Get HibernateProxy at one object

Question

I work at a spring boot API. It's the first time I get this problem.

I'm loading different company objects via the findById function with the repository. All company objects are loaded correctly, expect one. This one loads a handler property of type JavassistLazyInitalizer with it. The remaining properties are all on the default value. In the handler object in the target node is the object loaded correctly how I want it.

So I found out that this is a type of hibernate lazy loading, because when I want to access a property with a getter, it works correctly.

My problem is, that I want to serialize the object with gson at the end and I get this error during serilazition process:

Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter?

I understand why this error occurs. But I don't understand why only one of the different company objects is loaded lazy(or is a hibernateProxy). So what is the smartest way to avoid the hibernateProxy, respectively to serialize the object?

Thanks for your answers :)

It's not the best idea to serialize entities. Especially if they have relationships between eachother - you can get into a recursion trap — Veselin Davidov, Nov 14 '18 at 10:55
They haven't relationships between eachother, but thanks for your hint :) — Amannti, Nov 14 '18 at 10:57

score 0 · Answer 1 · answered Nov 14 '18 at 12:40

The reason can be that you do some operations with correctly loaded objects. For example, if you call any method (not necessary getter) of a loaded persistent class, Hibernate initializes all proxies.

And you do nothing with an object that is loaded incorrectly.

score 0 · Accepted Answer · answered Nov 14 '18 at 13:51

This Adapter is my solution.

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);
}

}

You have to add this to your gsonBuilder.

new GsonBuilder().registerTypeAdapterFactory(HibernateProxyTypeAdapter.FACTORY).create();

Answer found on this question Could not serialize object cause of HibernateProxy

Get HibernateProxy at one object

2 Answers2