GWT serialization issue while doing RPC

Question

i am learning GWT.

I got a error regarding the serilizablity.

breif discription of my problem

In class Customproperties

package com.exp.shared;


import java.io.Serializable;
import java.util.List;

public class Customproperties implements Serializable  {

    private Object value;
    private List<?> values;
          // more variable

    public Customproperties() {
        // TODO Auto-generated constructor stub
    }

    public Customproperties(String propertyName, List<?>  object,
            String propertyType, boolean mulitiValued, String cardinality, Boolean required) {

        this.propertyName=propertyName;
        this.values=object;
                // more initialization
    }

    public Customproperties(String propertyName,  List<?> object, String propertyType,
            boolean multiValued) {
        this.propertyName=propertyName;
        this.values=object;
                // more initialization
    }

    public Object getValue() {
              return value;
    }
    public List<?> getValues() {
        return values;
    }
 }

In server package in one of the classImpl i am using a object of Customproperties

      if (doc.getPropertyValue("cmis:objectTypeId").toString().equals("cmis:document")) {

    customproperty=new Customproperties(p.getDefinition().getDisplayName(), p.getValue(), p.getType().toString(),p.isMultiValued());
       }
else {
    customproperty=new Customproperties(p.getDefinition().getDisplayName(), p.getValues(), p.getType().toString(),p.isMultiValued(),value.getCardinality(),value.isRequired());
            }

here in if condntion p.getValue() returns Object. and in else condition p.getValues() returns List.

in CustomProperties class when i change the object variable to string it is working perfectly fine.

but i dont change it it gives me error.

com.exp.shared.Customproperties' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.exp.shared.Customproperties@1aa5344
        at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:619)

I dont want to change it String . i just want to receive Object. cause this object can be some times String , date , int .

Plzz help.

Answer 1

You should read the GWT docs about RPC serialization here .

The class java.lang.Object is not serializable, therefore you cannot expect that a collection of Object types will be serialized across the wire.

This is why you get your exception. In the code you've given, you're not using the field value. Both constructors on your class only set the values list. So if you're not using the field value, just remove it and it will work. But assuming that's a mistake and you do need to use it ...

You will have to know all the different possible types your value can have. And then either you have different fields, like intValue, dateValue, stringValue ... Or you can have one String field, and serialize your objects into strings like this.

public class CustomProperties {
    private String value;
    private String type;

    private void setValue(Object value, String type) {
        if (value != null) {
            this.value = value.toString();
            this.type = type;
        }
    }

    private Object getValue() {
        if (value != null) {
            if ("int".equals(type)) return Integer.valueOf(value);
            elseif ("date".equals(type)) return // Parse date from value here
            elseif ("string".equals(type)) return (String) value;
            // other cases
        }
        return value;
    }

}

Answer 2

In GWT when declaring containers never declare generic types like List .
Always use the more specific types like ArrayList .

Answer 3

In your case, the problem is most likely the List<?> . GWT doesnt know what possible types you are putting in that list, so instead of generating code to serialize every single possible type on the sourcepath, it generates nothing except for what it knows it already needs. When you attempt to put something in there that wasn't needed elsewhere, the exception occurs, indicating that GWT wasn't told that you planned on sending that object over the wire.

A standard approach here is usually to create a marker interface that probably implements Serializable , and make it a List<MyModelObjects> . Then every object that can fit in there should implement that interface.