springboot-mybatis多数据源

多数据源的目的

• 随着业务的发展，单库的的形式已经无法承受高并发所带来的压力，一个项目使用多个数据库显得额外重要，比如读写分离、主从复制

mybatis配置多数据源的方式

分包的方式

• 将不同数据源的mapper文件分开
• 读数据源

  @Configuration
  @MapperScan(basePackages="com.yechuan.dao.read",sqlSessionFactoryRef="readSqlSessionFactory")
  public class ReadDataSourceConfig {
	@Primary
	@Bean(name = "readDataSource")
	@ConfigurationProperties("datasources.read")
		public DataSource readDataSource() {
		return new DruidDataSource();
	}

	@Primary
	@Bean(name = "readDataSourceTransactionManager")
	public DataSourceTransactionManager dataSourceTransactionManager(DataSource dataSource) {
	    return new DataSourceTransactionManager(dataSource);
	}

	@Primary
	@Bean(name = "readSqlSessionFactory")
	public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
	    SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
	    sqlSessionFactoryBean.setDataSource(dataSource);
	    return sqlSessionFactoryBean.getObject();
	}

	@Primary
	@Bean(name = "readSqlSessionTemplate")
	public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
	    return new SqlSessionTemplate(sqlSessionFactory);
	}

   }

• 写数据源

@Configuration
@MapperScan(basePackages = "com.yechuan.dao.write", sqlSessionFactoryRef = "writeSqlSessionFactory")
public class WriteDataSourceConfig {

    @Bean(name = "writeDataSource")
    @ConfigurationProperties("datasources.write")
    public DataSource writeDataSource() {
        return new DruidDataSource();

    }

    @Bean(name = "writeDataSourceTransactionManager")
    public DataSourceTransactionManager dataSourceTransactionManager(@Qualifier("writeDataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }

    @Bean(name = "writeSqlSessionFactory")
    public SqlSessionFactory sqlSessionFactory(@Qualifier("writeDataSource") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(dataSource);
        return sqlSessionFactoryBean.getObject();
    }

    @Bean(name = "writeSqlSessionTemplate")
    public SqlSessionTemplate sqlSessionTemplate(@Qualifier("writeSqlSessionFactory") SqlSessionFactory sqlSessionFactory) {
        return new SqlSessionTemplate(sqlSessionFactory);
    }
}

AOP

• 利用aop原理，在访问数据库之前，替换数据库实例
• 在访问数据库的时候，会访问AbstractRoutingDataSource的determineCurrentLookupKey方法来获取数据库的实例key

1. 定义一个枚举类来说明一下当前数据源实例key有哪些

   public enum DataSourceKey {
   	READ("read"),
   	WRITE("write");
   
   	private String name;
   
   	public String getName() {
   		return name;
   	}
   
   	public void setName(String name) {
   		this.name = name;
   	}
   
   	private DataSourceKey(String name) {
   		this.name = name;
   	}
   }
   

2. 创建一个工具类来实现，存储与获取数据源key

   public class DynamicDataSourceContextHolder {
   	/**
   	*
   	* 保证其线程安全
   	*/
   	private static ThreadLocal<Object> CONTEXT_HOLDER = ThreadLocal.withInitial(() -> DataSourceKey.READ.getName());
   	/**
   	*
   	* 存储
   	*/
   	public static void setDataSourceKey(String key){
   		CONTEXT_HOLDER.set(key);
   	}
   	/**
   	*
   	* 获取
   	*/
   	public static Object getDataSourceKey(){
   		return CONTEXT_HOLDER.get();
   	}
   	/**
   	*
   	* 删除
   	*/
   	public static void clearDataSourceKey(){
   		CONTEXT_HOLDER.remove();
   	}
   
   }
   

3. 重写AbstractRoutingDataSource

   @Slf4j
   public class DynamicRoutingDataSource extends AbstractRoutingDataSource {
   
   	@Override
   	protected Object determineCurrentLookupKey() {
   		log.info("当前使用的数据源是 : {}",DynamicDataSourceContextHolder.getDataSourceKey());
   		return DynamicDataSourceContextHolder.getDataSourceKey();
   	}
   
