Thursday, December 15, 2016

Re: Strange ClassCastException with GWT 2.8 and SDM

Hi Kirill,

Yes, I know, but I think it a bit strange that this only happens on direct accessing the model and not when I assign the value to a variable and use String.valueOf on this. 

GXT uses internally their FastMap, a HashMap that is based on JSNI if running on the client. This seems to be the problem.

BTW, I switched to GWT 2.7.0 and the problem disappears. So there's something in GWT 2.8.0 that triggers the problem. 

Thanks anyway


Am Mittwoch, 14. Dezember 2016 17:53:03 UTC+1 schrieb Kirill Prazdnikov:

It seems here you are trying to cast a native js object to java type. 

Sometimes GWT generates ClassCastException when I cast type "@JsType(isNative=true) A" to type B which is also native type. This is also kind of magic for me and I also have a strange workaround: write a native method that does the cast by "return arg".  

I wrote about that earlier:


среда, 14 декабря 2016 г., 19:29:39 UTC+3 пользователь Norbert Bartels написал:

Hi all,

I'm migrating our GWT app to GWT 2.8 as a PoC because we like to use the SDM.

While testing the SDM I see some strange ClassCastExceptions in the console.

We use gxt 2 and changed some things to make it work with GWT > 2.5.1.

Here's the error message (stacktrace) of the the class cast exception:

java.lang.ClassCastException      at Unknown.java_lang_Throwable_Throwable__V(Unknown Source)      at Unknown.java_lang_Exception_Exception__V(Unknown Source)      at Unknown.java_lang_RuntimeException_RuntimeException__V(Unknown Source)      at Unknown.java_lang_ClassCastException_ClassCastException__V(Unknown Source)      at Unknown.javaemul_internal_InternalPreconditions_checkCriticalType__ZV(Unknown Source)      at Unknown.javaemul_internal_InternalPreconditions_checkType__ZV(Unknown Source)      at Unknown.com_google_gwt_lang_Cast_castTo__Ljava_lang_Object_2Lcom_google_gwt_core_client_JavaScriptObject_2Ljava_lang_Object_2(Unknown Source)      at Unknown.com_extjs_gxt_ui_client_widget_treegrid_TreeGridCellRenderer_getText__Lcom_extjs_gxt_ui_client_widget_treegrid_TreeGrid_2Lcom_extjs_gxt_ui_client_data_ModelData_2Ljava_lang_String_2IILjava_lang_String_2(Unknown Source)      at Unknown.com_extjs_gxt_ui_client_widget_treegrid_TreeGridCellRenderer_render__Lcom_extjs_gxt_ui_client_data_ModelData_2Ljava_lang_String_2Lcom_extjs_gxt_ui_client_widget_grid_ColumnData_2IILcom_extjs_gxt_ui_client_store_ListStore_2Lcom_extjs_gxt_ui_client_widget_grid_Grid_2Ljava_lang_Object_2(Unknown Source)    ...  

The code that triggers this exception is this (

return String.valueOf(model.get(property));  

My temporary solution to fix this is:

Object obj = model.get(property);  String.valueOf(obj);  

I already found several places where the class cast exception occurs and where this fix solves the problem, but I'm afraid that there's something going wrong somewhere in GWT.


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