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发表时间:2008-10-29
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.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 声明:ITeye文章版权属于作者,受法律保护。没有作者书面许可不得转载。
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发表时间:2008-10-30
还不错,但hibernate collection的序列化呢?
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