Detailed explanation of examples of Spring Data JPA integration implemented by SpringBoot

This article mainly introduces the relevant knowledge of SpringBoot integrating Spring Data JPA and reading and writing separation. Friends in need can refer to the

related code: github OSCchina

What is JPA

JPA (Java Persistence API) is the Java persistence specification officially proposed by Sun, which provides a for Java developers Object/association mapping tool to manage relational data in Java applications. It includes the following aspects:

1. ORM mapping supports xml and annotation methods to create entities and tables Mapping between.

2. Java persistence API defines some commonly used CRUD interfaces, we only need to call them directly without considering the details of the underlying JDBC and SQL.

3.JPQLQuery Language This is a very important aspect in persistence operations. Query data through Object-oriented rather than database-oriented query language to avoid program SQL Statements are tightly coupled.

In our work, we all use ORM technologies, such as Hibernate, JOOQ, etc. Depending on the needs, we will use different ORMframeworks. When we need to change When the ORM framework meets our needs, we often need to reconstruct the code due to the implementation, usage, and differences of different ORM frameworks. The emergence of JPA is to solve this problem. JPA fully absorbs some of the existing The advantages of the ORM framework are that it is easy to use and has strong scalability. It provides a set of standard interfaces for ORM technology to integrate different ORM frameworks.

Hibernate's implementation of JPA

JPA itself does not implement specific implementations, but only defines some interface specifications, allowing otherORMs to implement these interfaces specifically. For now, The best implementation of the JPA specification is Hibernate. Let me mention Mybatis here. Mybatis does not implement the JPA specification, and it itself cannot be regarded as a real ORM framework.

Spring Data JPA What is

Spring Data JPA is just a module of the Spring Data framework, which can greatly simplify the use of JPA. The power of Spring Data JPA is that it can simplify our persistence layer business logic. By standardizing the names of persistence layer methods and using the names to determine what business logic needs to be implemented, we have the opportunity to complete most of our development without writing a sentence of SQL or doing any DAO layer logic. Of course, for For some complex queries with high performance requirements, Spring Data JPA also supports us to use native sql.

Here we will not introduce too much about JPA and Spring Data JPA, mainly some details of integration with SpringBoot and Example.

Introducing dependencies

<!-- 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>

After we introduced this dependency, we found that the Hibernate package was also introduced, which is now the default Practice, Hibernate has been regarded as the best implementation of the JPA specification. I will not introduce the configuration of the Druid data source here. You can read another article XXXX.

Configuring our data source And 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.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
#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 data source injection

@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")
  @Primary
  public DataSource writeDruidDataSource() {
    return new DruidDataSource();
  }
}

EntityManagerFactory instance injection

EntityManagerFactory is similar to Hibernate's SessionFactory and mybatis's SqlSessionFactory. In short, before performing an operation, we always need to obtain an EntityManager, which is similar to Hibernate's Session and mybatis's sqlSession. There are two ways to inject EntityManagerFactory, one is to directly inject EntityManagerFactory, The other is to inject indirectly through LocalContainerEntityManagerFactoryBean. Although both methods are based on LocalContainerEntityManagerFactoryBean, there are still some differences in configuration.

1. Directly inject EntityManagerFactory

Configuration: Configure Hibernate's properties through 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
@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")
  @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);//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")
  @Primary
  public PlatformTransactionManager writeTransactionManager() {
    JpaTransactionManager jpaTransactionManager = new JpaTransactionManager();
    jpaTransactionManager.setEntityManagerFactory(this.writeEntityManagerFactory());
    return jpaTransactionManager;
  }
}

2. First inject LocalContainerEntityManagerFactoryBean, and then obtain EntityManagerFactory

Configuration:

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 {
  @Autowired
  JpaProperties jpaProperties;
  @Autowired
  @Qualifier("writeDruidDataSource")
  private DataSource writeDruidDataSource;
  /**
   * 我们通过LocalContainerEntityManagerFactoryBean来获取EntityManagerFactory实例
   * @return
   */
  @Bean(name = "writeEntityManagerFactoryBean")
  @Primary
  public 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")
  @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));
  }
}

For this configuration

@Bean(name = "writeEntityManagerFactoryBean")
  @Primary
  public 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() method can get an instance of EntityManagerFactory, which seems to be no different from the first one, but we cannot use getObject() directly , otherwise it will not be obtained and a null pointer exception will be reported.

Read-write separation configuration

Custom injection 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
   */
  @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;
  }
}

Custom annotations

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

Use ThreadLocal to bind the data source to the thread

 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 {
    @Override
    protected 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;
    }
  }

Define aspects

@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("----------数据源是:" + targetDataSource + "------");
        DynamicDataSourceHolder.setDataSource(targetDataSource);
      }
      Object result = pjp.proceed();//执行方法
      DynamicDataSourceHolder.clearDataSource();
      return result;
    }
  }

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