   }
   

4. 配置数据源

   @Configuration
   public class DataSourceConfig {
     @Primary
     @Bean(name = "readDataSource")
     @ConfigurationProperties("datasources.read")
     public DataSource readDataSource() {
         return new DruidDataSource();
     }
   
     @Bean(name = "writeDataSource")
     @ConfigurationProperties("datasources.write")
     public DataSource writeDataSource() {
           return new DruidDataSource();
   
     }
     @Bean(name = "dynamicDataSource")
     public DataSource dynamicDataSource(@Qualifier(value = "readDataSource")DataSource readDataSource,@Qualifier(value = "writeDataSource")DataSource writeDataSource){
       	DynamicRoutingDataSource dynamicRoutingDataSource = new DynamicRoutingDataSource();
   
       	Map<Object, Object> dataSourceMap = new HashMap<Object, Object>(2);
       	dataSourceMap.put(DataSourceKey.READ.getName(),readDataSource);
       	dataSourceMap.put(DataSourceKey.WRITE.getName(),writeDataSource);
   
       	dynamicRoutingDataSource.setDefaultTargetDataSource(readDataSource);
       	dynamicRoutingDataSource.setTargetDataSources(dataSourceMap);
   
       	DynamicDataSourceContextHolder.dataSourceKeys.addAll(dataSourceMap.keySet());
   
       	return dynamicRoutingDataSource;
     }
   
     @Bean
     public DataSourceTransactionManager dataSourceTransactionManager(@Qualifier(value = "dynamicDataSource") DataSource dataSource) {
         return new DataSourceTransactionManager(dataSource);
     }
   
     @Bean
     public SqlSessionFactory sqlSessionFactory(@Qualifier(value = "dynamicDataSource") DataSource dataSource) throws Exception {
         SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
         sqlSessionFactoryBean.setDataSource(dataSource);
         return sqlSessionFactoryBean.getObject();
     }
   
     @Bean
     public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
         return new SqlSessionTemplate(sqlSessionFactory);
     }
   }
   

5. 自定义注解

   
   @Target({ElementType.METHOD, ElementType.TYPE})
   @Retention(RetentionPolicy.RUNTIME)
   @Documented
   public @interface UserDataSource {
   	DataSourceKey value() default DataSourceKey.READ;
   }
   

6. AOP动态切换数据源

   @Slf4j
   @Aspect
   @Component
   public class DynamicDataSourceAspect {
   
   
   	@Before("@annotation(userDataSource))")
   	public void switchDataSource(JoinPoint joinPoint,UserDataSource userDataSource){
   	DynamicDataSourceContextHolder.setDataSourceKey(targetDataSource.value().getName());
           log.info("在方法 ：[{}] 内切换数据源为： [{}]",
           joinPoint.getSignature(),DynamicDataSourceContextHolder.getDataSourceKey());
   
   	}
   
   	@After("@annotation(userDataSource))")
   	public void restoreDataSource(JoinPoint joinPoint,UserDataSource userDataSource){
           DynamicDataSourceContextHolder.clearDataSourceKey();
           log.info("在方法 [{}] 执行后，恢复数据源 [{}]",
              joinPoint.getSignature(),DynamicDataSourceContextHolder.getDataSourceKey());
   	}
   
   }
   

7. 在调用的时候使用注解即可

使用mybatis-puls与dynamic

• 鲁迅先生曾经说过我们不要自己造轮子，要使用别人的轮子

1. 导入相关依赖

   <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
        <version>2.5.4</version>
   </dependency>
   <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.3.1.tmp</version>
   </dependency>
   

2. yml配置

   spring:
     datasource:
       dynamic:
         datasource:
           read:
             password: root
             username: root
             url: jdbc:mysql://localhost:3306/sharding_sphere_read
             driverClassName: com.mysql.jdbc.Driver
           write:
             password: root
             username: root
             url: jdbc:mysql://localhost:3306/sharding_sphere_write
             driverClassName: com.mysql.jdbc.Driver
         primary: read
         strict: true
   

3. 使用

       @DS("write")
       @Transactional(rollbackFor = Exception.class)
       public void addUser( UserDto userDto) {
           userDao.insert(userDto);
       }