NPE while invoke toJson() or fromJson() for HashMap<String, String> #1778

zewenwang · 2020-09-11T08:27:27Z

the exception:

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Object.hashCode()' on a null object reference
  libcore.reflect.TypeVariableImpl.hashCode(TypeVariableImpl.java:47)
  java.util.HashMap.hash(HashMap.java:338)
  java.util.HashMap.containsKey(HashMap.java:595)
  java.util.HashSet.contains(HashSet.java:203)
  com.google.gson.internal.$Gson$Types.resolve(.java:346)
  com.google.gson.internal.$Gson$Types.resolve(.java:381)
  com.google.gson.internal.$Gson$Types.resolve(.java:337)
  com.google.gson.internal.$Gson$Types.getSupertype(.java:283)
  com.google.gson.internal.$Gson$Types.getCollectionElementType(.java:302)
  com.google.gson.internal.bind.CollectionTypeAdapterFactory.create(CollectionTypeAdapterFactory.java:52)
  com.google.gson.Gson.getAdapter(Gson.java:458)
  com.google.gson.Gson.toJson(Gson.java:696)
  com.google.gson.Gson.toJson(Gson.java:683)
  com.google.gson.Gson.toJson(Gson.java:638)
  com.google.gson.Gson.toJson(Gson.java:618)

my code:

new Gson().fromJson(json, new TypeToken<HashMap<String, String>>() {}.getType());

environment

Gson version 2.8.5
The probability of this problem happens substantial increases，when gson version upgrades from 2.8.2 to 2.8.5 !

Same problem with #1298 , but not resolved.

The text was updated successfully, but these errors were encountered:

zewenwang · 2020-09-11T08:32:15Z

@JakeWharton @Marcono1234 @inder123 @Degubi

Marcono1234 · 2020-09-11T19:07:00Z

Could this possibly be an Android bug (libcore.reflect.TypeVariableImpl is an Android class)? I assume Gson is not creating the TypeVariableImpl on its own but probably retrieves it somehow from a parameterized type, in that case Android would be the one creating that TypeVariableImpl which is causing the issues.

Could you please debug into TypeVariableImpl and check which expression is causing the NullPointerException?

fvdcx · 2020-09-25T03:02:20Z

I also met this issue, but my code calls "toJson" on a HashMap<String, Object>. @Marcono1234 @zewenwang
how to escalate this bug?

Marcono1234 · 2020-09-25T20:29:39Z

As written in my comment above it would probably first be useful to get more information about which variable is null.

Aquarids · 2020-11-02T03:30:59Z

I also met this issue, but my code calls "toJson" on a HashMap<String, Object>. @Marcono1234 @zewenwang
how to escalate this bug?

metoo, is there a fixed method?

Marcono1234 · 2020-11-02T15:18:46Z

As written above, it would be useful if you could provide more information:

Could this possibly be an Android bug (libcore.reflect.TypeVariableImpl is an Android class)? I assume Gson is not creating the TypeVariableImpl on its own but probably retrieves it somehow from a parameterized type, in that case Android would be the one creating that TypeVariableImpl which is causing the issues.

Could you please debug into TypeVariableImpl and check which expression is causing the NullPointerException?

Aquarids · 2020-11-03T01:48:29Z

As written above, it would be useful if you could provide more information:

Could this possibly be an Android bug (libcore.reflect.TypeVariableImpl is an Android class)? I assume Gson is not creating the TypeVariableImpl on its own but probably retrieves it somehow from a parameterized type, in that case Android would be the one creating that TypeVariableImpl which is causing the issues.
Could you please debug into TypeVariableImpl and check which expression is causing the NullPointerException?

Sorry, here is the stacktrace.

libcore.reflect.TypeVariableImpl.hashCode(TypeVariableImpl.java:47)
java.util.HashMap.hash(HashMap.java:348)
java.util.HashMap.containsKey(HashMap.java:608)
java.util.HashSet.contains(HashSet.java:203)
com.google.gson.internal.$Gson$Types.resolve(.java:346)
com.google.gson.internal.$Gson$Types.resolve(.java:381)
com.google.gson.internal.$Gson$Types.resolve(.java:337)
com.google.gson.internal.$Gson$Types.getSupertype(.java:283)
com.google.gson.internal.$Gson$Types.getCollectionElementType(.java:302)
com.google.gson.internal.bind.CollectionTypeAdapterFactory.create(CollectionTypeAdapterFactory.java:52)
com.google.gson.Gson.getAdapter(Gson.java:458)
com.google.gson.Gson.toJson(Gson.java:696)
com.google.gson.Gson.toJson(Gson.java:683)
com.google.gson.Gson.toJson(Gson.java:638)

And my code is:

List<MyCustomClass> list = new ArrayList<>();
mGson.toJson(list);

or

List<MyCustomClass> list = new ArrayList<>();
mGson.toJson(list, TypeToken.getParameterized(List.class, MyCustomClass.class).getType());

