xstream

XStream with hibernate 解决Cannot handle CGLIB enhan

关键字: xstream

 

from:http://ericyou.iteye.com/blog/309763

 

在hibernate下使用XStream会有Cannot handle CGLIB enhanced proxies with multiple callbacks的问题，原因在于hibernate取出来的集合对象其实不是POJO的集合，而是依赖于HIBERNATE API的代理对象，在网上找了下，找到这篇文章
先做记录，有时间做下翻译

以下的代码只在hibernate 2下面做了测试，但是理论上同样适用于hibernate 3

解决这个问题的关键在于，让JVM像处理java.util包下面的 Collection一样处理hibernate的Collection，这样就可以避免臭名昭著"com.thoughtworks.xstream.converters.ConversionException: Cannot handle CGLIB enhanced proxies with multiple callbacks..."异常。

主要分为三个步骤，首先，告诉Xstream像处理java Collection一样处理hibernate Collection

xstream.addDefaultImplementation(
         net.sf.hibernate.collection.List.class, java.util.List.class);
xstream.addDefaultImplementation(
         net.sf.hibernate.collection.Map.class, java.util.Map.class);
xstream.addDefaultImplementation(
         net.sf.hibernate.collection.Set.class, java.util.Set.class);

xstream.addDefaultImplementation(
        net.sf.hibernate.collection.List.class, java.util.List.class);
xstream.addDefaultImplementation(
        net.sf.hibernate.collection.Map.class, java.util.Map.class);
xstream.addDefaultImplementation(
        net.sf.hibernate.collection.Set.class, java.util.Set.class);

然后需要注册一些Coverter来帮助Xstream处理这些hibernaye Collection

Mapper mapper = xstream.getMapper();
 xstream.registerConverter(new HibernateCollectionConverter(mapper));
 xstream.registerConverter(new HibernateMapConverter(mapper));

Mapper mapper = xstream.getMapper();
xstream.registerConverter(new HibernateCollectionConverter(mapper));
xstream.registerConverter(new HibernateMapConverter(mapper));

这样，这些转换器就加入到了Xstream内建的转换器队列当中。在完成了具体的转换代码之后，Xstream就具备了处理hibernate Collection的能力

import net.sf.hibernate.collection.List;
 import net.sf.hibernate.collection.Set;
 import com.thoughtworks.xstream.converters.collections.CollectionConverter;
 import com.thoughtworks.xstream.mapper.Mapper;

 class HibernateCollectionConverter extends CollectionConverter {
    HibernateCollectionConverter(Mapper mapper) {
         super(mapper);
    }

     public boolean canConvert(Class type) {
         return super.canConvert(type) || type == List.class || type == Set.class;
    }
}

import net.sf.hibernate.collection.List;
import net.sf.hibernate.collection.Set;
import com.thoughtworks.xstream.converters.collections.CollectionConverter;
import com.thoughtworks.xstream.mapper.Mapper;

class HibernateCollectionConverter extends CollectionConverter {
    HibernateCollectionConverter(Mapper mapper) {
        super(mapper);
    }

    public boolean canConvert(Class type) {
        return super.canConvert(type) || type == List.class || type == Set.class; 
    }
}

and

import net.sf.hibernate.collection.Map;
 import com.thoughtworks.xstream.converters.collections.MapConverter;
 import com.thoughtworks.xstream.mapper.Mapper;

 class HibernateMapConverter extends MapConverter {

    HibernateMapConverter(Mapper mapper) {
         super(mapper);
    }

     public boolean canConvert(Class type) {
         return super.canConvert(type) || type == Map.class;
    }
}

import net.sf.hibernate.collection.Map;
import com.thoughtworks.xstream.converters.collections.MapConverter;
import com.thoughtworks.xstream.mapper.Mapper;

class HibernateMapConverter extends MapConverter {

    HibernateMapConverter(Mapper mapper) {
        super(mapper);
    }

    public boolean canConvert(Class type) {
        return super.canConvert(type) || type == Map.class; 
    }
}

这些就可以解决Hibernate + Xstream出现的问题，Good Luck!