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:

?

//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.

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(){
		return this.proxy;
	}
	
	static private class HibernateBeanSerializerAdvice implements MethodInterceptor {
		private String[] excludesProperties = new String[0]; 
		public String[] getExcludesProperties() {
			return excludesProperties;
		}
		public void setExcludesProperties(String[] excludesProperties) {
			this.excludesProperties = excludesProperties == null ? new String[0] : excludesProperties;
		}
		public Object invoke(MethodInvocation mi) throws Throwable {
			String propertyName = getPropertyName(mi.getMethod().getName());
			Class returnType = mi.getMethod().getReturnType();
			
			if(propertyName == null) {
				return mi.proceed();
			}
			if(!Hibernate.isPropertyInitialized(mi.getThis(), propertyName)) {
				return null;
			}
			if(isExclude(mi, propertyName)) {
				return null;
			}
			
			Object returnValue = mi.proceed();
			return processReturnValue(returnType, returnValue);
		}
		
		private Object processReturnValue(Class returnType, Object returnValue) {
			if(returnValue == null)
				return null;
			if(returnType != null && Modifier.isFinal(returnType.getModifiers())) {
				return returnValue;
			}
			//This might be a lazy-collection so we need to double check
			if(!Hibernate.isInitializ