Cyux07 · 2020-11-03T02:26:17Z

it looks like a NULL generic declaration of class cause NPE.
https://android.googlesource.com/platform/libcore/+/master/luni/src/main/java/libcore/reflect/TypeVariableImpl.java

@Override
    public int hashCode() {
        return 31 * getName().hashCode() + getGenericDeclaration().hashCode();
    }

follow the trace, the toResolve's generic type lost?:

 private static Type resolve(Type context, Class<?> contextRawType, Type toResolve,
                              Collection<TypeVariable> visitedTypeVariables) {
    // this implementation is made a little more complicated in an attempt to avoid object-creation
    while (true) {
      if (toResolve instanceof TypeVariable) {
        TypeVariable<?> typeVariable = (TypeVariable<?>) toResolve;
        if (visitedTypeVariables.contains(typeVariable)) {
          // cannot reduce due to infinite recursion
          return toResolve;
        } else {
          visitedTypeVariables.add(typeVariable);
        }
        toResolve = resolveTypeVariable(context, contextRawType, typeVariable);
        if (toResolve == typeVariable) {
          return toResolve;
        }

      }......

And the toResolve come from $Gson$Types.getGenericSupertype(context, contextRawType, supertype).

Maybe this method return a NULL generic type collection in some case?

static Type getSupertype(Type context, Class<?> contextRawType, Class<?> supertype) {
    if (context instanceof WildcardType) {
      // wildcards are useless for resolving supertypes. As the upper bound has the same raw type, use it instead
      context = ((WildcardType)context).getUpperBounds()[0];
    }
    checkArgument(supertype.isAssignableFrom(contextRawType));
    return resolve(context, contextRawType,
        $Gson$Types.getGenericSupertype(context, contextRawType, supertype));
  }

Marcono1234 · 2020-11-15T16:52:31Z

Are you able to reproduce this exception when debugging on an emulator, or only for the deployed app? Which Android API Level does the target device have? Are you using a custom ProGuard configuration?

If possible could you please create a small example project which only contains the relevant code, which allows reproducing this issue (and describe reproduction steps if necessary).

Aquarids · 2020-11-19T01:48:12Z

Are you able to reproduce this exception when debugging on an emulator, or only for the deployed app? Which Android API Level does the target device have? Are you using a custom ProGuard configuration?

If possible could you please create a small example project which only contains the relevant code, which allows reproducing this issue (and describe reproduction steps if necessary).

Thanks for your reply, we have solved this problem by wrapping a JsonObject on the JsonArray. And this is an online occasional problem which reproted by our user, thus we also don't have more information to identify the reason of the problem.

EmMper · 2020-12-30T07:42:18Z

It happened to me on version 2.8.2, the same stack trace, and I also wrote the code below:

// Kotlin Code
Gson().fromJson(jsonString, object : TypeToken<List<MyCustomClass>>() {})

to deserialize with a type token, I think this may be a clue.
And this problem won't happened every time, actually the frequency of problems is pretty low. So I'm not sure how to reproducing it.
Now I'm trying to update Gson to the newest version 2.8.6, and I wonder will this issue happen again.

EmMper · 2020-12-30T07:50:16Z

Are you able to reproduce this exception when debugging on an emulator, or only for the deployed app? Which Android API Level does the target device have? Are you using a custom ProGuard configuration?
If possible could you please create a small example project which only contains the relevant code, which allows reproducing this issue (and describe reproduction steps if necessary).

Thanks for your reply, we have solved this problem by wrapping a JsonObject on the JsonArray. And this is an online occasional problem which reproted by our user, thus we also don't have more information to identify the reason of the problem.

So your resolvent is to use another serialization tool? I noticed that you are in Beijing too, may I get your wechat or something to communicate with you?

Aquarids · 2021-01-04T01:46:18Z

Are you able to reproduce this exception when debugging on an emulator, or only for the deployed app? Which Android API Level does the target device have? Are you using a custom ProGuard configuration?
If possible could you please create a small example project which only contains the relevant code, which allows reproducing this issue (and describe reproduction steps if necessary).

Thanks for your reply, we have solved this problem by wrapping a JsonObject on the JsonArray. And this is an online occasional problem which reproted by our user, thus we also don't have more information to identify the reason of the problem.

So your resolvent is to use another serialization tool? I noticed that you are in Beijing too, may I get your wechat or something to communicate with you?

没，我就直接用jsonObject又包了层，原本是[{"xxx", "yyy"}]，现在是 {"data": [{"xxx", "yyy"}]}就暂时解决了。原因就和上面Cyux07说的一样。

EmMper · 2021-01-08T07:58:39Z

Are you able to reproduce this exception when debugging on an emulator, or only for the deployed app? Which Android API Level does the target device have? Are you using a custom ProGuard configuration?
If possible could you please create a small example project which only contains the relevant code, which allows reproducing this issue (and describe reproduction steps if necessary).

Thanks for your reply, we have solved this problem by wrapping a JsonObject on the JsonArray. And this is an online occasional problem which reproted by our user, thus we also don't have more information to identify the reason of the problem.

