I am trying to return the result of a calculation from an RPC call, and
having trouble with the GWT compiler. Specifically, the class I am
returning has a field of type Object in it. This field can contain:
String, Integer, Double, Long, Boolean or Date.
If I change the Object field to type String, the compiler is happy.
The thing that has me stumped is that I have other methods in the same RPC
service that return similar objects containing Object fields and these are
working correctly. I also have an RPC-based event mechanism that is
returning event classes that contain Map<String,Object> and these appear to
work correctly. I of course have to have another interface (a whitelist)
that refers to the types I want to return in the Object fields to get
serialization code generated for those types.
Am I doing something wrong? I see the documentation says I can't return
Object, but it's been working for a couple of years.
Is there a better way to accomplish this?
Here's the class of the object I'm trying to return:
public class CalculationResult implements Serializable {
private static final long serialVersionUID = 1L;
private Object value = null;
private PropertyType type;
private List<LocalizedMessage> errors;
public CalculationResult() {
super();
}
public Object getValue() {
return value;
}
public void setValue(Object value) {
this.value = value;
}
public PropertyType getType() {
return type;
}
public void setType(PropertyType type) {
this.type = type;
}
public List<LocalizedMessage> getErrors() {
if( this.errors == null ) {
this.errors = new ArrayList<LocalizedMessage>();
}
return this.errors;
}
public void setErrors(List<LocalizedMessage> errors) {
this.errors = errors;
}
}
PropertyType is a simple enum.
LocalizedMessage is a serializable class containing only String and
List<String> fields and is used extensively in other RPC calls.
When I compile my project with GWTC, I get the following:
[java] Compiling module com.XX.XXXXXXXXXXXXXXXXXXXXXXXXXXx
[java] Computing all possible rebind results for
'com.XX.gwt.ui.client.rpc.PMRPCService'
[java] Rebinding com.XX.gwt.ui.client.rpc.PMRPCService
[java] Invoking generator
com.google.gwt.user.rebind.rpc.ServiceInterfaceProxyGenerator
[java] Generating client proxy for remote service
interface 'com.XX.gwt.ui.client.rpc.PMRPCService'
[java] Checking type argument 0 of type
'java.util.Arrays.ArrayList<E>' because it is exposed as an array with a
maximum dimension
of 1 in this type or one of its subtypes (reached via com.XX
.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.gwt.editor.client.adapters.ListEditorWrapper<T, E> is not
default instantiable (it must have a zero-argu
ment constructor or no constructors at all) and has no custom serializer.
(reached via com.XX.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.gwt.user.client.ui.DelegatingChangeListenerCollection is not
default instantiable (it must have a zero-a
rgument constructor or no constructors at all) and has no custom
serializer. (reached via com.XX
.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.gwt.user.client.ui.DelegatingClickListenerCollection is not
default instantiable (it must have a zero-ar
gument constructor or no constructors at all) and has no custom serializer.
(reached via com.XX.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.gwt.user.client.ui.DelegatingFocusListenerCollection is not
default instantiable (it must have a zero-ar
gument constructor or no constructors at all) and has no custom serializer.
(reached via com.XX.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.gwt.user.client.ui.DelegatingKeyboardListenerCollection is not
default instantiable (it must have a zero
-argument constructor or no constructors at all) and has no custom
serializer. (reached via com.XX
.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.gwt.view.client.ListDataProvider<T>.ListWrapper<> is not default
instantiable (it must have a zero-argum
ent constructor or no constructors at all) and has no custom serializer.
(reached via com.XX.core.resources.calculation.CalculationResult)
[java] [ERROR]
com.google.web.bindery.autobean.shared.impl.SplittableList<E> is not
default instantiable (it must have a zero-argu
ment constructor or no constructors at all) and has no custom serializer.
(reached via com.XX.core.resources.calculation.CalculationResult)
[java] [ERROR] java.util.AbstractList.SubList<E> is not
default instantiable (it must have a zero-argument constructor or no const
ructors at all) and has no custom serializer. (reached via com.XX
.core.resources.calculation.CalculationResult)
[java] [ERROR]
java.util.Collections.UnmodifiableList<T> is not default instantiable (it
must have a zero-argument constructor or
no constructors at all) and has no custom serializer. (reached via com.XX
.core.resources.calculation.CalculationResult)
[java] [ERROR]
java.util.Collections.UnmodifiableRandomAccessList<T> is not default
instantiable (it must have a zero-argument con
structor or no constructors at all) and has no custom serializer. (reached
via com.XX.core.resources.calculation.CalculationResult)
[java] [ERROR] Errors in
'com/XX/gwt/ui/client/ClientFactoryImpl.java'
[java] [ERROR] Line 327: Failed to resolve
'com.XX.gwt.ui.client.rpc.PMRPCService'
via deferred binding
This error seems to be having trouble with the list, but if I simply remove
the Object field or change it to String, these go away, too.
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