SpringBoot集成Spring Data JPA

JPA是什麼

JPA(Java Persistence API)是Sun官方提出的Java持久化規範,它爲Java開發人員提供了一種對象/關聯映射工具 來管理Java應用中的關係數據.它包括以下幾方面的內容:

1.ORM映射 支持xml和註解方式建立實體與表之間的映射.

2.Java持久化API 定義了一些常用的CRUD接口,我們只需直接調用,而不需要考慮底層JDBC和SQL的細節.

3.JPQL查詢語言 這是持久化操作中很重要的一個方面，通過面向對象而非面向數據庫的查詢語言查詢數據，避免程序的SQL語句緊密耦合.

在工作中,我們都會用到ORM技術,比如Hibernate,JOOQ等,根據需求的不同,我們會採用不同的ORM框架,當我們需要 更換ORM框架來滿足我們的需求時,由於不同ORM框架的實現,使用方式的區別以及各自爲營,我們往往需要對代碼進行重構.JPA的 出現就是爲了解決這個問題,JPA充分吸收了現有一些ORM框架的優點,具有易於使用，伸縮性強等優點,爲ORM技術提供了一套標準的 接口用來整合不同的ORM框架.

Hibernate對JPA的實現

JPA本身並不做具體的實現,而只是定義了一些接口規範,讓其它ORM來具體的實現這些接口,就目前來說,對JPA規範實現最好的就是 Hibernate了.這裏提一下Mybatis,Mybatis並沒有實現JPA規範,它本身也不能算做一個真正的ORM框架.

Spring Data JPA是什麼

Spring Data JPA只是Spring Data框架的一個模塊,可以極大的簡化JPA的使用,Spring Data JPA強大的地方還在於能夠簡化我們 對持久層業務邏輯的開發,通過規範持久層方法的名稱,通過名稱來判斷需要實現什麼業務邏輯,我們機會可以在不寫一句sql,不做任何dao層 邏輯的情況下完成我們絕大部分的開發,當然,對於一些複雜的,性能要求高的查詢,Spring Data JPA一樣支持我們使用原生的sql.

在這裏我們不過多的去介紹JPA以及Spring Data JPA,主要還是與SpringBoot集成的一些細節以及示例.

引入依賴

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<!-- 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>

我們引入這個依賴後,發現也引入了Hibernate的包,這是現在一種默認的做法,Hibernate已經被作爲JPA規範的最好實現了,這裏就不介紹Druid數據源的 配置了,大家可以看另外一篇XXXX.

配置我們的數據源以及JPA(Hibernate)

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#配置模板 #https://docs.spring.io/spring-boot/docs/1.4.0.RELEASE/reference/html/common-application-properties.html #數據源 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.Driver spring.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,具體說明可以看README spring.jpa.hibernate.ddl-auto=update #通過方法名解析sql的策略,具體說明可以看README,這裏就不配置了 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數據源注入

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@Configuration publicclassDruidDataSourceConfig {   /**    * DataSource 配置    * @return    */   @ConfigurationProperties(prefix = "spring.datasource.druid.read")   @Bean(name = "readDruidDataSource")   publicDataSource readDruidDataSource() {     returnnewDruidDataSource();   }   /**    * DataSource 配置    * @return    */   @ConfigurationProperties(prefix = "spring.datasource.druid.write")   @Bean(name = "writeDruidDataSource")   @Primary   publicDataSource writeDruidDataSource() {     returnnewDruidDataSource();   } }

EntityManagerFactory實例注入

EntityManagerFactory類似於Hibernate的SessionFactory,mybatis的SqlSessionFactory 總之,在執行操作之前,我們總要獲取一個EntityManager,這就類似於Hibernate的Session, mybatis的sqlSession. 注入EntityManagerFactory有兩種方式,一種是直接注入EntityManagerFactory,另一種是通過 LocalContainerEntityManagerFactoryBean來間接注入.雖說這兩種方法都是基於 LocalContainerEntityManagerFactoryBean的,但是在配置上還是有一些區別.

1.直接注入EntityManagerFactory

配置:通過spring.jpa.properties.*來配置Hibernate的屬性

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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") publicclassWriteDataSourceConfig {   @Autowired   JpaProperties jpaProperties;   @Autowired   @Qualifier("writeDruidDataSource")   privateDataSource writeDruidDataSource;   /**    * EntityManagerFactory類似於Hibernate的SessionFactory,mybatis的SqlSessionFactory    * 總之,在執行操作之前,我們總要獲取一個EntityManager,這就類似於Hibernate的Session,    * mybatis的sqlSession.    * @return    */   @Bean(name = "writeEntityManagerFactory")   @Primary   publicEntityManagerFactory writeEntityManagerFactory() {     HibernateJpaVendorAdapter vendorAdapter = newHibernateJpaVendorAdapter();     LocalContainerEntityManagerFactoryBean factory = newLocalContainerEntityManagerFactoryBean();     factory.setJpaVendorAdapter(vendorAdapter);     factory.setPackagesToScan("com.lc.springBoot.jpa.entity");     factory.setDataSource(writeDruidDataSource);//數據源     factory.setJpaPropertyMap(jpaProperties.getProperties());     factory.afterPropertiesSet();//在完成了其它所有相關的配置加載以及屬性設置後,才初始化     returnfactory.getObject();   }   /**    * 配置事物管理器    * @return    */   @Bean(name = "writeTransactionManager")   @Primary   publicPlatformTransactionManager writeTransactionManager() {     JpaTransactionManager jpaTransactionManager = newJpaTransactionManager();     jpaTransactionManager.setEntityManagerFactory(this.writeEntityManagerFactory());     returnjpaTransactionManager;   } }

