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 的代理,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 nullRole proxyRole = (Role) new HibernateBeanSerializer(role).getProxy ();assertNotNull(role.getResource());assertNull (proxyRole.getResource()); //延迟加载,为nullHibernate.initialize (role.getResource()); //抓取进来 assertNotNull (proxyRole.getResource()); //不为null//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 nullRole proxyRole = (Role)new HibernateBeanSerializer(role).getProxy ();assertNotNull(role.getResource());assertNull (proxyRole.getResource()); //延迟加载,为nullHibernate.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: *
<br />* Blog proxyBlog = new HibernateBeanSerializer(blog).getProxy();<br />*
* @author badqiu * @param */ public class HibernateBeanSerializer { 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.isInitialized(returnValue)) { return null ; } //this is Hibernate Object if (returnValue instanceof HibernateProxy) { return new HibernateBeanSerializer (returnValue).getProxy(); } else if (returnValue instanceof PersistentCollection) { if (returnType.isAssignableFrom(Map. class )) { Map proxyMap = new LinkedHashMap(); Map map = (Map)returnValue; Set
<br />* Blog proxyBlog = new HibernateBeanSerializer(blog).getProxy();<br />*
* @author badqiu* @param */public class HibernateBeanSerializer {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(Modifier.isFinal(returnType.getModifiers())) { return returnValue; } //This might be a lazy-collection so we need to double check if(!Hibernate.isInitialized(returnValue)) { return null; } //this is Hibernate Object if (returnValue instanceof HibernateProxy) { return new HibernateBeanSerializer(returnValue).getProxy(); }else if (returnValue instanceof PersistentCollection) { if (returnType.isAssignableFrom(Map.class)) { Map proxyMap = new LinkedHashMap(); Map map = (Map)returnValue; Set
另这个类属于rapid-framework的一部分,v2.0版本的flex RemoteObject将采 用这个办法.preview版本即将发布
接受失败等于回归真实的自我,接受失败等于打破完美的面具,