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

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:

?

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 checkif(!Hibernate.isInitialized(returnValue)) {return null;}//this is Hibernate Objectif(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

1 楼 超级潜水员 2008-10-30 还不错，但hibernate collection的序列化呢？