Bug reports and feature request: Genson 0.94

[jens.ha...@gmail.com]

Hi Eugen,

first of all: thanks for creating this fantastic tool. I am trying to serialize very heterogeneous polymorphic objects, and where flexjson and jackson left me stranded, genson picked up.

However, I noticed a few issues, which create very unexpected errors. Please let me know if you need more detail on any of these.

1. [Bug] A class that has a "setter" with an empty parameter list leads to an exception during serialization.

Example:

class Foo {
    Integer bar;

    Integer getBar() {
        return bar;
    }

    void setBar(Integer bar) {
        this.bar = bar;
    }

    /* erroneously considered to be a setter */
    void setToNull() {
        this.bar = null;
    }
}

java.lang.ArrayIndexOutOfBoundsException: 0
    at com.owlike.genson.Genson$Builder$2.isMutator(Genson.java:799)
    at com.owlike.genson.reflect.BeanMutatorAccessorResolver$CompositeResolver.isMutator(BeanMutatorAccessorResolver.java:166)
    at com.owlike.genson.reflect.BaseBeanDescriptorProvider.provideMethodMutators(BaseBeanDescriptorProvider.java:264)
    at com.owlike.genson.reflect.BaseBeanDescriptorProvider.provideBeanPropertyMutators(BaseBeanDescriptorProvider.java:102)
    at com.owlike.genson.reflect.AbstractBeanDescriptorProvider.provide(AbstractBeanDescriptorProvider.java:51)
    at com.owlike.genson.convert.BasicConvertersFactory.provide(BasicConvertersFactory.java:109)
    at com.owlike.genson.convert.BasicConvertersFactory.create(BasicConvertersFactory.java:74)
    at com.owlike.genson.convert.BasicConvertersFactory.create(BasicConvertersFactory.java:56)
    at com.owlike.genson.convert.ChainedFactory.create(ChainedFactory.java:93)
    at com.owlike.genson.convert.ChainedFactory.create(ChainedFactory.java:80)
    at com.owlike.genson.convert.ChainedFactory.create(ChainedFactory.java:93)
    at com.owlike.genson.convert.ChainedFactory.create(ChainedFactory.java:80)
    at com.owlike.genson.convert.CircularClassReferenceConverterFactory.create(CircularClassReferenceConverterFactory.java:58)
    at com.owlike.genson.convert.CircularClassReferenceConverterFactory.create(CircularClassReferenceConverterFactory.java:22)
    at com.owlike.genson.Genson.provideConverter(Genson.java:182)
    at com.owlike.genson.Genson.serialize(Genson.java:279)
    at com.owlike.genson.Genson.serialize(Genson.java:207)

Current workaround: "Mask out" the offending setXXX method, like so:
    Genson genson = new Genson.Builder().exclude("toNull");

Suggested fix: In the isMutator method, check for the size of the parameter list and return false, so setToNull is (rightfully) no longer considered a setter.

2. [Bug] A class with a generic that implements Comparable (a fairly common case) leads to a stack overflow during deserialization, because of the self-referential generic type.

class Interval<T extends Comparable<T>> {
    T min;
    T max;
    public T getMin() { return min;}

    public T getMax() { return max;}

    public void setMin(T min) { this.min = min; }

    public void setMax(T max) { this.max = max; }
}

com.owlike.genson.TransformationException: Could not deserialize to property 'signatures' of class class ca.mda.sva.common.domain.alerts.AlertDuplicateIdentity
    at com.owlike.genson.reflect.PropertyMutator.couldNotDeserialize(PropertyMutator.java:58)
    at com.owlike.genson.reflect.PropertyMutator.deserialize(PropertyMutator.java:41)
    at com.owlike.genson.reflect.BeanDescriptor.deserialize(BeanDescriptor.java:116)
    at com.owlike.genson.reflect.BeanDescriptor.deserialize(BeanDescriptor.java:98)
    at com.owlike.genson.convert.ClassMetadataConverter.deserialize(ClassMetadataConverter.java:103)
    at com.owlike.genson.convert.NullConverter$NullConverterWrapper.deserialize(NullConverter.java:61)
    at com.owlike.genson.convert.ClassMetadataConverter.deserialize(ClassMetadataConverter.java:95)
    at com.owlike.genson.convert.NullConverter$NullConverterWrapper.deserialize(NullConverter.java:61)
    at com.owlike.genson.Genson.deserialize(Genson.java:331)
    at com.owlike.genson.Genson.deserialize(Genson.java:296)
Caused by: java.lang.StackOverflowError
    at sun.reflect.generics.reflectiveObjects.TypeVariableImpl.hashCode(Unknown Source)
    at com.owlike.genson.reflect.TypeUtil$TypeAndRootClassKey.<init>(TypeUtil.java:467)
    at com.owlike.genson.reflect.TypeUtil.expandType(TypeUtil.java:56)
    at com.owlike.genson.reflect.TypeUtil.expandType(TypeUtil.java:66)
    at com.owlike.genson.reflect.TypeUtil.expandType(TypeUtil.java:90)
    at com.owlike.genson.reflect.TypeUtil.expandType(TypeUtil.java:66)
    at com.owlike.genson.reflect.TypeUtil.expandType(TypeUtil.java:90)
    at com.owlike.genson.reflect.TypeUtil.expandType(TypeUtil.java:66)
    ....

