Hibernate通用序列化方案,避免延迟加载问题及序列化整个数据库至客户端
时间:2011-01-03 javaeye badqiu
在使用Ajax: Hibernate Entity => json, Flex RemoteObject: Hibernate Entity => ActionScript Object的过程,经常碰到如下问题:
问题:
1.Hibernate碰到延迟加载的属性访问时如果session被关闭则抛出LazyInitializationException
2.Hibernate中的one-to-many等关联关系在序列化时如果没有控制,则将整个数据库都有可能被全部序列化
3.过多的使用DTO/ValueObject解决这个问题.
解决办法:
对Entity对象生成一个动态代理,拦截getXXXX()方法,如果访问的是延迟加载的属性,则return null,而不抛出LazyInitializationException,递归生成属性的代码,只要碰到未延迟加载的属性,而序列化会自动停止.避免将整个Entity序列化传播,导致可能序列化整个数据库的问题.
类似解决方案:
dwr中HibernateConverter,在序列化时如上类似,碰到延迟加载的属性自动停止convert工作.而HibernateBeanSerializer则一劳永逸,无论object => json都可以工作.
使用用例:
Java代码
//role为原始对象
role = (Role)roleDao.getById(new Long(1));
//生成的动态代理proxyRole,访问延迟加载的属性将return null
Role proxyRole = (Role)new HibernateBeanSerializer<Role>(role).getProxy();
assertNotNull(role.getResource());
assertNull(proxyRole.getResource()); //延迟加载,为null
Hibernate.initialize(role.getResource()); //抓取进来
assertNotNull(proxyRole.getResource()); //不为null
源码.
Java代码
package cn.org.rapid_framework.util;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.hibernate.Hibernate;
import org.hibernate.collection.PersistentCollection;
import org.hibernate.proxy.HibernateProxy;
import org.springframework.aop.framework.ProxyFactory;
import org.springframework.util.StringUtils;
/**
* 用于Hibernate Object 的序列化,访问延迟加载的属性不会抛出LazyInitializationException,而会返回null值.
* 使用:
* <pre>
* Blog proxyBlog = new HibernateBeanSerializer(blog).getProxy();
* </pre>
* @author badqiu
* @param <T>
*/
public class HibernateBeanSerializer <T> {
T proxy = null;
/**
*/
public HibernateBeanSerializer(T object,String... excludesProperties) {
if(object == null) {
this.proxy = null;
}else {
ProxyFactory pf = new ProxyFactory();
pf.setTargetClass(object.getClass());
pf.setOptimize(true);
pf.setTarget(object);
pf.setProxyTargetClass(true);
pf.setOpaque(true);
pf.setExposeProxy(true);
pf.setPreFiltered(true);
HibernateBeanSerializerAdvice beanSerializerAdvice = new HibernateBeanSerializerAdvice();
beanSerializerAdvice.setExcludesProperties(excludesProperties);
pf.addAdvice(beanSerializerAdvice);
this.proxy = (T)pf.getProxy();
}
}
public T getProxy
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