok, bad assumption. The arrays, despite only ostensibly being passed back to Java code, are causing the error (which is strange, because there's very little googleability on DataCloneError.) Changing them to String works; however, String isn't sufficient for my needs here. Looks like objects face the same kinds of issues as arrays do; I saw Thomas' reference to JSArrayUtils in another StackOverflow thread, but I can't figure out how to call it with an array of strings (it wants an array of JavaScriptObjects as input for non-primitive types, which does me no good.) Is there a neat way out of this?
EDIT 2 - Changed to use JSArrayString wherever I was using String[]. New issue; no stacktrace this time, but in the console I get the error: Uncaught ReferenceError: __gwt_makeJavaInvoke is not defined. When I click on the url to the generated script in developer tools, I get this snippet:
self.onmessage = function(e) {self.postMessage((function (){
try {
return __gwt_makeJavaInvoke(3)(null, 65626, jsFunction, this, arguments);
}
catch (e) {
throw e;
}
})(e.data))}
I see that _gwt_makeJavaInvoke is part of the JSNI class; so why would it not be found?
You can find working example of GWT and WebWorkers here: https://github.com/tomekziel/gwtwwlinker/
This is a preliminary work, but using this pattern I was able to pass GWT objects to and from webworker using serialization provided by AutoBeanFactory.
If you never use dev mode it is currently safe to pretend that a Java String[] is a JS array with strings in it. This will break in dev mode since arrays have to be usable in Java and Strings are treated specially, and may break in the future if the compiler optimizes arrays differently.
Cases where this could go wrong in the future:
The semantics of Java arrays and JavaScript arrays are different - Java arrays cannot be resized, and are initialized with specific values based on the component type (the data in the array). Since you are writing Java code, the compiler could conceivable make assumptions based on details about how you create and use that array that could be broken by JS code that doesn't know to never modify the array.
Some arrays of primitive types could be optimized into TypedArrays in JavaScript, more closely following Java semantics in terms of resizing and Java behavior in terms of allocation. This would be a performance boost as well, but could break any use of int[], double[], etc.
Instead, you should copy your data into a JsArrayString, or just use the js array to hold the data rather than going back and forth, depending on your use case. The various JsArray types can be resized and already exist as JavaScript objects that outside JS can understand and work with.
Reply to EDIT 2:
At a guess, the parallel.js script is trying to run your code from another scope such a in the webworker (that's the point of the code, right) where your GWT code isn't present. As such, it can't call the makeJavaInvoke which is the bridge back into dev mode (would be a different failure with compiled JS). According to http://adambom.github.io/parallel.js/ there are specific requirements that a passed callback must meet to be passed in to spawn and perhaps then - your anonymous functions definitely do not meet them, and it may not be possible to maintain java semantics.
Before I get much deeper, check out this answer I did a while ago addressing the basic issues with webworkers and gwt/java: https://stackoverflow.com/a/11376059/860630
As noted there, WebWorkers are effectively new processes, with no shared code or shared state with the original process. The Parallel.js code attempts to paper over this with a little bit of trickery - shared state is only available in the form of the contents passed in to the original Parallel constructor, but you are attempting to pass in instances of 'java' objects and calling methods on them. Those Java instances come with their own state, and potentially can link back to the rest of the Java app by fields in the Worker instance. If I were implementing Worker and doing something that referenced other data than what was passed in, then I would be seeing further bizarre failures.
So the functions you pass in must be completely standalone - they must not refer to external code in any way, since then the function can't be passed off to the webworker, or to several webworkers, each unaware of each other's existence. See https://github.com/adambom/parallel.js/issues/32 for example:
That's not possible since it would
require a shared state across workers
require us to transmit all scope variables (I don't think there's even a possibility to read the available scopes)
The only thing which might be possible would be cache variables, but these can already be defined in the function itself with spawn() and don't make any sense in map (because there's no shared state).
Without being actually familiar with how parallel.js is implemented (all of this answer so far is reading the docs and a quick google search for "parallel.js shared state", plus having experiemented with WebWorkers for a day or so and deciding that my present problem wasn't yet worth the bother), I would guess that then is unrestricted, and you can you pass it whatever you like, but spawn, map, and reduce must be written in such a way that their JS can be passed off to the new JS process and completely stand alone there.
This may be possible from your normal Java code when compiled, provided you have just one implementation of Worker and that impl never uses state other than what is directly passed in. In that case the compiler should rewrite your methods to be static so that they are safe to use in this context. However, that doesn't make for a very useful library, as it seems you are trying to achieve. With that in mind, you could keep your worker code in JSNI to ensure that you follow the parallel.js rules.
Finally, and against the normal GWT rules, avoid $entry for calls you expect to happen in other contexts, since those workers have no access to the normal exception handling and scheduling that $entry enables.
(and finally finally, this is probably still possible if you are very careful at writing Worker implementations and write a Generator that invokes each worker implementation in very specific ways to make sure that com.google.gwt.dev.jjs.impl.MakeCallsStatic and com.google.gwt.dev.jjs.impl.Pruner can correctly act to knock out the this in those instance methods once they've been rewritten as JS functions. I think the cleanest way to do this is to emit the JSNI in the generator itself, call a static method written in real Java, and from that static method call the specific instance method that does the heavy lifting for spawn, etc.)
I am a newcomer to GWT and JavaScript.
There are similar question of this type I have tried to follow, but I keep failing.
