碼上快樂

相關內容    簡體    繁體

SpringBoot JPA懶加載異常 - com.fasterxml.jackson.databind.JsonMappingException: could not initialize proxy

本文轉載自   查看原文   2019-10-24 08:50   332    Java相關框架

問題與分析

某日忽然發現在用postman測試數據時報錯如下：

com.fasterxml.jackson.databind.JsonMappingException: could not initialize proxy [com.cbxsoftware.cbx.attachment.entity.RefAttachment#c109ec36e60c4a89a10eabc72416d984] - no Session (through reference chain: com.cbxsoftware.cbx.sampletracker.elasticsearch.entity.SampleTrackerDetailEstc["sampleTracker"]->com.cbxsoftware.cbx.sampletracker.elasticsearch.entity.SampleTrackerEstc["sampleTracker"]->com.cbxsoftware.cbx.sampletracker.entity.SampleTracker["item"]->com.cbxsoftware.cbx.item.entity.RefItem["image"]->com.cbxsoftware.cbx.image.entity.RefImage["propFormat"]->com.cbxsoftware.cbx.attachment.entity.RefAttachment$HibernateProxy$uNA5RwMT["revision"])
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:394)
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:353)
	at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:316)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:727)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.impl.UnwrappingBeanSerializer.serialize(UnwrappingBeanSerializer.java:120)
	at com.fasterxml.jackson.databind.ser.impl.UnwrappingBeanPropertyWriter.serializeAsField(UnwrappingBeanPropertyWriter.java:127)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
	at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3905)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3219)
	...
Caused by: org.hibernate.LazyInitializationException: could not initialize proxy [com.cbxsoftware.cbx.attachment.entity.RefAttachment#c109ec36e60c4a89a10eabc72416d984] - no Session
	at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:169)
	at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:309)
	at org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor.intercept(ByteBuddyInterceptor.java:45)
	at org.hibernate.proxy.ProxyConfiguration$InterceptorDispatcher.intercept(ProxyConfiguration.java:95)
	at com.cbxsoftware.cbx.attachment.entity.RefAttachment$HibernateProxy$uNA5RwMT.getRevision(Unknown Source)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:688)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	... 128 common frames omitted

報錯很明顯，是由於hibernate的懶加載引起的。項目使用的是SpringBoot框架，JPA默認使用的是hibernate的實現，而hibernate的懶加載機制其實就是延遲加載對象，如果沒有在session關閉前使用到對象里除id以外的屬性時，就只會返回一個沒有初始化過的包含了id的代理類。很多時候，這個代理類會引發上述的異常。

簡單說一下為什么會觸發懶加載異常，首先hibernate開啟一個session（會話），然后開啟transaction（事務），接着發出sql找回數據並組裝成pojo（或者說entity、model），這時候如果pojo里有懶加載的對象，並不會去發出sql查詢db，而是直接返回一個懶加載的代理對象，這個對象里只有id。如果接下來沒有其他的操作去訪問這個代理對象除了id以外的屬性，就不會去初始化這個代理對象，也就不會去發出sql查找db。接着事務提交，session關閉。如果這時候再去訪問代理對象除了id以外的屬性時，就會報上述的懶加載異常，原因是這時候已經沒有session了，無法初始化懶加載的代理對象。

解決方法一

如果是spring繼承的hibernate，根據上述的原因，可以延長session的生命周期，但是這里用的是SpringBoot的JPA，處理方法不同，需要在application.properties配置下懶加載相關的東西：

spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true

進行該配置后，可以在session關閉時也能另外開啟一個新的session和事務來訪問db以取回懶加載對象的數據。

解決方法二

因為該懶加載異常是缺少session導致的，那么可以通過在方法前添加事務注解@Transactional的方式來解決，只要事務沒有提交，session就不會關閉，自然就不會出現上述的懶加載異常。不過由於該事務注解是用Spring AOP實現的，存在着一些坑，比如類內直接調用無效或者對非public方法無效等，需要多加注意。

當使用了上述兩種方法后，發現不再觸發LazyInitializationException，但是卻發生了另一個新的異常InvalidDefinitionException：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: com.cbxsoftware.cbx.item.elasticsearch.entity.ItemEstc["mainEntity"]->com.cbxsoftware.cbx.item.entity.Item["image"]->com.cbxsoftware.cbx.image.entity.RefImage["propFormat"]->com.cbxsoftware.cbx.attachment.entity.RefAttachment$HibernateProxy$vTKSYzrN["hibernateLazyInitializer"])
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77)
	at com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1191)
	at com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:313)
	at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:71)
	at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:33)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.impl.UnwrappingBeanSerializer.serialize(UnwrappingBeanSerializer.java:120)
	at com.fasterxml.jackson.databind.ser.impl.UnwrappingBeanPropertyWriter.serializeAsField(UnwrappingBeanPropertyWriter.java:127)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
	at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3905)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3219)
	...

