Java – Error: Class declares multiple JSON fields named serialVersionUid

androidgsonjavajsonserialization

I have class A, that extends class B, that implements Serializable.

When i try to transform it in a JSON, using GSON lib, it says that "class declares multiple JSON fields named serialVersionUid".

As long as i know, if i don't explicit declare serialVersionUid, it is generated by GSON.

I also tried to put serialVersionUid statically, but doesn't work.

I can fix the error by implementing Serialization in class A, but i have many classes that extends B, and i don't think exclude B from them will be a good ideia…

Does anyone know why this error occurs?

Class A extends B {
    private c;
    private d;
    private e;
}

Class B extends Serializable{
    private f;
    private g;
}

Best Answer

EDITED:

We've changed the code there to use GSON with a customised GsonBuilder class. The code is looking a little bit like that:

...
private static final List<String> EXCLUDE = new ArrayList<String>() {{
    add("serialVersionUID");
    add("CREATOR");
}};
....
Gson gson = new GsonBuilder()
            .excludeFieldsWithModifiers(Modifier.TRANSIENT)
            .setExclusionStrategies(new ExclusionStrategy() {
                @Override
                public boolean shouldSkipField(FieldAttributes f) {
                    boolean exclude = false;
                    try {
                        exclude = EXCLUDE.contains(f.getName());
                    } catch (Exception ignore) {
                    }
                    return exclude;
                }

                @Override
                public boolean shouldSkipClass(Class<?> clazz) {
                    return false;
                }
            })
            .create();
return gson.toJson(object);

In this case, we're ignoring the serialVersionUID and the CREATOR fields when jsonizing it.

OLD:

I had the same issue some seconds ago. I've solved it by adding serialVersionUUID using the transient modifier. to by superclass, like that:

private transient static final long serialVersionUID = 1L;

I hope it helps you too.

Related Solutions

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Python – How to make a class JSON serializable

Here is a simple solution for a simple feature:

`.toJSON()` Method

Instead of a JSON serializable class, implement a serializer method:

import json

class Object:
    def toJSON(self):
        return json.dumps(self, default=lambda o: o.__dict__, 
            sort_keys=True, indent=4)

So you just call it to serialize:

me = Object()
me.name = "Onur"
me.age = 35
me.dog = Object()
me.dog.name = "Apollo"

print(me.toJSON())

will output:

{
    "age": 35,
    "dog": {
        "name": "Apollo"
    },
    "name": "Onur"
}

Best Answer

Related Solutions

Java – How to test a class that has private methods, fields or inner classes

Python – How to make a class JSON serializable

.toJSON() Method

Related Topic

`.toJSON()` Method