Marcono1234
commented
1 year ago Have added the "enhancement" label because there was never really proper support for Throwable; it just accessed the internal fields of the JDK classes. And that was already flawed; if Throwable.getStackTrace() had not been called (indirectly) before the exception was passed to Gson, the JSON output would contain "stackTrace":[] because the stack trace had not been initialized yet. It also did not include the exception type, so if the exception message itself was not meaningful enough (e.g. NullPointerException might not have any message at all), you would have no clue what kind of exception occurred.
Backward compatibility might also be a (small) problem: If Gson added now a type adapter factory which handles Throwable and all subclasses, it would not include custom fields from subclasses anymore.
Most likely it is also not possible to properly support deserialization because exceptions can have arbitrary constructors (which might make adjustments to the provided message), so even if Gson was able to create an instance of an exception, the instance would most likely not be identical to the original one.
Note that I am not a direct member of this project, but my opinion is that users should write their own adapter, and include all information they consider important. Here is an example for including the type name, the message, the cause and suppressed exceptions:
class ThrowableAdapterFactory implements TypeAdapterFactory {
private ThrowableAdapterFactory() {}
public static final ThrowableAdapterFactory INSTANCE = new ThrowableAdapterFactory();
@Override
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
// Only handles Throwable and subclasses; let other factories handle any other type
if (!Throwable.class.isAssignableFrom(type.getRawType())) {
return null;
}
@SuppressWarnings("unchecked")
TypeAdapter<T> adapter = (TypeAdapter<T>) new TypeAdapter<Throwable>() {
@Override
public Throwable read(JsonReader in) throws IOException {
throw new UnsupportedOperationException();
}
@Override
public void write(JsonWriter out, Throwable value) throws IOException {
if (value == null) {
out.nullValue();
return;
}
out.beginObject();
// Include exception type name to give more context; for example NullPointerException might
// not have a message
out.name("type");
out.value(value.getClass().getSimpleName());
out.name("message");
out.value(value.getMessage());
Throwable cause = value.getCause();
if (cause != null) {
out.name("cause");
write(out, cause);
}
Throwable[] suppressedArray = value.getSuppressed();
if (suppressedArray.length > 0) {
out.name("suppressed");
out.beginArray();
for (Throwable suppressed : suppressedArray) {
write(out, suppressed);
}
out.endArray();
}
out.endObject();
}
};
return adapter;
}
}And then register it like this:
new GsonBuilder()
.registerTypeAdapterFactory(ThrowableAdapterFactory.INSTANCE)
.create()Edit: You could probably also simplify this to only write a TypeAdapter with the above code instead of a TypeAdapterFactory and then register it with GsonBuilder.registerTypeHierarchyAdapter instead.
q3769
Gson version
2.10.1
Java / Android version
17.0.6 Amazon Corretto
Used tools
Description
Expected behavior
Gson should serialize the ExBean instance with the Throwable field, with stack trace details and related info on the Exception.
Actual behavior
Gson.toJson errors out with exception. See stack trace below.
Reproduction steps
Exception stack trace