springboot-jpa实现多数据源，读写分离

在项目中，多数据源的配置还是用的比较多的，现在就来介绍下springboot整合jpa实现多数据源配置
1.导入maven依赖:

     
      
            org.springframework.boot
            spring-boot-starter-data-jpa
        
         
         
            mysql
            mysql-connector-java
            8.0.11
        

2.application.yml配置:

spring:
  jackson:
    date-format: yyyy-MM-dd HH:mm:ss.SSS
    time-zone: GMT+8
  datasource:
    primary:  ###primary配置
       url: jdbc:mysql://localhost:3306/seller?user=root&password=mysql0000&useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=GMT%2B8
    backup: ####backup配置
       url: jdbc:mysql://localhost:3306/backupseller?user=root&password=mysql0000&useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=GMT%2B8
    driver-class-name: com.mysql.jdbc.Driver

3.数据源配置，包括DataSource配置，entityManagerFactory，以及transactionManager的配置,详见代码:

@Configuration
public class DataSourceAccessConfiguration {

    @Autowired
    private JpaProperties jpaProperties;

    @Autowired
    private ObjectProvider> providers;
    @Autowired
    private ObjectProvider physicalNamingStrategy;
    @Autowired
    private ObjectProvider implicitNamingStrategy;

    /**
     * 主数据库连接配置
     * @return
     */
    @Bean
    @Qualifier("primaryDataSource")
    @ConfigurationProperties("spring.datasource.primary")
    @Primary
    public DataSource primaryDataSource(){
        return DataSourceBuilder.create().build();
    }

    /**
     * 备数据库连接配置
     * @return
     */
    @Qualifier("backupDataSource")
    @Bean
    @ConfigurationProperties("spring.datasource.backup")
    public DataSource backupDataSource(){
        return DataSourceBuilder.create().build();
    }

    /**
     * 主 EntityManagerFactory配置
     * @param builder
     * @return
     */
    @Bean
    @Qualifier("primaryEntityManagerFactory")
    @Primary
    public LocalContainerEntityManagerFactoryBean primaryEntityManagerFactory(EntityManagerFactoryBuilder builder){
        return builder.dataSource(primaryDataSource())
                .properties(getVendorProperties(primaryDataSource()))
                .packages(OrderRepository.class) //扫描OrderRepository所在的包
                .persistenceUnit("primary")
                .build();

    }

    /**
     * 主 TransactionManager配置 事务配置
     * @param builder
     * @return
     */
    @Bean
    @Qualifier("primaryTransactionManager")
    @Primary
    public PlatformTransactionManager primaryTransactionManager(@Qualifier("primaryEntityManagerFactory") LocalContainerEntityManagerFactoryBean primaryEntityManagerFactory) {
        JpaTransactionManager transactionManager = new JpaTransactionManager(primaryEntityManagerFactory.getObject());
        return transactionManager;
    }

    /**
     * 备 EntityManagerFactory配置
     * @param builder
     * @return
     */
    @Bean
    @Qualifier("backupEntityManagerFactory")
    public LocalContainerEntityManagerFactoryBean backupEntityManagerFactory(EntityManagerFactoryBuilder builder){
        return builder.dataSource(backupDataSource())
                      .properties(getVendorProperties(backupDataSource()))
                      .packages(VerifyOrderRepository.class)  //扫描VerifyOrderRepository所在的包
                      .persistenceUnit("backup")
                      .build();

    }

    /**
     * 备 TransactionManager配置 事务配置
     * @param builder
     * @return
     */
    @Bean
    @Qualifier("backupTransactionManager")
    public PlatformTransactionManager backupTransactionManager(@Qualifier("backupEntityManagerFactory") LocalContainerEntityManagerFactoryBean backupEntityManagerFactory) {
        JpaTransactionManager transactionManager = new JpaTransactionManager(backupEntityManagerFactory.getObject());
        return transactionManager;
    }


    /**
     * 配置hibernate的配置信息
     * @param dataSource
     * @return
     */
    protected Map getVendorProperties(DataSource dataSource) {
        Map vendorProperties = new LinkedHashMap();
        String defaultDdlMode = new  HibernateDefaultDdlAutoProvider(
                providers.getIfAvailable(Collections::emptyList))
                .getDefaultDdlAuto(dataSource);
        vendorProperties.putAll(jpaProperties.getHibernateProperties(
                new HibernateSettings().ddlAuto(defaultDdlMode).physicalNamingStrategy(physicalNamingStrategy.getIfAvailable())
                        .implicitNamingStrategy(implicitNamingStrategy.getIfAvailable())
        ));
        return vendorProperties;
    }

    class HibernateDefaultDdlAutoProvider implements SchemaManagementProvider {
        private final List providers;

        HibernateDefaultDdlAutoProvider(List providers) {
            this.providers = providers;
        }

        public String getDefaultDdlAuto(DataSource dataSource) {
            if (!EmbeddedDatabaseConnection.isEmbedded(dataSource)) {
                return "none";
            } else {
                SchemaManagement schemaManagement = this.getSchemaManagement(dataSource);
                return SchemaManagement.MANAGED.equals(schemaManagement) ? "none" : "create-drop";
            }
        }

        public SchemaManagement getSchemaManagement(DataSource dataSource) {
            Iterator var2 = this.providers.iterator();

            SchemaManagement schemaManagement;
            do {
                if (!var2.hasNext()) {
                    return SchemaManagement.UNMANAGED;
                }

                SchemaManagementProvider provider = (SchemaManagementProvider)var2.next();
                schemaManagement = provider.getSchemaManagement(dataSource);
            } while(!SchemaManagement.MANAGED.equals(schemaManagement));

            return schemaManagement;
        }
    }
}

repository的目录结构如下:

基于上面的基本配置，即可完成多数据源的配置。。。。

另: 实现读写分离，只需要在别的数据源下创建接口，实现主数据库的repository接口，即可实现读写分离，这也是最简单的方式。

上述接口BackUpOrderRepository实现主库的OrderRepository接口，但是却在从库的包下，这样，具备主库的功能，但是却操作的是从库，这样就可以实现读写分离，至于数据数主库，从库数据一致性问题，这里不做讨论，mycat，otter可以解决这些问题，感兴趣的可以去看看，这里就不做详细的介绍了。

至此，springBoot整合jpa多数据源，读写分离，就介绍完毕了。。。