springboot jpa sql打印_SpringBoot集成Spring Data JPA以及读写分离

JPA是什么

JPA(Java Persistence API)是Sun官方提出的Java持久化规范,它为Java开发人员提供了一种对象/关联映射工具来管理Java应用中的关系数据.它包括以下几方面的内容:

1.ORM映射支持xml和注解方式建立实体与表之间的映射.
2.Java持久化API 定义了一些常用的CRUD接口,我们只需直接调用,而不需要考虑底层JDBC和SQL的细节.
3.JPQL查询语言这是持久化操作中很重要的一个方面，通过面向对象而非面向数据库的查询语言查询数据，避免程序的SQL语句紧密耦合.
在工作中,我们都会用到ORM技术,比如Hibernate,JOOQ等,根据需求的不同,我们会采用不同的ORM框架,当我们需要更换ORM框架来满足我们的需求时,由于不同ORM框架的实现,使用方式的区别以及各自为营,我们往往需要对代码进行重构.JPA的出现就是为了解决这个问题,JPA充分吸收了现有一些ORM框架的优点,具有易于使用，伸缩性强等优点,为ORM技术提供了一套标准的接口用来整合不同的ORM框架.

Hibernate对JPA的实现

JPA本身并不做具体的实现,而只是定义了一些接口规范,让其它ORM来具体的实现这些接口,就目前来说,对JPA规范实现最好的就是 Hibernate了.这里提一下Mybatis,Mybatis并没有实现JPA规范,它本身也不能算做一个真正的ORM框架.

Spring Data JPA是什么

Spring Data JPA只是Spring Data框架的一个模块,可以极大的简化JPA的使用,Spring Data JPA强大的地方还在于能够简化我们对持久层业务逻辑的开发,通过规范持久层方法的名称,通过名称来判断需要实现什么业务逻辑,我们机会可以在不写一句sql,不做任何dao层逻辑的情况下完成我们绝大部分的开发,当然,对于一些复杂的,性能要求高的查询,Spring Data JPA一样支持我们使用原生的sql.

在这里我们不过多的去介绍JPA以及Spring Data JPA,主要还是与SpringBoot集成的一些细节以及示例.

引入依赖

<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-jpa -->
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

我们引入这个依赖后,发现也引入了Hibernate的包,这是现在一种默认的做法,Hibernate已经被作为JPA规范的最好实现了.

配置我们的数据源以及JPA(Hibernate)

#配置模板
#https://docs.spring.io/spring-boot/docs/1.4.0.RELEASE/reference/html/common-application-properties.html#数据源
spring.datasource.druid.write.url=jdbc:mysql://localhost:3306/jpa
spring.datasource.druid.write.username=root
spring.datasource.druid.write.password=1
spring.datasource.druid.write.driver-class-name=com.mysql.jdbc.Driverspring.datasource.druid.read.url=jdbc:mysql://localhost:3306/jpa
spring.datasource.druid.read.username=root
spring.datasource.druid.read.password=1
spring.datasource.druid.read.driver-class-name=com.mysql.jdbc.Driver#JPA (JpaBaseConfiguration, HibernateJpaAutoConfiguration)
spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialect
spring.jpa.database=mysql
spring.jpa.generate-ddl=true
#就是hibernate.hbm2ddl.auto,具体说明可以看README
spring.jpa.hibernate.ddl-auto=update
#通过方法名解析sql的策略
spring.jpa.hibernate.naming-strategy=org.hibernate.cfg.DefaultComponentSafeNamingStrategy
spring.jpa.show-sql=true
#spring.jpa.properties.*
#spring.jpa.properties.hibernate.hbm2ddl.auto=update
#spring.jpa.properties.hibernate.show_sql=true
#spring.jpa.properties.hibernate.use-new-id-generator-mappings=true

druid数据源注入

@Configuration
public class DruidDataSourceConfig {/*** DataSource 配置* @return*/@ConfigurationProperties(prefix = "spring.datasource.druid.read")@Bean(name = "readDruidDataSource")public DataSource readDruidDataSource() {return new DruidDataSource();}/*** DataSource 配置* @return*/@ConfigurationProperties(prefix = "spring.datasource.druid.write")@Bean(name = "writeDruidDataSource")@Primarypublic DataSource writeDruidDataSource() {return new DruidDataSource();}
}

