getting a StackOverflow while trying to serialize domain objects in Grails

[Brian Bonner]

I've logged a bug over on the Grails side of things along w/ a test case at http://jira.grails.org/browse/GRAILS-9127?focusedCommentId=71108#comment-71108

Basically, I'm trying to use Grails map based constructors to create objects.  I have a test case where I populate Domain objects using the constructor and when I check the values on the object, they're populated correctly.

For some reason however, my test fails as soon as I try to serialize Operations using Gson.   I'm using Gson 2.2.1.

Can anyone shed some light on why this might be happening?   The code works with Java and Groovy so I would think it would be related to how Grails is constructing objects using the constructor, but I don't seem to see anything wrong there.   It's almost as if it's struggling with the types involved.

Any help would be appreciated.

java.lang.StackOverflowError
at sun.misc.FpUtils.getExponent(FpUtils.java:130)
at java.lang.Math.getExponent(Math.java:1295)
at java.lang.StrictMath.floorOrCeil(StrictMath.java:338)
at java.lang.StrictMath.floor(StrictMath.java:323)
at java.lang.Math.floor(Math.java:407)
at sun.misc.FloatingDecimal.dtoa(FloatingDecimal.java:601)
at sun.misc.FloatingDecimal.<init>(FloatingDecimal.java:440)
at java.lang.Double.toString(Double.java:179)
at java.lang.String.valueOf(String.java:2973)
at java.lang.Double.toString(Double.java:603)
at com.google.gson.stream.JsonWriter.value(JsonWriter.java:480)
at com.google.gson.Gson$4.write(Gson.java:266)
at com.google.gson.Gson$4.write(Gson.java:251)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
at com.google.gson.internal.bind.ObjectTypeAdapter.write(ObjectTypeAdapter.java:105)

[Inderjeet Singh]

Gson would throw a StackOverflow if you have circular references. Could that be the reason?

Inder

http://www.singhinderjeet.com/

[Brandon Mintern]

If you don't need to de/serialize inner classes, you can configure
your GsonBuilder with disableInnerClassSerialization() to avoid
problems like this.

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[Brian Bonner]

nope, no circular references.

[Brian Bonner]

Brandon doing this doesn't change the results.  I still get a stack overflow.

Here's my classes and my test:

@EqualsAndHashCode

class Operations {

Operation op1

Operation op2

static constraints = {

op1 bindable:true

op2 bindable:true

}

static embedded = ['op1', 'op2']

}

@EqualsAndHashCode

public class Operation {

String label

double number1

double number2

public Operation() {

super()

}

}

and my test:

@Test

void testMarshallJsonUsingConstructor() {

Operation op1 = new Operation(label: "test1", number1:95.1, number2:84.1 )

Operation op2 = new Operation(label: "test2", number1:85.1, number2:74.1 )

Operations r = new Operations(op1:op1,op2:op2)

assertEquals(op1, r.op1)

assertEquals(op2, r.op2)

Gson g = new GsonBuilder().disableInnerClassSerialization().create()

String json = g.toJson(r)    // this line blows the stack overflow

print json

}

[Jesse Wilson]

Could you paste the full stack trace? You've only pasted about 20 stack frames and the VM usually needs far more than that to trigger a stack overflow. I suspect you've got an unexpected circular reference, which should reveal itself in the way your stack frames repeat themselves.

[Brian Bonner]

Here's the full stack trace.  Sorry, I thought I cut it off where it was repeating.

java.lang.StackOverflowError

at java.io.StringWriter.write(StringWriter.java:84)

at java.io.StringWriter.append(StringWriter.java:126)

at java.io.StringWriter.append(StringWriter.java:24)

at com.google.gson.stream.JsonWriter.beforeValue(JsonWriter.java:610)

at com.google.gson.stream.JsonWriter.open(JsonWriter.java:317)

at com.google.gson.stream.JsonWriter.beginObject(JsonWriter.java:300)

at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:190)

at com.google.gson.internal.bind.ObjectTypeAdapter.write(ObjectTypeAdapter.java:105)

at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)

[Brian Bonner]

Was the full stack trace helpful at all?

[Brian Bonner]

I found some more information.   I debugged it and noticed that it started in the circular loop when it hit the errors property (a dynamically added property in grails).  This explains why it doesn't occur when I do it w/ Java and Groovy -- this property doesn't get added.

When it does this, it finds another class property called target and then it goes through the entire class again.

I'm not sure why errors and target does this, but I'm going to try to exclude errors and see if I get farther.

[Brian Bonner]

I included an Exclusion strategy to remove the errors field from serialization...I'm not sure if this is the best strategy, but it's working for now.

/**

 * This class is used because GSON seems to hate serializing the Grails errors

 * class and gets into an infinite loop. See:

 * https://groups.google.com/d/topic/google-gson/AX48GpVHjgQ/discussion

 * 

 * @author bbonner

 * 

 */

public class GrailsDomainExclusionStrategy implements ExclusionStrategy {

@Override

public boolean shouldSkipClass(Class<?> clazz) {

return false;

}

@Override

public boolean shouldSkipField(FieldAttributes f) {

if (f.getName().equals("errors")) {

return true;

}

return false;

}

}

I then created a GSON instance as explained in the User Guide:

Gson g = new GsonBuilder().setExclusionStrategies(new GrailsDomainExclusionStrategy()).create()

String json = g.toJson(r)

I'm not sure if this is necessary going to give me what I want, but it definitely removes the circular reference.

Here's the resulting JSON:

{"op1":{"label":"test1","number1":95.1,"number2":84.1},"op2":{"label":"test2","number1":85.1,"number2":74.1}}

If I alternatively remove the 'target' property instead of 'errors' in the strategy, I get JSON that looks like:  

{"op1":{"label":"test1","number1":95.1,"number2":84.1},"op2":{"label":"test2","number1":85.1,"number2":74.1},"errors":{"autoGrowNestedPaths":true,"autoGrowCollectionLimit":2147483647,"objectName":"gsongrailstest.Operations","messageCodesResolver":{"prefix":""},"errors":[],"suppressedFields":[],"nestedPath":"","nestedPathStack":[]}}

I've italicized the 'extra information that Grails seems to be including.