You can do without manually unproxying everything by using a custom TypeAdapter.
Something along these lines:
/**
* This TypeAdapter unproxies Hibernate proxied objects, and serializes them
* through the registered (or default) TypeAdapter of the base class.
*/
public class HibernateProxyTypeAdapter extends TypeAdapter<HibernateProxy> {
public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
@Override
@SuppressWarnings("unchecked")
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
return (HibernateProxy.class.isAssignableFrom(type.getRawType()) ? (TypeAdapter<T>) new HibernateProxyTypeAdapter(gson) : null);
}
};
private final Gson context;
private HibernateProxyTypeAdapter(Gson context) {
this.context = context;
}
@Override
public HibernateProxy read(JsonReader in) throws IOException {
throw new UnsupportedOperationException("Not supported");
}
@SuppressWarnings({"rawtypes", "unchecked"})
@Override
public void write(JsonWriter out, HibernateProxy value) throws IOException {
if (value == null) {
out.nullValue();
return;
}
// Retrieve the original (not proxy) class
Class<?> baseType = Hibernate.getClass(value);
// Get the TypeAdapter of the original class, to delegate the serialization
TypeAdapter delegate = context.getAdapter(TypeToken.get(baseType));
// Get a filled instance of the original class
Object unproxiedValue = ((HibernateProxy) value).getHibernateLazyInitializer()
.getImplementation();
// Serialize the value
delegate.write(out, unproxiedValue);
}
}
To use it you must first register it:
GsonBuilder b = new GsonBuilder();
...
b.registerTypeAdapterFactory(HibernateProxyTypeAdapter.FACTORY);
...
Gson gson = b.create();
Notice that this will recursively initialize every proxy you have in the object hierarchy; since however you have to serialize the whole data, you should have done that anyway.
How does this work?
GSON contains a number of TypeAdapterFactory implementations, for various types (primitive types, common types like String or Date, lists, arrays...). Each factory is asked if it is able to serialize a certain Java type (the parameter to create is a TypeToken instead of a Class in order to capture possible information about generic types, which Class does not have). If the factory is able to serialize/deserialize a type, it responds with a TypeAdapter instance; otherwise it responds with null.
HibernateProxyTypeAdapter.FACTORY verifies whether type implements HibernateProxy; in that case, it returns an instance of HibernateProxyTypeAdapter for serialization.
The write method is called when an actual object has to be serialized; the adapter extracts the original type of the underlying object, and asks GSON for the standard TypeAdapter for the original type, which generally is a ReflectiveTypeAdapter.
Then it retrieves an instance of the original class, instead of directly using the proxy. This is necessary because ReflectiveTypeAdapter accesses directly to fields, instead of using getters; accessing to the fields of a proxied object does not work, and is a classical Hibernate pitfall.
As a possible performance improvement, the delegate TypeAdapter should be acquired in the create method. I found out that calling getSuperclass() on the proxy Class appears to yield the original base class. The code can then become:
public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
@Override
@SuppressWarnings("unchecked")
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
return (HibernateProxy.class.isAssignableFrom(type.getRawType())
? (TypeAdapter<T>) new HibernateProxyTypeAdapter((TypeAdapter)gson.getAdapter(TypeToken.get(type.getRawType().getSuperclass())))
: null);
}
};
private final TypeAdapter<Object> delegate;
private HibernateProxyTypeAdapter(TypeAdapter<Object> delegate) {
this.delegate = delegate;
}
@SuppressWarnings({"rawtypes", "unchecked"})
@Override
public void write(JsonWriter out, HibernateProxy value) throws IOException {
if (value == null) {
out.nullValue();
return;
}
delegate.write(out, ((HibernateProxy) value).getHibernateLazyInitializer()
.getImplementation());
}