So your resolvent is to use another serialization tool? I noticed that you are in Beijing too, may I get your wechat or something to communicate with you?

没，我就直接用jsonObject又包了层，原本是[{"xxx", "yyy"}]，现在是 {"data": [{"xxx", "yyy"}]}就暂时解决了。原因就和上面Cyux07说的一样。

OK，了解了。但依然可以认为是Gson自己的bug吧？总感觉这样处理不能算是最终方案

Marcono1234 · 2022-02-03T18:35:33Z

In this pull request Gson users tried to solve this by modifying their ProGuard rules.
Could you please try, with the latest version of Gson, whether disabling any shrinking and obfuscation for class com.google.gson.reflect.TypeToken and class * extends com.google.gson.reflect.TypeToken solves this issue?

Or in general make sure you apply the ProGuard rules shown in proguard.cfg, except for the one for com.google.gson.examples.android.model.**.

emanoellucasml · 2022-08-29T13:41:26Z

Hello, does anyone know if doing what @Marcono1234 suggested here the problem is solved? I am going through the same problem but updating the library version would affect many people, so I wanted to be sure before doing it.

Marcono1234 · 2022-08-29T14:24:43Z

I just mentioned using the latest Gson version to avoid having to debug issues in older versions, which might already be fixed in the latest version. Though this appears to be caused by ProGuard (or R8) so I assume adjusting the ProGuard rules without upgrading Gson might work as well.

vagrant1991 · 2023-09-15T11:51:20Z

https://issuetracker.google.com/issues/220725541

vagrant1991 · 2023-09-16T06:03:32Z

visit the above link, It sames like you have List, Map or Set (ex: ArrayList, HashSet) member in your java bean class, and not all of them using the @SerializedName annotation, so In R8 3.x, generics get stripped out, refer to : https://android.googlesource.com/platform/libcore/+/refs/heads/main/luni/src/main/java/libcore/reflect/TypeVariableImpl.java
when you call hashcode method, getGenericDeclaration return null, so you get NullPointerException,

com.google.gson.internal.$Gson$Types.getCollectionElementType(.java:302)

take a look at getCollectionElementType in $Gson$Types, As the method name show you, It's all about Collections.

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Marcono1234 mentioned this issue Feb 3, 2022

Occasional NullPointerException when calling Gson.fromJson when converting to a TypedToken of type CopyOnWriteArraySet #2070

Closed

Marcono1234 added bug needs-info labels Aug 12, 2022

Marcono1234 mentioned this issue Nov 1, 2022

NullPointerException during parsing object #1298

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Marcono1234 added the proguard-r8 Issues relating to the use of ProGuard and/or R8, such as problems due to obfuscation label Mar 29, 2024

eamonnmcmanus added the android Issues which are exclusive to Android, and don't occur with a JDK (even if ProGuard / R8 is used) label Jul 22, 2024

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NPE while invoke toJson() or fromJson() for HashMap<String, String> #1778

NPE while invoke toJson() or fromJson() for HashMap<String, String> #1778

zewenwang commented Sep 11, 2020

zewenwang commented Sep 11, 2020

Marcono1234 commented Sep 11, 2020

fvdcx commented Sep 25, 2020

Marcono1234 commented Sep 25, 2020

Aquarids commented Nov 2, 2020

Marcono1234 commented Nov 2, 2020

Aquarids commented Nov 3, 2020 •

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Cyux07 commented Nov 3, 2020

Marcono1234 commented Nov 15, 2020

Aquarids commented Nov 19, 2020

EmMper commented Dec 30, 2020 •

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EmMper commented Dec 30, 2020

Aquarids commented Jan 4, 2021

EmMper commented Jan 8, 2021

Marcono1234 commented Feb 3, 2022 •

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emanoellucasml commented Aug 29, 2022

Marcono1234 commented Aug 29, 2022 •

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vagrant1991 commented Sep 15, 2023

vagrant1991 commented Sep 16, 2023 •

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NPE while invoke toJson() or fromJson() for HashMap<String, String> #1778

NPE while invoke toJson() or fromJson() for HashMap<String, String> #1778

Comments

zewenwang commented Sep 11, 2020

the exception:

my code:

environment

zewenwang commented Sep 11, 2020

Marcono1234 commented Sep 11, 2020

fvdcx commented Sep 25, 2020

Marcono1234 commented Sep 25, 2020

Aquarids commented Nov 2, 2020

Marcono1234 commented Nov 2, 2020

Aquarids commented Nov 3, 2020 • edited Loading

Cyux07 commented Nov 3, 2020

Marcono1234 commented Nov 15, 2020

Aquarids commented Nov 19, 2020

EmMper commented Dec 30, 2020 • edited Loading

EmMper commented Dec 30, 2020

Aquarids commented Jan 4, 2021

EmMper commented Jan 8, 2021

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vagrant1991 commented Sep 15, 2023

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vagrant1991 commented Sep 16, 2023 •

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