JPA是什么
JPA(Java Persistence API)是Sun官方提出的Java持久化規范,它為Java開發人員提供了一種對象/關聯映射工具 來管理Java應用中的關系數據.它包括以下幾方面的內容:
1.ORM映射 支持xml和注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,我們會采用不同的ORM框架,當我們需要 更換ORM框架來滿足我們的需求時,由于不同ORM框架的實現,使用方式的區別以及各自為營,我們往往需要對代碼進行重構.JPA的 出現就是為了解決這個問題,JPA充分吸收了現有一些ORM框架的優點,具有易于使用，伸縮性強等優點,為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本身并不做具體的實現,而只是定義了一些接口規范,讓其它ORM來具體的實現這些接口,就目前來說,對JPA規范實現最好的就是 Hibernate了.這里提一下Mybatis,Mybatis并沒有實現JPA規范,它本身也不能算做一個真正的ORM框架.
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強大的地方還在于能夠簡化我們 對持久層業務邏輯的開發,通過規范持久層方法的名稱,通過名稱來判斷需要實現什么業務邏輯,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,對于一些復雜的,性能要求高的查詢,Spring Data JPA一樣支持我們使用原生的sql.
在這里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> |
我們引入這個依賴后,發現也引入了Hibernate的包,這是現在一種默認的做法,Hibernate已經被作為JPA規范的最好實現了,這里就不介紹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/jpaspring.datasource.druid.write.username=rootspring.datasource.druid.write.password=1spring.datasource.druid.write.driver-class-name=com.mysql.jdbc.Driverspring.datasource.druid.read.url=jdbc:mysql://localhost:3306/jpaspring.datasource.druid.read.username=rootspring.datasource.druid.read.password=1spring.datasource.druid.read.driver-class-name=com.mysql.jdbc.Driver#JPA (JpaBaseConfiguration, HibernateJpaAutoConfiguration)spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialectspring.jpa.database=mysqlspring.jpa.generate-ddl=true#就是hibernate.hbm2ddl.auto,具體說明可以看READMEspring.jpa.hibernate.ddl-auto=update#通過方法名解析sql的策略,具體說明可以看README,這里就不配置了spring.jpa.hibernate.naming-strategy=org.hibernate.cfg.DefaultComponentSafeNamingStrategyspring.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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@Configurationpublic 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") @Primary public DataSource writeDruidDataSource() { return new DruidDataSource(); }} |
EntityManagerFactory實例注入
EntityManagerFactory類似于Hibernate的SessionFactory,mybatis的SqlSessionFactory 總之,在執行操作之前,我們總要獲取一個EntityManager,這就類似于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于 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=updatespring.jpa.properties.hibernate.show_sql=truespring.jpa.properties.hibernate.use-new-id-generator-mappings=true@Configuration@EnableJpaRepositories(value = "com.lc.springBoot.jpa.repository", entityManagerFactoryRef = "writeEntityManagerFactory", transactionManagerRef="writeTransactionManager")public class WriteDataSourceConfig { @Autowired JpaProperties jpaProperties; @Autowired @Qualifier("writeDruidDataSource") private DataSource writeDruidDataSource; /** * EntityManagerFactory類似于Hibernate的SessionFactory,mybatis的SqlSessionFactory * 總之,在執行操作之前,我們總要獲取一個EntityManager,這就類似于Hibernate的Session, * mybatis的sqlSession. * @return */ @Bean(name = "writeEntityManagerFactory") @Primary public EntityManagerFactory writeEntityManagerFactory() { HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter(); LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean(); 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后,才初始化 return factory.getObject(); } /** * 配置事物管理器 * @return */ @Bean(name = "writeTransactionManager") @Primary public PlatformTransactionManager writeTransactionManager() { JpaTransactionManager jpaTransactionManager = new JpaTransactionManager(); jpaTransactionManager.setEntityManagerFactory(this.writeEntityManagerFactory()); return jpaTransactionManager; }} |
2.先注入LocalContainerEntityManagerFactoryBean,再獲取EntityManagerFactory
配置:
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spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialectspring.jpa.database=mysqlspring.jpa.generate-ddl=true#就是hibernate.hbm2ddl.auto,具體說明可以看READMEspring.jpa.hibernate.ddl-auto=update#通過方法名解析sql的策略,具體說明可以看README,這里就不配置了spring.jpa.hibernate.naming-strategy=org.hibernate.cfg.DefaultComponentSafeNamingStrategyspring.jpa.show-sql=true@Configuration@EnableJpaRepositories(value = "com.lc.springBoot.jpa.repository", entityManagerFactoryRef = "writeEntityManagerFactory", transactionManagerRef = "writeTransactionManager")public class WriteDataSourceConfig1 { @Autowired JpaProperties jpaProperties; @Autowired @Qualifier("writeDruidDataSource") private DataSource writeDruidDataSource; /** * 我們通過LocalContainerEntityManagerFactoryBean來獲取EntityManagerFactory實例 * @return */ @Bean(name = "writeEntityManagerFactoryBean") @Primary public LocalContainerEntityManagerFactoryBean writeEntityManagerFactoryBean(EntityManagerFactoryBuilder builder) { return builder .dataSource(writeDruidDataSource) .properties(jpaProperties.getProperties()) .packages("com.lc.springBoot.jpa.entity") //設置實體類所在位置 .persistenceUnit("writePersistenceUnit") .build(); //.getObject();//不要在這里直接獲取EntityManagerFactory } /** * EntityManagerFactory類似于Hibernate的SessionFactory,mybatis的SqlSessionFactory * 總之,在執行操作之前,我們總要獲取一個EntityManager,這就類似于Hibernate的Session, * mybatis的sqlSession. * @param builder * @return */ @Bean(name = "writeEntityManagerFactory") @Primary public EntityManagerFactory writeEntityManagerFactory(EntityManagerFactoryBuilder builder) { return this.writeEntityManagerFactoryBean(builder).getObject(); } /** * 配置事物管理器 * @return */ @Bean(name = "writeTransactionManager") @Primary public PlatformTransactionManager writeTransactionManager(EntityManagerFactoryBuilder builder) { return new JpaTransactionManager(writeEntityManagerFactory(builder)); }} |
對于這個配置
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@Bean(name = "writeEntityManagerFactoryBean") @Primary public LocalContainerEntityManagerFactoryBean writeEntityManagerFactoryBean(EntityManagerFactoryBuilder builder) { return builder .dataSource(writeDruidDataSource) .properties(jpaProperties.getProperties()) .packages("com.lc.springBoot.jpa.entity") //設置實體類所在位置 .persistenceUnit("writePersistenceUnit") .build(); //.getObject();//不要在這里直接獲取EntityManagerFactory } |
getObject()方法可以獲取到EntityManagerFactory的實例,看似跟第一種沒有什么區別,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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@Configurationpublic 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 */ @Bean public 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; }} |
自定義注解
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@Target({ElementType.METHOD, ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface TargetDataSource { String dataSource() default "";//數據源} |
使用ThreadLocal使數據源與線程綁定
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public class DynamicDataSourceHolder { //使用ThreadLocal把數據源與當前線程綁定 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 { @Override protected Object determineCurrentLookupKey() { //可以做一個簡單的負載均衡策略 String lookupKey = DynamicDataSourceHolder.getDataSource(); System.out.println("------------lookupKey---------"+lookupKey); return lookupKey; } } |
定義切面
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@Aspect @Component public 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("----------數據源是:" + targetDataSource + "------"); DynamicDataSourceHolder.setDataSource(targetDataSource); } Object result = pjp.proceed();//執行方法 DynamicDataSourceHolder.clearDataSource(); return result; } } |
以上所述是小編給大家介紹的SpringBoot集成Spring Data JPA及讀寫分離，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對服務器之家網站的支持！