Note: expandType() is alternately called with type=Comparable<T> and type=T.

Current workaround: Create a marker class that instantiates T with a concrete type, for each instantiating class for T used in any type to be serialized (ugly, but works for me for the time being).

Suggested fix: To break the self-referentiality, create the ExpandedParameterizedType first, and keep a HashMap of mappings
Type->corresponding ExpandedType. Don't include the type args in the constructor, but recursively expand the type arguments first,
then set them via a setter setTypeArgs(Type[] typeArgs).
Upon re-encountering the previously encountered type T (or perhaps Comparable<T>) in the recursion, close the loop by referring to the already created ExpandedParameterizedType.
(Of course, this means that you now have a circular link in your ExpandedParameterizedType hierarchy, and I am not sure what that will do to your deserialization code.)

3. [Feature Request] Allow Genson to serialize any map (currently, only HashMaps whose keys are strings are supported).

My workaround is to create a ConverterFactory for a Map<K,V>, whose converter serializes a map into an array of key-value pairs, like so:

Java:

package my.package;
HashMap<MyKeyClass, MyValueClass> myMap;

Json:

"myMap":{
  "@class":"java.util.HashMap",
  "map":[
    {"key":{"@class":"my.package.MyKeyClass","arg1":val1,"arg2":val2,...},
    "value":{"@class":"my.package.MyValueClass","arg3":val3,"arg4":val4,...}},
    ...
    {"key":{"@class":"my.package.MyKeyClass","arg1":val11,"arg2":val22,...},
    "value":{"@class":"my.package.MyValueClass","arg3":val33,"arg4":val44,...}}]}

I could make this ConverterFactory available.

[Eugen Cepoi]

2013/2/23 <jens.ha...@gmail.com>

Hi Eugen,

first of all: thanks for creating this fantastic tool.

Thanks :)
 

Bug fixed.
 

Yeah this is what I have done for self referencing classes in CircularClassReferenceConverterFactory, but the problem was a bit different.
Here it can happen only with generic types with their expanded representation being their upper bound. I think maybe using the rawClass of their expanded form (the upper bound) should do the work. Its what I have implemented in TypeUtil, the corresponding test cases are testCyclicGenericTypes and testGenericCyclicTypes.
 
Could you try it and confirm if it is OK? The changes are available in the repo.

3. [Feature Request] Allow Genson to serialize any map (currently, only HashMaps whose keys are strings are supported).

My workaround is to create a ConverterFactory for a Map<K,V>, whose converter serializes a map into an array of key-value pairs, like so:

Java:

package my.package;
HashMap<MyKeyClass, MyValueClass> myMap;

Json:

"myMap":{
  "@class":"java.util.HashMap",
  "map":[
    {"key":{"@class":"my.package.MyKeyClass","arg1":val1,"arg2":val2,...},
    "value":{"@class":"my.package.MyValueClass","arg3":val3,"arg4":val4,...}},
    ...
    {"key":{"@class":"my.package.MyKeyClass","arg1":val11,"arg2":val22,...},
    "value":{"@class":"my.package.MyValueClass","arg3":val33,"arg4":val44,...}}]}

Hum why not, this looks like a good solution. But I am not sure about the format, maybe : "myMap" : [ {"key": {}, "value": {}}, ...] ?
Downside it does not represent a map as a json object and class metadata would not be available (works only on json objects), on the other side it looks cleaner.
 

I could make this ConverterFactory available.

Great contributions are welcome :) google code doesn't support pull requests, but you can open an issue and attach your feature.
When all 3 points are validated I will release a new version.
 

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