EntityManagerFactory实例注入

EntityManagerFactory类似于Hibernate的SessionFactory,mybatis的SqlSessionFactory 总之,在执行操作之前,我们总要获取一个EntityManager,这就类似于Hibernate的Session, mybatis的sqlSession. 注入EntityManagerFactory有两种方式,一种是直接注入EntityManagerFactory,另一种是通过 LocalContainerEntityManagerFactoryBean来间接注入.虽说这两种方法都是基于 LocalContainerEntityManagerFactoryBean的,但是在配置上还是有一些区别.

1.直接注入EntityManagerFactory

配置:通过spring.jpa.properties.*来配置Hibernate的属性

spring.jpa.properties.hibernate.hbm2ddl.auto=update
spring.jpa.properties.hibernate.show_sql=true
spring.jpa.properties.hibernate.use-new-id-generator-mappings=true
@Configuration
@EnableJpaRepositories(value = "com.lc.springBoot.jpa.repository",entityManagerFactoryRef = "writeEntityManagerFactory",transactionManagerRef="writeTransactionManager")
public class WriteDataSourceConfig {@AutowiredJpaProperties jpaProperties;@Autowired@Qualifier("writeDruidDataSource")private DataSource writeDruidDataSource;/*** EntityManagerFactory类似于Hibernate的SessionFactory,mybatis的SqlSessionFactory* 总之,在执行操作之前,我们总要获取一个EntityManager,这就类似于Hibernate的Session,* mybatis的sqlSession.* @return*/@Bean(name = "writeEntityManagerFactory")@Primarypublic EntityManagerFactory writeEntityManagerFactory() {HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();factory.setJpaVendorAdapter(vendorAdapter);factory.setPackagesToScan("com.lc.springBoot.jpa.entity");factory.setDataSource(writeDruidDataSource);//数据源factory.setJpaPropertyMap(jpaProperties.getProperties());factory.afterPropertiesSet();//在完成了其它所有相关的配置加载以及属性设置后,才初始化return factory.getObject();}/*** 配置事物管理器* @return*/@Bean(name = "writeTransactionManager")@Primarypublic PlatformTransactionManager writeTransactionManager() {JpaTransactionManager jpaTransactionManager = new JpaTransactionManager();jpaTransactionManager.setEntityManagerFactory(this.writeEntityManagerFactory());return jpaTransactionManager;}
}

2.先注入LocalContainerEntityManagerFactoryBean,再获取EntityManagerFactory

配置:

spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialect
spring.jpa.database=mysql
spring.jpa.generate-ddl=true
#就是hibernate.hbm2ddl.auto,具体说明可以看README
spring.jpa.hibernate.ddl-auto=update
#通过方法名解析sql的策略,具体说明可以看README,这里就不配置了
spring.jpa.hibernate.naming-strategy=org.hibernate.cfg.DefaultComponentSafeNamingStrategy
spring.jpa.show-sql=true
@Configuration
@EnableJpaRepositories(value = "com.lc.springBoot.jpa.repository",entityManagerFactoryRef = "writeEntityManagerFactory",transactionManagerRef = "writeTransactionManager")
public class WriteDataSourceConfig1 {@AutowiredJpaProperties jpaProperties;@Autowired@Qualifier("writeDruidDataSource")private DataSource writeDruidDataSource;/*** 我们通过LocalContainerEntityManagerFactoryBean来获取EntityManagerFactory实例* @return*/@Bean(name = "writeEntityManagerFactoryBean")@Primarypublic LocalContainerEntityManagerFactoryBean writeEntityManagerFactoryBean(EntityManagerFactoryBuilder builder) {return builder.dataSource(writeDruidDataSource).properties(jpaProperties.getProperties()).packages("com.lc.springBoot.jpa.entity") //设置实体类所在位置.persistenceUnit("writePersistenceUnit").build();//.getObject();//不要在这里直接获取EntityManagerFactory}/*** EntityManagerFactory类似于Hibernate的SessionFactory,mybatis的SqlSessionFactory* 总之,在执行操作之前,我们总要获取一个EntityManager,这就类似于Hibernate的Session,* mybatis的sqlSession.* @param builder* @return*/@Bean(name = "writeEntityManagerFactory")@Primarypublic EntityManagerFactory writeEntityManagerFactory(EntityManagerFactoryBuilder builder) {return this.writeEntityManagerFactoryBean(builder).getObject();}/*** 配置事物管理器* @return*/@Bean(name = "writeTransactionManager")@Primarypublic PlatformTransactionManager writeTransactionManager(EntityManagerFactoryBuilder builder) {return new JpaTransactionManager(writeEntityManagerFactory(builder));}
}