這個異常是由於hibernate在代理類里添加了一個屬性hibernateLazyInitializer，當該對象轉換成json的時候就會報錯。解決方法是將該屬性過濾掉，可以在對應的類名或者公共類前加上如下注解：

@JsonIgnoreProperties(value = { "hibernateLazyInitializer" })

源碼分析

因為對懶加載異常的發生有些好奇，所以看了下hibernate的源碼，這里簡單分析下，另外我看的是兩個源碼包如下：

spring-orm-5.1.5.RELEASE.jar
hibernate-core-5.3.7.Final.jar

首先是關於spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true的配置，前面半截是因為JPA集成了hibernate的配置，所以在hibernate中，這個配置應該是hibernate.enable_lazy_load_no_trans=true。

在hibernate的一個常量接口org.hibernate.cfg.AvailableSettings中定義了各種配置常量，其中就包括上述這個配置：

String ENABLE_LAZY_LOAD_NO_TRANS = "hibernate.enable_lazy_load_no_trans";

在啟動項目的時候會讀取配置文件，將其解析為一個HashMap<K,V>，這些參數在newEntityManagerFactoryBuilderImpl的時候被使用到，上面的常量會在org.hibernate.boot.internal.SessionFactoryOptionsBuilder里被拿來初始化：

this.initializeLazyStateOutsideTransactions = cfgService.getSetting( ENABLE_LAZY_LOAD_NO_TRANS, BOOLEAN, false );

因為在配置文件里配置了該變量的值為true，所以這里在初始化的時候就會把initializeLazyStateOutsideTransactions的值設置為true。該變量由一個方法來判斷其值是否為true：

	@Override
	public boolean isInitializeLazyStateOutsideTransactionsEnabled() {
		return initializeLazyStateOutsideTransactions;
	}

接着在組裝pojo時，會為懶加載對象創建對應的代理對象，當需要獲取該代理對象除id以外的屬性時，就會調用AbstractLazyInitializer#initialize()進行初始化，邏輯如下：

	@Override
	public final void initialize() throws HibernateException {
		if ( !initialized ) {
			if ( allowLoadOutsideTransaction ) {
				permissiveInitialization();
			}
			else if ( session == null ) {
				throw new LazyInitializationException( "could not initialize proxy [" + entityName + "#" + id + "] - no Session" );
			}
			else if ( !session.isOpen() ) {
				throw new LazyInitializationException( "could not initialize proxy [" + entityName + "#" + id + "] - the owning Session was closed" );
			}
			else if ( !session.isConnected() ) {
				throw new LazyInitializationException( "could not initialize proxy [" + entityName + "#" + id + "] - the owning Session is disconnected" );
			}
			else {
				target = session.immediateLoad( entityName, id );
				initialized = true;
				checkTargetState(session);
			}
		}
		else {
			checkTargetState(session);
		}
	}

如果在配置文件中設置了spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true，那么上述的allowLoadOutsideTransaction變量值就為true，則可以進入permissiveInitialization()方法另起session和事務，最終避免懶加載異常LazyInitializationException。如果沒有配置該參數，那么就會由於session已關閉（即為null）而拋出LazyInitializationException。

參考鏈接


免責聲明！

本站轉載的文章為個人學習借鑒使用，本站對版權不負任何法律責任。如果侵犯了您的隱私權益，請聯系本站郵箱yoyou2525@163.com刪除。



猜您在找 com.fasterxml.jackson.databind.JsonMappingException 【jackson 異常】com.fasterxml.jackson.databind.JsonMappingException異常處理 HttpMessageNotWritableException: Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class 解決com.fasterxml.jackson.databind.JsonMappingException: No suitable com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class jackson報錯：com.fasterxml.jackson.databind.JsonMappingException: Incompatible Jackson version: 2.9.6 com.fasterxml.jackson.databind.JsonMappingException: No content to map due to end-of-input java報錯：com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize out of START_ARRAY token Caused by :java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.JsonMappingException
 
粵ICP備18138465號   © 2018-2025 CODEPRJ.COM