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

1. //role为原始对象   
2. role = (Role)roleDao.getById( new  Long( 1 ));   
3. //生成的动态代理proxyRole,访问延迟加载的属性将return null   
4. Role proxyRole = (Role) new  HibernateBeanSerializer<Role>(role).getProxy();   
5. assertNotNull(role.getResource());     
6. assertNull(proxyRole.getResource());  //延迟加载,为null   
7.   
8. Hibernate.initialize(role.getResource());  //抓取进来   
9. 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 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

1. package  cn.org.rapid_framework.util;   
2.   
3. import  java.lang.reflect.Modifier;   
4. import  java.util.ArrayList;   
5. import  java.util.Collection;   
6. import  java.util.LinkedHashMap;   
7. import  java.util.LinkedHashSet;   
8. import  java.util.List;   
9. import  java.util.Map;   
10. import  java.util.Set;   
11.   
12. import  org.aopalliance.intercept.MethodInterceptor;   
13. import  org.aopalliance.intercept.MethodInvocation;   
14. import  org.hibernate.Hibernate;   
15. import  org.hibernate.collection.PersistentCollection;   
16. import  org.hibernate.proxy.HibernateProxy;   
17. import  org.springframework.aop.framework.ProxyFactory;   
18. import  org.springframework.util.StringUtils;   
19.   
20. /**  
21.  * 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.  
22.  * 使用:  
23.  * <pre>  
24.  * Blog proxyBlog = new HibernateBeanSerializer(blog).getProxy();  
25.  * </pre>  
26.  * @author badqiu  
27.  * @param <T>  
28.  */   
29. public   class  HibernateBeanSerializer <T> {   
30.     T proxy =  null ;   
31.      /**  
32.      */   
33.      public  HibernateBeanSerializer(T object,String... excludesProperties) {   
34.          if (object ==  null ) {   
35.              this .proxy =  null ;   
36.         } else  {   
37.             ProxyFactory pf =  new  ProxyFactory();   
38.             pf.setTargetClass(object.getClass());   
39.             pf.setOptimize( true );   
40.             pf.setTarget(object);   
41.             pf.setProxyTargetClass( true );   
42.             pf.setOpaque( true );   
43.             pf.setExposeProxy( true );   
44.             pf.setPreFiltered( true );   
45.             HibernateBeanSerializerAdvice beanSerializerAdvice =  new  HibernateBeanSerializerAdvice();   
46.             beanSerializerAdvice.setExcludesProperties(excludesProperties);   
47.             pf.addAdvice(beanSerializerAdvice);   
48.                
49.              this .proxy = (T)pf.getProxy();   
50.         }   
51.     }   
52.   
53.      public  T getProxy(){   
54.          return   this .proxy;   
55.     }   
56.        
57.      static   private   class  HibernateBeanSerializerAdvice  implements  MethodInterceptor {   
58.          private  String[] excludesProperties =  new  String[ 0 ];    
59.          public  String[] getExcludesProperties() {   
60.              return  excludesProperties;   
61.         }   
62.          public   void  setExcludesProperties(String[] excludesProperties) {   
63.              this .excludesProperties = excludesProperties ==  null  ?  new  String[ 0 ] : excludesProperties;   
64.         }   
65.          public  Object invoke(MethodInvocation mi)  throws  Throwable {   
66.             String propertyName = getPropertyName(mi.getMethod().getName());   
67.             Class returnType = mi.getMethod().getReturnType();   
68.                
69.              if (propertyName ==  null ) {   
70.                  return  mi.proceed();   
71.             }   
72.              if (!Hibernate.isPropertyInitialized(mi.getThis(), propertyName)) {   
73.                  return   null ;   
74.             }   
75.              if (isExclude(mi, propertyName)) {   
76.                  return   null ;   
77.             }   
78.                
79.             Object returnValue = mi.proceed();   
80.              return  processReturnValue(returnType, returnValue);   
81.         }   
82.            
83.          private  Object processReturnValue(Class returnType, Object returnValue) {   
84.              if (returnValue ==  null )   
85.                  return   null ;   
86.              if (returnType !=  null  && Modifier.isFinal(returnType.getModifiers())) {   
87.                  return  returnValue;   
88.             }   
89.              //This might be a lazy-collection so we need to double check   
90.              if (!Hibernate.isInitialized(returnValue)) {   
91.                  return   null ;                   
92.             }   
93.                
94.              //this is Hibernate Object   
95.              if (returnValue  instanceof  HibernateProxy) {   
96.                  return   new  HibernateBeanSerializer(returnValue).getProxy();   
97.             } else   if (returnValue  instanceof  PersistentCollection) {   
98.                  if (returnType.isAssignableFrom(Map. class )) {   
99.                     Map proxyMap =  new  LinkedHashMap();   
100.                     Map map = (Map)returnValue;   
101.                     Set<Map.Entry> entrySet = map.entrySet();   
102.                      for (Map.Entry entry : entrySet) {   
103.                         proxyMap.put(entry.getKey(),  new  HibernateBeanSerializer(entry.getValue()));   
104.                     }   
105.                      return  proxyMap;   
106.                 }   
107.                    
108.                 Collection proxyCollection =  null ;   
109.                  if (returnType.isAssignableFrom(Set. class )) {   
110.                     proxyCollection =  new  LinkedHashSet();   
111.                 } else   if (returnType.isAssignableFrom(List. class )) {   
112.                     proxyCollection =  new  ArrayList();   
113.                 } else  {   
114.                      return  returnValue;   
115.                 }   
116.                    
117.                  for (Object o : (Collection)returnValue) {   
118.                     proxyCollection.add( new  HibernateBeanSerializer(o).getProxy());   
119.                 }   
120.                  return  proxyCollection;   
121.             } else  {   
122.                  return  returnValue;   
123.             }   
124.         }   
125.     
126.          private   boolean  isExclude(MethodInvocation mi, String propertyName)   
127.                  throws  Throwable {   
128.                
129.              for (String excludePropertyName : excludesProperties) {   
130.                  if (propertyName.equals(excludePropertyName)) {   
131.                      return   true ;   
132.                 }   
133.             }   
134.                
135.              return   false ;   
136.         }   
137.            
138.          private   static  String getPropertyName(String methodName) {   
139.             String propertyName =  null ;   
140.              if (methodName.startsWith( "get" )) {   
141.                 propertyName = methodName.substring( "get" .length());   
142.             } else   if (methodName.startsWith( "is" )) {   
143.                 propertyName = methodName.substring( "is" .length());   
144.             } else   if (methodName.startsWith( "set" )) {   
145.                 propertyName = methodName.substring( "set" .length());   
146.             }   
147.              return  propertyName ==  null  ?  null  : StringUtils.uncapitalize(propertyName);   
148.         }   
149.     }   
150. }  

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(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<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);
		}
	}
}

 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