2.先注入LocalContainerEntityManagerFactoryBean,再獲取EntityManagerFactory

配置:

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spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialect spring.jpa.database=mysql spring.jpa.generate-ddl=true #就是hibernate.hbm2ddl.auto,具體說明可以看README spring.jpa.hibernate.ddl-auto=update #通過方法名解析sql的策略,具體說明可以看README,這裏就不配置了 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") publicclassWriteDataSourceConfig1 {   @Autowired   JpaProperties jpaProperties;   @Autowired   @Qualifier("writeDruidDataSource")   privateDataSource writeDruidDataSource;   /**    * 我們通過LocalContainerEntityManagerFactoryBean來獲取EntityManagerFactory實例    * @return    */   @Bean(name = "writeEntityManagerFactoryBean")   @Primary   publicLocalContainerEntityManagerFactoryBean writeEntityManagerFactoryBean(EntityManagerFactoryBuilder builder) {     returnbuilder         .dataSource(writeDruidDataSource)         .properties(jpaProperties.getProperties())         .packages("com.lc.springBoot.jpa.entity")//設置實體類所在位置         .persistenceUnit("writePersistenceUnit")         .build();     //.getObject();//不要在這裏直接獲取EntityManagerFactory   }   /**    * EntityManagerFactory類似於Hibernate的SessionFactory,mybatis的SqlSessionFactory    * 總之,在執行操作之前,我們總要獲取一個EntityManager,這就類似於Hibernate的Session,    * mybatis的sqlSession.    * @param builder    * @return    */   @Bean(name = "writeEntityManagerFactory")   @Primary   publicEntityManagerFactory writeEntityManagerFactory(EntityManagerFactoryBuilder builder) {     returnthis.writeEntityManagerFactoryBean(builder).getObject();   }   /**    * 配置事物管理器    * @return    */   @Bean(name = "writeTransactionManager")   @Primary   publicPlatformTransactionManager writeTransactionManager(EntityManagerFactoryBuilder builder) {     returnnewJpaTransactionManager(writeEntityManagerFactory(builder));   } }

對於這個配置

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@Bean(name = "writeEntityManagerFactoryBean")   @Primary   publicLocalContainerEntityManagerFactoryBean writeEntityManagerFactoryBean(EntityManagerFactoryBuilder builder) {     returnbuilder         .dataSource(writeDruidDataSource)         .properties(jpaProperties.getProperties())         .packages("com.lc.springBoot.jpa.entity")//設置實體類所在位置         .persistenceUnit("writePersistenceUnit")         .build();     //.getObject();//不要在這裏直接獲取EntityManagerFactory   }

getObject()方法可以獲取到EntityManagerFactory的實例,看似跟第一種沒有什麼區別,但是我們不能直接用 getObject(),不然會獲取不到,報空指針異常.

讀寫分離配置

自定義注入AbstractRoutingDataSource

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@Configuration publicclassDataSourceConfig {   privatefinalstatic String WRITE_DATASOURCE_KEY = "writeDruidDataSource";   privatefinalstatic String READ_DATASOURCE_KEY = "readDruidDataSource";   /**    * 注入AbstractRoutingDataSource    * @param readDruidDataSource    * @param writeDruidDataSource    * @return    * @throws Exception    */   @Bean   publicAbstractRoutingDataSource routingDataSource(       @Qualifier(READ_DATASOURCE_KEY) DataSource readDruidDataSource,       @Qualifier(WRITE_DATASOURCE_KEY) DataSource writeDruidDataSource   )throwsException {     DynamicDataSource dataSource = newDynamicDataSource();     Map<Object, Object> targetDataSources = newHashMap();     targetDataSources.put(WRITE_DATASOURCE_KEY, writeDruidDataSource);     targetDataSources.put(READ_DATASOURCE_KEY, readDruidDataSource);     dataSource.setTargetDataSources(targetDataSources);     dataSource.setDefaultTargetDataSource(writeDruidDataSource);     returndataSource;   } }

自定義註解

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@Target({ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented public@interfaceTargetDataSource {   String dataSource() default"";//數據源 }

使用ThreadLocal使數據源與線程綁定

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publicclassDynamicDataSourceHolder {    //使用ThreadLocal把數據源與當前線程綁定    privatestaticfinal ThreadLocal<String> dataSources = newThreadLocal<String>();    publicstaticvoid setDataSource(String dataSourceName) {      dataSources.set(dataSourceName);    }    publicstaticString getDataSource() {      return(String) dataSources.get();    }    publicstaticvoid clearDataSource() {      dataSources.remove();    }  }  publicclassDynamicDataSource extendsAbstractRoutingDataSource {    @Override    protectedObject determineCurrentLookupKey() {      //可以做一個簡單的負載均衡策略      String lookupKey = DynamicDataSourceHolder.getDataSource();      System.out.println("------------lookupKey---------"+lookupKey);      returnlookupKey;    }  }

定義切面

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@Aspect   @Component   publicclassDynamicDataSourceAspect {     @Around("execution(public * com.lc.springBoot.jpa.service..*.*(..))")     publicObject around(ProceedingJoinPoint pjp) throwsThrowable {       MethodSignature methodSignature = (MethodSignature) pjp.getSignature();       Method targetMethod = methodSignature.getMethod();       if(targetMethod.isAnnotationPresent(TargetDataSource.class)) {         String targetDataSource = targetMethod.getAnnotation(TargetDataSource.class).dataSource();         System.out.println("----------數據源是:"+ targetDataSource + "------");         DynamicDataSourceHolder.setDataSource(targetDataSource);       }       Object result = pjp.proceed();//執行方法       DynamicDataSourceHolder.clearDataSource();       returnresult;     }   }