Hibernate general serialization scheme to avoid delay loading problem and serialization of entire database to client

The process of using ajax:hibernate Entity => json, Flex remoteobject:hibernate Entity => ActionScript object frequently encounters the following problems:

Problem:

1.Hibernate throws Lazyinitializationexception If session is closed when a deferred-load property access is encountered

In the case of One-to-many in 2.Hibernate, if there is no control in serialization, the entire database may be serialized

3. Excessive use of dto/valueobject to solve this problem.

Solution:

Generates a dynamic proxy for the entity object, blocks the Getxxxx () method, and if you are accessing a deferred-loading property, return null instead of throwing the lazyinitializationexception, recursively generating the code for the property, Serialization automatically stops whenever a property is encountered that does not delay loading. Avoid serializing the entire entity, causing problems that might serialize the entire database.

Similar solutions:

Hibernateconverter in Dwr, when serialized, a property that encounters a deferred load automatically stops the convert operation. and Hibernatebeanserializer is once and for all, regardless of object => JSON can work.

Use Use cases:

Java code

//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

Source.

Java code

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;





/**


* is used for serialization of Hibernate Object, the property that accesses the deferred load does not throw a lazyinitializationexception and returns a null value.


* Use:


* <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 is a lazy-collection so we need to double check


if (! Hibernate.isinitialized (returnvalue)) {


return null;


　　 }





//this is Hibernate Object


if (returnvalue instanceof hibernateproxy) {


return to New Hibernatebeanserializer (returnvalue). GetProxy ();


}else if (returnvalue instanceof persistentcollection) {


if (Returntype.isassignablefrom (Map.class)) {


Map proxymap = new Linkedhashmap ();


map map = (map) returnvalue;


set<map.entry> entryset = Map.entryset ();


for (Map.entry entry:entryset) {


Proxymap.put (Entry.getkey (), New Hibernatebeanserializer (Entry.getvalue ()));


　　　 }


return proxymap;


　　 }





Collection proxycollection = null;


if (Returntype.isassignablefrom (Set.class)) {


proxycollection = new Linkedhashset ();


}else if (Returntype.isassignablefrom (List.class)) {


proxycollection = new ArrayList ();


}else {


return returnvalue;


　　 }





for (Object o: (Collection) returnvalue) {


Proxycollection.add (new Hibernatebeanserializer (O). GetProxy ());


　　 }


return proxycollection;


}else {


return returnvalue;


　　 }


　 }





Private Boolean isexclude (methodinvocation mi, String PropertyName)


throws Throwable {





for (String excludepropertyname:excludesproperties) {


if (propertyname.equals (Excludepropertyname)) {


return true;


　　 }


　　 }





return false;


　 }





private static string Getpropertyname (String methodname) {


String propertyname = null;


if (Methodname.startswith ("get")) {


propertyname = methodname.substring ("Get". Length ());


}else if (Methodname.startswith ("is")) {


PropertyName = Methodname.substring ("is". Length ());


}else if (Methodname.startswith ("set")) {


propertyname = methodname.substring ("set". Length ());


　　 }


return propertyname = = null? Null:StringUtils.uncapitalize (PropertyName);


　 }


　 }


}

Another of these classes is part of the Rapid-framework, and the v2.0 version of Flex RemoteObject will use this approach. The preview version is about to be released