1、环境准备

spring boot版本：2.3.1.RELEASE

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网上搜索spring boot 2.x hibernate配置，很多都是jpa例子
从关系上来说应该是spring data jpa-》hibernate-》jpa，jpa是注解规范，jpa是基于hibernate帮我们实现一些通用的操作。
因为需要把旧的项目（spring mvc + spring + hibernat 3.6.5，前后端分离）升级spring boot 2.x，这里只讨论hibernate的配置，毕竟除了hibernate的部分需要升级，其他的部分大部分都可以通用。

2、sessionFactory

hibernate别的不需要多说，只需要设置sessionFactory就可以了。

spring boot可以直接从EntityManagerFactory获取sessionFactory.

下面是修改SimpleHibernateDao的代码，SimpleHibernateDao是旧项目里的封装了常用方法的基类

@Autowired
private EntityManagerFactory entityManagerFactory;
/**
 * 取得sessionFactory.
 */
public SessionFactory getSessionFactory() {
    return entityManagerFactory.unwrap(SessionFactory.class);
}
/**
 * 取得当前Session.
 */
protected Session getSession() {
    return getSessionFactory().getCurrentSession();
}

获取session的2种方式：
1、getCurrentSession()会自动关闭session，但是要配置current_session_context_class，并且需要使用事务
2、openSession()这种方式需要手动关闭session

3、步骤三

前面配置完，测试报no transaction is in progress错误
解决方法1:代码配置

spring.jpa.database=MYSQL
spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=none
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5Dialect
spring.jpa.properties.hibernate.current_session_context_class=org.springframework.orm.hibernate5.SpringSessionContext
spring.jpa.properties.hibernate.show-sql=true
spring.jpa.properties.hibernate.cache.use_second_level_cache=false
spring.jpa.properties.hibernate.cache.use_query_cache=false

@Configuration
public class HibernateConfig {
    @Autowired
    private Environment environment;
   @Autowired
    private DataSource dataSource;
    @Bean
    public LocalSessionFactoryBean sessionFactoryBean() {
        LocalSessionFactoryBean sessionFactoryBean = new LocalSessionFactoryBean();
        sessionFactoryBean.setDataSource(dataSource);
        sessionFactoryBean.setPackagesToScan("com.qizhan100");//dao和entity的公共包
        sessionFactoryBean.setHibernateProperties(hibernateProperties());
        return sessionFactoryBean;
    }
    //获取hibernate配置
    private Properties hibernateProperties() {
        Properties properties = new Properties();
        properties.setProperty("hibernate.current_session_context_class", environment.getProperty("spring.jpa.properties.hibernate.current_session_context_class"));
        properties.setProperty("hibernate.hbm2ddl.auto", environment.getProperty("spring.jpa.hibernate.ddl-auto"));
        properties.setProperty("hibernate.show-sql", environment.getProperty("spring.jpa.properties.hibernate.show-sql"));
        properties.setProperty("hibernate.cache.use_second_level_cache", environment.getProperty("spring.jpa.properties.hibernate.cache.use_second_level_cache"));
        properties.setProperty("hibernate.cache.use_query_cache", environment.getProperty("spring.jpa.properties.hibernate.cache.use_query_cache"));
        return properties;
    }
}

解决方法2：降低hibernate版本

<properties>
    <java.version>1.8</java.version>
    <hibernate.version>5.0.12.Final</hibernate.version>
</properties>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>${hibernate.version}</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-entitymanager</artifactId>
    <version>${hibernate.version}</version>
</dependency>
`

getCurrentSession导致的问题

问题1：org.hibernate.HibernateException: No CurrentSessionContext configured!

application.properties

spring.jpa.properties.hibernate.current_session_context_class=org.springframework.orm.hibernate5.SpringSessionContext

问题2：Could not obtain transaction-synchronized Session for current thread

这个问题就是因为session是用getCurrentSession()获取，但是方法上没有开启事务导致。

consider declaring the factory method as static for independence from its containing instance
待查

参考资料
https://www.jianshu.com/p/57e3c9a40709
https://blog.csdn.net/qq_15329947/article/details/85232287
https://blog.csdn.net/xiaonannew/article/details/82634241
https://blog.csdn.net/wt592376761/article/details/104797009