https://docs.jboss.org/hibernate/orm/5.3/userguide/html_single/Hibernate_User_Guide.html

JPA 中很多方法的反射调用已经利用了 MethodHandle 做优化

Background

Spring Boot 自动装配

pkg org.springframework.boot.autoconfigure.orm.jpa

• JpaBaseConfiguration
• HibernateJpaAutoConfiguration

pkg org.springframework.boot.autoconfigure.data.jpa

• JpaRepositoriesAutoConfiguration
  • JpaRepositoriesRegistrar 注册 JPA @Repository
  • RepositoryConfigurationExtension#registerBeansForRoot 会注册一个有意思 BeanPostProcessor, 作用是提供一个工厂方法生产所有的 EntityManagerFactory bean, 将其调用代理至 SharedEntityManagerCreator$SharedEntityManagerInvocationHandler#invoke
    • EntityManagerBeanDefinitionRegistrarPostProcessor, BeanFactoryPostProcessor to register a SharedEntityManagerCreator for every EntityManagerFactory bean definition found in the application context to enable EntityManager instances into constructor arguments. Adds the EntityManagerFactory bean name as qualifier to the EntityManager BeanDefinition to enable explicit references in case of multiple EntityManagerFactory instances.
    • SharedEntityManagerCreator A shared EntityManager will behave just like an EntityManager fetched from* an application server's JNDI environment, as defined by the JPA specification.* It will delegate all calls to the current transactional EntityManager, if any;* otherwise it will fall back to a newly created EntityManager per operation.

EntityManager

EntityManagerFactoryBean

由 LocalContainerEntityManagerFactoryBean 装配产生一个符合 JPA 规范的 javax.persistence.EntityManagerFactory

// 类信息
package org.springframework.orm.jpa;
public class LocalContainerEntityManagerFactoryBean extends AbstractEntityManagerFactoryBean
		implements ResourceLoaderAware, LoadTimeWeaverAware

public abstract class AbstractEntityManagerFactoryBean implements
		FactoryBean<EntityManagerFactory>, BeanClassLoaderAware, BeanFactoryAware, BeanNameAware,
		InitializingBean, DisposableBean, EntityManagerFactoryInfo, PersistenceExceptionTranslator, Serializable
// 流程
LocalContainerEntityManagerFactoryBean#afterPropertiesSet
- 加载一个 Spring PersistenceUnitManager 提供 javax.persistence.spi.PersistenceUnitInfo, Manager 主要(Supports standard JPA scanning for {@code persistence.xml} files,
 * with configurable file locations, JDBC DataSource lookup and load-time weaving.)(即包含了项目配置的 Model, Converter, JDBC, 切面增强等)
- 加载 org.springframework.orm.jpa.JpaVendorAdapter, 提供 JPA 实现的具体配置 ()
AbstractEntityManagerFactoryBean#afterPropertiesSet (super)
- 从 JpaVendorAdapter 获取 javax.persistence.spi.PersistenceProvider (SpringHibernateJpaPersistenceProvider)
- 从 JpaVendorAdapter 获取 Class<? extends EntityManagerFactory> entityManagerFactoryInterface
- 从 JpaVendorAdapter 获取 Class<? extends EntityManager> entityManagerInterface
- 从 JpaVendorAdapter 获取 JpaDialect (#releaseJdbcConnection, #getJdbcConnection, #cleanupTransaction, #prepareTransaction, #beginTransaction)
- 为 this 设置 PersistenceProvider, jpaPropertyMap, Class entityManagerFactoryInterface, Class entityManagerInterface,
   JpaDialect
- this.nativeEntityManagerFactory = createNativeEntityManagerFactory, 使用 PersistenceProvider#createContainerEntityManagerFactor(PersistenceUnitInfo,Map jpaProperties) 
    创建 EntityManagerFactory(由 class org.hibernate.internal.SessionFactoryImpl) 

- this.entityManagerFactory = createEntityManagerFactoryProxy(this.nativeEntityManagerFactory);
   代理 LocalContainerEntityManagerFactoryBean, 生成具有事务 ManagedEntityManagerFactoryInvocationHandler, 
   每个调用均会被代理至 AbstractEntityManagerFactoryBean#invokeProxyMethod

AbstractJpaVendorAdapter (created by JpaBaseConfiguration, HibernateJpaConfiguration)

// 三属性 spring.jpa.showSql, spring.jpa.database.*, spring.jpa.generateDdl
this.persistenceProvider = new SpringHibernateJpaPersistenceProvider();
this.entityManagerFactoryInterface = org.hibernate.jpa.HibernateEntityManagerFactory.class;
this.entityManagerInterface = org.hibernate.jpa.HibernateEntityManager.class;
adapter.setShowSql(this.properties.isShowSql());
adapter.setDatabase(this.properties.getDatabase());	
adapter.setDatabasePlatform(this.properties.getDatabasePlatform());
adapter.setGenerateDdl(this.properties.isGenerateDdl());

EntityManager

Spring 会调用由 org.springframework.orm.jpa.SharedEntityManagerCreator 生成 SpringContext 管理的 EntityManager 代理

A shared EntityManager will behave just like an EntityManager fetched from
 * an application server's JNDI environment, as defined by the JPA specification.
 * It will delegate all calls to the current transactional EntityManager, if any;
 * otherwise it will fall back to a newly created EntityManager per operation.

或者由 ExtendedEntityManagerCreator 生成外部管理的 EntityManager 代理