Jersey JAX-RS，Hibernate和LazyInitializationException [英] Jersey JAX-RS, Hibernate and LazyInitializationException

问题描述

我正在研究Java EE 6.0 RESTful应用程序，并使用Hibernate。我需要在序列化之前取消代理我的惰性加载对象（实际上是实体的惰性加载的实体属性）以避免LazyInitializationException。我已经在AMF服务中成功完成了这一任务，编写了一些实用程序，在序列化实体之前做了这些工作。

我正在使用Jersey JAX-RS实现，我需要做这与杰克逊。我在BeanSerializer中发现了一个地方，我相信代理可以发生并且工作正常，但是我需要以这种方式更改一个库类，而且我不想。

所以这里是我更改后的BeanSerializer.serialize方法：

  @Override 
 public final void serialize（Object bean，JsonGenerator jgen，SerializerProvider提供者）
抛出IOException，JsonGenerationException 
 {
 bean = Util.deproxy（bean）; // *****在这里deproxy这个bean ***** 
 
 jgen.writeStartObject（）; 
 
 if（_propertyFilterId！= null）{
 serializeFieldsFiltered（bean，jgen，provider）; 
} else {
 serializeFields（bean，jgen，provider）; 
} 
 
 jgen.writeEndObject（）; 
 
  

我的问题是如何在不更改库类的情况下执行此操作BeanSerializer）？如果有正确的方法，我不喜欢这种黑客攻击。

解决方案

我试图特别用集合来做到这一点。因此，我为hibernate的 PersistenceBag 添加了新的序列化程序到我的 ObjectMapper 中：

  simpleModule.addSerializer（PersistentBag.class，new JsonSerializer< PersistentBag>（）{
 @Override $ b $ public void serialize（final PersistentBag集合，final JsonGenerator jsonGenerator，final SerializerProvider serializerProvider）throws IOException {
 if（collection.wasInitialized（））{
 final Iterator iterator = collection.iterator（）; 
 //这样做是为了防止无限递归，因为如果我们编写PersistenceBag，它会被再次序列化。 b $ b jsonGenerator.writeObject（Iterators.toArray（iterator，Object.class））; 
} else {
 //这样做是为了防止NPE和未定义的引用（集合应该是空的，但不能null）
 jsonGenerator.writeStartArray（）; 
 jsonGenerator.writeEndArray（）; 
} 
} 
}）; 
 objectMapper.registerModule（simpleModule）; 
  

这可以防止 LazyInitializationException 。如果集合未初始化，则它被写为空数组，否则它就是序列化的。

（迭代器来自Google Guava lib）

I am working on a Java EE 6.0 RESTful app and I am using Hibernate. I need to de-proxy my lazy loaded objects(actually the lazy loaded entity properties of an entity) before serialization to avoid the LazyInitializationException. I have done this with AMF services successfully by coding some utility that does just that before serializing the entity.

I am using the Jersey JAX-RS implementation and I need to do this with Jackson. I have found a spot in the BeanSerializer where I believed the de-proxying could take place and it works fine but I will need to change a library class in this way and I don't want to.

So here is the BeanSerializer.serialize method after my change:

@Override
public final void serialize(Object bean, JsonGenerator jgen, SerializerProvider provider)
throws IOException, JsonGenerationException
{
  bean =  Util.deproxy(bean); // ***** Deproxy the bean here *****

  jgen.writeStartObject();

  if (_propertyFilterId != null) {
    serializeFieldsFiltered(bean, jgen, provider);
  } else {
    serializeFields(bean, jgen, provider);
  }

  jgen.writeEndObject();
}

My question is how to do this without changing a library class(BeanSerializer)? I don't like this kind of hacks if there is a proper way.

解决方案

I've tried to do this particularly with Collections. So I've added new serializer for hibernate's PersistenceBag into mine ObjectMapper:

simpleModule.addSerializer(PersistentBag.class, new JsonSerializer<PersistentBag>() {
  @Override
  public void serialize(final PersistentBag collection, final JsonGenerator jsonGenerator, final SerializerProvider serializerProvider) throws IOException {
     if(collection.wasInitialized()){
        final Iterator iterator = collection.iterator();
        //this is done to prevent Infinite Recursion, cause if we write PersistenceBag it will be serialized again.         
        jsonGenerator.writeObject(Iterators.toArray(iterator,Object.class));
     }else{
        //this is done to prevent NPE and undefined reference. (collections should be empty, but not null)
        jsonGenerator.writeStartArray();
        jsonGenerator.writeEndArray();
     }
  }
});
objectMapper.registerModule(simpleModule);

This prevents LazyInitializationException. If collections is not initialized it is written as empty array, otherwise it is just serialized.

(Iterators is from Google Guava lib)

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