title: How to save Lists of Lists (List<List<String>> list) in JPA and Hibernate
body: <p>I am using Spring server and JPA to save the variables.</p>
  
  <p>I am trying to save:</p>
  
  <pre><code>@ElementCollection(fetch=FetchType.EAGER)
      List&lt;List&lt;String&gt;&gt; Listarespostas = new ArrayList&lt;List&lt;String&gt;&gt;();
  </code></pre>
  
  <p>But obviously an error appears:</p>
  
  <pre><code>Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class palmaslab.mapas.config.Application: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory
      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1553)
      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
      at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
      at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
      at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
      at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
      at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:973)
      at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:750)
      at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
      at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:120)
      at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:648)
      at org.springframework.boot.SpringApplication.run(SpringApplication.java:311)
      at org.springframework.boot.SpringApplication.run(SpringApplication.java:909)
      at org.springframework.boot.SpringApplication.run(SpringApplication.java:898)
      at palmaslab.mapas.config.Application.main(Application.java:54)
  Caused by: javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory
      at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.persistenceException(EntityManagerFactoryBuilderImpl.java:1225)
      at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.access$600(EntityManagerFactoryBuilderImpl.java:119)
      at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:853)
      at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:843)
      at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.withTccl(ClassLoaderServiceImpl.java:399)
      at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:842)
      at org.hibernate.jpa.HibernatePersistenceProvider.createContainerEntityManagerFactory(HibernatePersistenceProvider.java:150)
      at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:336)
      at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:318)
      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1612)
      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549)
      ... 15 more
  Caused by: org.hibernate.MappingException: Could not determine type for: java.util.List, at table: Project_Listarespostas, for columns: [org.hibernate.mapping.Column(Listarespostas)]
      at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:336)
      at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:310)
      at org.hibernate.mapping.Collection.validate(Collection.java:315)
      at org.hibernate.cfg.Configuration.validate(Configuration.java:1362)
      at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1849)
      at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:850)
  </code></pre>
  
  <p>Anyone knows an alternative?</p>