对于这个配置

@Bean(name = "writeEntityManagerFactoryBean")@Primarypublic LocalContainerEntityManagerFactoryBean writeEntityManagerFactoryBean(EntityManagerFactoryBuilder builder) {return builder.dataSource(writeDruidDataSource).properties(jpaProperties.getProperties()).packages("com.lc.springBoot.jpa.entity") //设置实体类所在位置.persistenceUnit("writePersistenceUnit").build();//.getObject();//不要在这里直接获取EntityManagerFactory}

getObject()方法可以获取到EntityManagerFactory的实例,看似跟第一种没有什么区别,但是我们不能直接用 getObject(),不然会获取不到,报空指针异常.

读写分离配置

自定义注入AbstractRoutingDataSource

@Configuration
public class DataSourceConfig {private final static String WRITE_DATASOURCE_KEY = "writeDruidDataSource";private final static String READ_DATASOURCE_KEY = "readDruidDataSource";/*** 注入AbstractRoutingDataSource* @param readDruidDataSource* @param writeDruidDataSource* @return* @throws Exception*/@Beanpublic AbstractRoutingDataSource routingDataSource(@Qualifier(READ_DATASOURCE_KEY) DataSource readDruidDataSource,@Qualifier(WRITE_DATASOURCE_KEY) DataSource writeDruidDataSource) throws Exception {DynamicDataSource dataSource = new DynamicDataSource();Map<Object, Object> targetDataSources = new HashMap();targetDataSources.put(WRITE_DATASOURCE_KEY, writeDruidDataSource);targetDataSources.put(READ_DATASOURCE_KEY, readDruidDataSource);dataSource.setTargetDataSources(targetDataSources);dataSource.setDefaultTargetDataSource(writeDruidDataSource);return dataSource;}
}

自定义注解

@Target({ElementType.METHOD, ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface TargetDataSource {String dataSource() default "";//数据源}

使用ThreadLocal使数据源与线程绑定

public class DynamicDataSourceHolder {//使用ThreadLocal把数据源与当前线程绑定private static final ThreadLocal<String> dataSources = new ThreadLocal<String>();public static void setDataSource(String dataSourceName) {dataSources.set(dataSourceName);}public static String getDataSource() {return (String) dataSources.get();}public static void clearDataSource() {dataSources.remove();}}
public class DynamicDataSource extends AbstractRoutingDataSource {@Overrideprotected Object determineCurrentLookupKey() {//可以做一个简单的负载均衡策略String lookupKey = DynamicDataSourceHolder.getDataSource();System.out.println("------------lookupKey---------"+lookupKey);return lookupKey;}}

定义切面

@Aspect@Componentpublic class DynamicDataSourceAspect {@Around("execution(public * com.lc.springBoot.jpa.service..*.*(..))")public Object around(ProceedingJoinPoint pjp) throws Throwable {MethodSignature methodSignature = (MethodSignature) pjp.getSignature();Method targetMethod = methodSignature.getMethod();if (targetMethod.isAnnotationPresent(TargetDataSource.class)) {String targetDataSource = targetMethod.getAnnotation(TargetDataSource.class).dataSource();System.out.println("----------数据源是:" + targetDataSource + "------");DynamicDataSourceHolder.setDataSource(targetDataSource);}Object result = pjp.proceed();//执行方法DynamicDataSourceHolder.clearDataSource();return result;}}

原文链接：https://my.oschina.net/lengchuan/blog/882391

作者：轻易科技-轻易贷研发部李水军