Java对象可以通过GWT中的Javascript访问吗？ [英] Can Java objects be accessed from Javascript in GWT?

问题描述

我的目标是直接从JavaScript启动RPC调用。我想出了一些假回调方法（由于RPC的异步性质），但我无法弄清楚如何将自定义对象转换为javascript。

所以，我创建了一个名为Interop的类，并静态创建了我感兴趣的服务（必须使用静态，因为这是我所能工作的一切，我不认为它现在是相关的）：

  public class Interop {
 private static final GreetingServiceAsync service = GWT .create（GreetingService.class）; 
 ... 
} 
  

然后创建一个函数，异步调用和处理响应：

$ p $ public static void greetServer（final String success，final String failure）{
service .greetServer（
Homer，
新的AsyncCallback< String>（）{
public void onFailure（Throwable caught）{
callback（failure，caught.toString（））;

$ b public void onSuccess（String result）{
callback（success，result）;
}
}
）;





$ b然后我创建了一个JSNI函数将这个函数导出为javascript， onModuleLoad（）：



  public static native void export（）/ *  -  {
 $ wnd.greetServer = $条目（@ package.Interop :: greetServer（Ljava /郎/字符串; Ljava /郎/字符串;））; 
}  -  * /; 
  

另外创建另一个JSNI函数来处理回调：



  public static native callback（String func，String response）/ *  -  {
 $ wnd [func]（response）; 
}  -  * /; 
  

为了成功和失败，最初传递给greetServer（）的函数名称由JSNI调用作为回调。当处理字符串或（我假设）一个原始类型时，这一切都很好。但是，当我尝试使用自定义类型执行此操作时（请注意已更改的Custom类型参数）：



  public static native void callback（String func，Custom response）/ *  -  {
 $ wnd [func]（response）; 
}  -  * /; 
  

然后，javascript中的内容不起作用。它似乎是一个带有层叠数组的javascript对象，并且这些方法都不可用。

所以，问题是，Java初始化对象不是基本的或基元可以从JavaScript（而不是JSNI）中访问？从我可以告诉JavaScriptObject需要源于JavaScript，但在我的情况下，我的对象来自Java。我可以做什么？

我也研究过gwt-exporter，它展示了如何从javascript实例化java的东西，但不知道如何访问java发起的东西javascript。

我知道这有点令人困惑，所以如果您有任何问题，请让我知道。

解决方案

使用gwt-exporter这可能是您的代码：

  //创建并导出用于包装javascript回调的闭包
 @ExportClosure 
 public static interface InteropCallback extends Exportable {
 void exec（String message） ; 
} 
 
 //在其中创建Interop类的可导出和导出方法
 @ExportPackage（foo）
 @Export 
 public static class Interop实现Exportable {
最终静态GreetingServiceAsync服务= GWT.create（GreetingService.class）; 
 
 public static void greeting（String message，$ b $ final InteropCallback success，
 InteropCallback error）{
 service.greetServer（message，new AsyncCallback< String>（） {
 public void onFailure（Throwable caught）{
 error.exec（caught.getMessage（））; 
} 
 public void onSuccess（String result）{
 success .exec（result）; 
} 
}）; 
 
 
 
在你的onModuleLoad中，你必须让gwt-exporter导出你的东西
 @Override public void onModuleLoad（）{
 ExporterUtil .exportAll（）; 
 ... 
} 
  

最后从手写javascript

  window.foo.Interop.greeting（Hello，
 function（s）{console.log（s） }，
函数（s）{console.log（s）} 
）; 
  

My goal is to initiate RPC calls directly from javascript. I have come up with ways to fake callbacks (because of the asynchronous nature of RPC) but I can't figure out how to get custom objects into javascript.

So, I've created a class named Interop and I statically create the service I'm interested in (had to use static as it was all I could get working, I don't think it's relevant right now):

public class Interop {
    private static final GreetingServiceAsync service = GWT.create(GreetingService.class);
    ...
}

I then create a function that will do the async calls and handle the responses:

public static void greetServer(final String success, final String failure) {
    service.greetServer(
        "Homer", 
        new AsyncCallback<String>() {
            public void onFailure(Throwable caught) {
                callback(failure, caught.toString());

            }
            public void onSuccess(String result) {
                callback(success, result);
            }
        }
    );
}

Then I create a JSNI function to export this function to javascript which I call from the onModuleLoad():

public static native void export() /*-{
    $wnd.greetServer = $entry(@package.Interop::greetServer(Ljava/lang/String;Ljava/lang/String;));
}-*/;

And also create another JSNI function to deal with the callbacks:

public static native void callback(String func, String response) /*-{
    $wnd[func](response);
}-*/;

So that the function names I pass into greetServer() initially for success and failure are called by the JSNI as callbacks. And this all works great when dealing with Strings or (I assume) a primitive type. But when I try to do this with custom types (note the altered Custom type parameter):

public static native void callback(String func, Custom response) /*-{
    $wnd[func](response);
}-*/;

Then what ends up in javascript doesn't work. It seems to be a javascript object with cascading arrays and none of the methods are available.

So, the question is, how can Java-originated objects that aren't basic or primitives be accessed from within javascript (not JSNI)? From what I can tell JavaScriptObject needs to originate in javascript, but in my case, my objects are originating in Java. What can I do?

I've also looked into gwt-exporter and that shows how to instantiate java stuff from javascript, but not how to access java-originated stuff in javascript.

I know this is a bit confusing so please let me know if you have any questions. Thanks!

解决方案

With gwt-exporter this could be your code:

// Create and export a closure used to wrap javascript callbacks
@ExportClosure
public static interface InteropCallback extends Exportable {
  void exec(String message);
}

// Make your Interop class exportable and export methods in it
@ExportPackage("foo")
@Export
public static class Interop implements Exportable {
  final static GreetingServiceAsync service = GWT.create(GreetingService.class);

  public static void greeting(String message, 
                              final InteropCallback success,
                              final InteropCallback error) {
    service.greetServer(message, new AsyncCallback<String>() {
      public void onFailure(Throwable caught) {
        error.exec(caught.getMessage());
      }
      public void onSuccess(String result) {
        success.exec(result);
      }
    });
  }
}

// In your onModuleLoad you have to make gwt-exporter export your stuff
@Override public void onModuleLoad() {
  ExporterUtil.exportAll();
  ...
}

Finally call your java methods from handwritten javascript

window.foo.Interop.greeting("Hello", 
                            function(s){console.log(s)},
                            function(s){console.log(s)}
                            );

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