Spring Boot（22）集成MyBatis Plus实现读写分离

Spring Boot（22）集成MyBatis Plus实现读写分离

前提

搭建mysql主从集群

方案

1. 拦截器自定义实现：侵入性较高
2. 中间件实现

方案一：拦截器自定义读写分离

思路：数据源抽象类AbstractRoutingDataSource#determineCurrentLookupKey，结合ThreadLocal，在切面根据CRUD决定数据源，然后mapper调用，对应数据源取决于上述determineCurrentLookupKey作为key对应的value（value就是一个DataSource）

规定：service，读接口以get或select作为前缀，写接口以add、insert、remove、delete、edit、update作为前缀

流程：

1. 定义切面：根据读写切点，决定AbstractRoutingDataSource#determineCurrentLookupKey返回值

   ThreadLocal

   // 读切点
   @Pointcut("execution(* com.xl.demo.mysql.service.*.select*(..)) " +
             "|| execution(* com.xl.demo.mysql.service.*.get*(..))")
   public void readPointcut() { }
   
   @Before("readPointcut()")
   public void read() {
       DbTypeContextHolder.slave();
   }
   
   // 写切点
   @Pointcut("execution(* com.xl.demo.mysql.service.*.insert*(..)) " +
             "|| execution(* com.xl.demo.mysql.service.*.add*(..)) " +
             "|| execution(* com.xl.demo.mysql.service.*.update*(..)) " +
             "|| execution(* com.xl.demo.mysql.service.*.edit*(..)) " +
             "|| execution(* com.xl.demo.mysql.service.*.delete*(..)) " +
             "|| execution(* com.xl.demo.mysql.service.*.remove*(..))")
   public void writePointcut() { }
   
   @Before("writePointcut()")
   public void write() {
       DbTypeContextHolder.master();
   }
   

2. 定义DbTypeContextHolder类：持有当前数据源的key

   接口：get、master、slave（slave按轮询选择一个）

   public enum DbTypeEnum {
       MASTER,
       SLAVE1,
       SLAVE2,
       ;
   }
   

   private static final ThreadLocal<DbTypeEnum> contextHolder = new ThreadLocal<>();
   
   public static DbTypeEnum get() {
       return contextHolder.get();
   }
   
   public static void master() {
       contextHolder.set(DbTypeEnum.MASTER)
   }
   
   private static final AtomicInteger counter = new AtomicInteger(-1);
   public static void slave() {
       int index = counter.getAndIncrement() % 2;
       if (counter.get() > 9999) {
           counter.set(-1);
       }
       
       if (index == 0) {
           contextHolder.set(DbTypeEnum.SLAVE1)
       } else {
           contextHolder.set(DbTypeEnum.SLAVE2)
       }
   }
   

   到目前，通过拦截器，基于不同的请求（读或写）切换数据源的key，然后AbstractRoutingDataSource#determineCurrentLookupKey根据这个key决定数据源

3. 实现AbstractRoutingDataSource抽象类，并注入到SqlSessionFactory

   1. 配置文件配置数据源

   2. 实现AbstractRoutingDataSource

      public class MyRoutingDataSource extends AbstractRoutingDataSource {
          @Nullable
          @Override
          protected Object determineCurrentLookupKey() {
              return DBContextHolder.get();
          }
      }
      

   3. 数据源Bean配置

      @Configuration
      public class DataSourceConfig {
      
          @Bean
          @ConfigurationProperties("spring.datasource.master")
          public DataSource masterDataSource() {
              return DataSourceBuilder.create().build();
          }
      
          @Bean
          @ConfigurationProperties("spring.datasource.slave1")
          public DataSource slave1DataSource() {
              return DataSourceBuilder.create().build();
          }
      
          @Bean
          public DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                                @Qualifier("slave1DataSource") DataSource slave1DataSource) {
              Map<Object, Object> targetDataSources = new HashMap<>();
              targetDataSources.put(DbTypeEnum.MASTER, masterDataSource);
              targetDataSources.put(DbTypeEnum.SLAVE1, slave1DataSource);
      
              MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();
              myRoutingDataSource.setDefaultTargetDataSource(masterDataSource);
              myRoutingDataSource.setTargetDataSources(targetDataSources);
              return myRoutingDataSource;
          }
      
      }
      

   4. SqlSessionFactory注入数据源

      @Configuration
      public class MyBatisConfig {
      
          @Resource(name = "myRoutingDataSource")
          private DataSource myRoutingDataSource;
      
          @Bean
          public SqlSessionFactory sqlSessionFactory() throws Exception {
              MybatisSqlSessionFactoryBean factoryBean = new MybatisSqlSessionFactoryBean();
              factoryBean.setDataSource(myRoutingDataSource);
              return factoryBean.getObject();
          }
      
      }
      

补充：存在一些场景，刚写就需要查询，所以新增注解@Master，在切面中，写切点加入该注解，读切点去除该注解

方案二：中间件

proxy：mycat

步骤：

1. 安装mycat并配置读写分离
2. Spring Boot的数据源改为mycat

client：shardingsphere

步骤：

1. 添加依赖
2. 配置

refer：

SpringBoot结合ShardingSphere实现主从读写分离