I have a GWT app, I need to call a Java function from Javascript( on the onclick of a href tag, in particular.) Following is what I have done.
public class JSNITest {
public static void handleAnchorClick(int a , int b) {
Window.alert("Current row and Column is " + a + " " + b);
}
public static native void exportMyFunction()/*-{
$wnd.handleAnchorClick = function(param1,param2){
#company.package.class.JSNITest::handleAnchorClick(*)(param1,param2);
}-*/;
}
And in the HTML,
link
(a1 , a2) are two integer variables in my code.
I have also called EnclosingClass.exportMyFunction() in the entry point function.
I keep running into various kinds of exceptions(No Such class exception). Can someone please correct me?
Regards
Let me explain a bit more about exporting GWT stuff to the JS world. You have several options to do that, but I will focus on three methods.
[EDITED]
0- JsInterop: GWT maintainers are working in a new feature to easily export java methods to javascript, and wrap javascript objects. The feature was very experimental in 2.7.0 lacking some features, but in 2.8.0 will be almost functional. Please take a look to the Design Document, and other discussions in the mailing list.
[END]
1- JSNI: The first one is to write your own jsni, in this case you have to be aware about the possible mistakes you could make. Basically these mistakes are because you have to know how to deal with types. In your case if you want to get a javascript array (like you are asking in your comment below), the solution could be:
public static native void exportMyFunction()/*-{
$wnd.handleAnchorClick = #company.package.class.JSNITest::handleAnchorClick(*);
}-*/;
public static void handleAnchorClick(JsArrayMixed args) {
Window.alert("Current row and Column is " +
args.getNumber(0) + " " + args.getNumber(1));
}
public void onModuleLoad() {
exportMyFunction();
}
//javascript code
window.handleAnchorClick([1,2])
Note that JSNI only allows you to pass primitive types (except long) and JavaScriptObject objects. So when passing a javascript array, you have to receive it with a JavaScriptObject like in the example. In this case, since javascript only uses a type for numbers, args.getNumber will return always a double, and you have to convert in java.
2- gwt-exporter For exporting large projects, or when you need to handle complex objects and classes I'd rather use gwt-exporter
static class MyClass implements Exportable {
#Export("$wnd.handleAnchorClick")
public static void handleAnchorClick(double[] args) {
Window.alert("Current row and Column is " +args[0] + " " + args[1]);
}
}
public void onModuleLoad() {
GWT.create(MyClass.class);
}
//javascript code
window.handleAnchorClick([1,2])
gwt-exporter will deal with any kind of primitive types (even with long) myfunc(long[] args), with var-args myfunc(long...args), it supports method overload, and much more.
3- gwtquery Finally if you prefer gwtquery, you can use a technique to add function properties to any js object like window
// The GQuery Properties object is able to wrap a java Function object
// into an js property.
Properties wnd = window.cast();
wnd.setFunction("handleAnchorClick", new Function() {
public void f() {
// Get the js arguments[] array
JsArrayMixed args = arguments(0);
// Get the first element of the arguments[] array
JsArrayMixed ary = args.getObject(0);
Window.alert("Current row and Column is " +
ary.getNumber(0) + " " + ary.getNumber(1));
}
});
//javascript code
window.handleAnchorClick([1,2])
With gquery you can use the gwt JsArrayMixed class which always returns a number as a double, or you can use a JsCache which allows to convert numbers to any other numeric type in java ((JsCache)ary.get(1, Integer.class)
As a summary, I would rather use gwt-exporter as the first option because it is specialized in handling this problematic. As a second option, I would use gquery which is a serious complement to gwt. Finally, I would avoid to use hand-written jsni when possible, Javascript is normally a source of issues and mistakes (think that the main goal of gwt is not to deal with js).
You should consider GWT exporter. You might even consider waiting because GWT 2.8 should come out pretty soon. It was supposed to come out some time around The begging of 2015. 2015 has already begun and they're demonstrating at GWT.create right now so it should come out any day now. If you can't wait then you can either use experimental is interop, JSNI like the top answer says to or GWT exporter. JSNI is more complicated and involves a lot of boiler plate code so if you have to do a lot of js interop I recommend GWT-exporter.
In my app I use JsArray extensively to store my overlay types. I use java.util.List to store my client-side Java POJOs.
For performance reasons and to unify the way I access my model I planned to eliminate the Lists and use only JSO wrappers. Given a wrapper around a native array that can store any Java Object:
public class JsArrayObject<T> extends JavaScriptObject {
protected JsArrayObject() {}
public final native T get(int index) /*-{
return this[index];
}-*/;
public final native void push(T value) /*-{
this[this.length] = value;
}-*/;
}
Is it safe to store Java Objects this way? The doc says that when you pass a Java Object into JavaScript the result is "an opaque value accessible through special syntax". This sounds confussing to me. For instance if I push an Integer and try to get it an exception will be thrown because something different than an Object was found (at least in dev mode). The same happens with the rest of Java primitive Wrappers. Apart from the problems with Java primitive Wrappers, are there other concerns to be aware?
Many thanks
Which doc are you referring to? The one on this page?
They're talking in terms of passing Java objects into JavaScript with the intent of having JavaScript code use the methods or fields in the object. It is possible to do that, but the syntax you have to use on the JavaScript side is a bit awkward. If you've done any JSNI, you've seen it.
If you don't intend to access the Java objects from the JavaScript side you can ignore the business about the special syntax. So yes, it is safe. I'd be interested to know if it actually turns out to help performance.