使用Gson转换Hibernate对象遇到一个问题，当对象的Lazy加载的，就会出现上面的错误。处理方式摘抄自网上，留存一份以后自己看。

/*** 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;}@Overridepublic HibernateProxy read(JsonReader in) throws IOException {throw new UnsupportedOperationException("Not supported");}@SuppressWarnings({"rawtypes", "unchecked"})@Overridepublic void write(JsonWriter out, HibernateProxy value) throws IOException {if (value == null) {out.nullValue();return;}// Retrieve the original (not proxy) classClass<?> baseType = Hibernate.getClass(value);// Get the TypeAdapter of the original class, to delegate the serializationTypeAdapter delegate = context.getAdapter(TypeToken.get(baseType));// Get a filled instance of the original classObject unproxiedValue = ((HibernateProxy) value).getHibernateLazyInitializer().getImplementation();// Serialize the valuedelegate.write(out, unproxiedValue);}
}

实现上面的类，然后就是使用：

GsonBuilder b = new GsonBuilder();
...
b.registerTypeAdapterFactory(HibernateProxyTypeAdapter.FACTORY);
...
Gson gson = b.create();

解释，只是看不懂。

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.