带你了解mybatis如何实现读写分离

1、spring aop实现

首先application-test.yml增加如下数据源的配置

spring:
 datasource:
   master:
     jdbc-url: jdbc:mysql://master域名:3306/test
     username: root
     password: 123456
     driver-class-name: com.mysql.jdbc.Driver
   slave1:
     jdbc-url: jdbc:mysql://slave域名:3306/test
     username: root   # 只读账户
     password: 123456
     driver-class-name: com.mysql.jdbc.Driver
   slave2:
     jdbc-url: jdbc:mysql://slave域名:3306/test
     username: root   # 只读账户
     password: 123456
     driver-class-name: com.mysql.jdbc.Driver

package com.cjs.example.enums;
public enum DBTypeEnum {
   MASTER, SLAVE1, SLAVE2;
}

定义ThreadLocal上下文，将当前线程的数据源进行动态修改

public class DBContextHolder {
   private static  volatile ThreadLocal<DBTypeEnum> contextHolder = new ThreadLocal<>();
   public static synchronized void set(DBTypeEnum dbType) {
       contextHolder.set(dbType);
   }
   public static synchronized DBTypeEnum get() {
       return contextHolder.get();
   }
   public static void master() {
       set(DBTypeEnum.MASTER);
   }
   public static void slave() {
       set(DBTypeEnum.SLAVE1);
   }
   public static void slave2(){ set(DBTypeEnum.SLAVE2); }
   // 清除数据源名
   public static void clearDB() {
       contextHolder.remove();
   }
}

重写mybatis数据源路由接口，在此修改数据源为我们上一块代码设置的上下文的数据源

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

将yml配置的多数据源手动指定注入

@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;
   }
}

sqlsession注入以上我们配置的datasource路由

@EnableTransactionManagement
@Configuration
@Import({TableSegInterceptor.class})
public class MyBatisConfig {
   @Resource(name = "myRoutingDataSource")
   private DataSource myRoutingDataSource;
   @Autowired
   private MybatisConfigProperty mybatisConfigProperty;
   @Autowired
   private TableSegInterceptor tableSegInterceptor;
   @Bean
   public SqlSessionFactory sqlSessionFactory() throws Exception {
       SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
       sqlSessionFactoryBean.setDataSource(myRoutingDataSource);
       // SpringBoot项目集成mybatis打包为jar运行时setTypeAliasesPackage无效解决
       VFS.addImplClass(SpringBootVFS.class);
       sqlSessionFactoryBean.setMapperLocations(
               new PathMatchingResourcePatternResolver().getResources(mybatisConfigProperty.getMapperLocations()));
       sqlSessionFactoryBean.setTypeAliasesPackage(mybatisConfigProperty.getTypeAliasesPackage());
       sqlSessionFactoryBean.setConfigLocation(
               new PathMatchingResourcePatternResolver().getResource(mybatisConfigProperty.getConfigLocation()));
       sqlSessionFactoryBean.setPlugins(new Interceptor[]{tableSegInterceptor});
       return sqlSessionFactoryBean.getObject();
   }
   @Bean
   public PlatformTransactionManager platformTransactionManager() {
       return new DataSourceTransactionManager(myRoutingDataSource);
   }
}

spring aop拦截指定前缀的service方法，并设置对应所属的上下文

@Aspect
@Component
public class DataSourceAop {
   @Pointcut("!@annotation(com.ask.student.interceptor.annotation.Master) " +
           "&& (execution(* com.ask.student.service..*.select*(..)) " +
           "|| execution(* com.ask.student.service..*.get*(..))" +
           "|| execution(* com.ask.student.service..*.find*(..))" +
           ")")
   public void readPointcut() {
   }
   @Pointcut("@annotation(com.ask.student.interceptor.annotation.Master) " +
           "|| execution(* com.ask.student.service..*.insert*(..)) " +
           "|| execution(* com.ask.student.service..*.clean*(..)) " +
           "|| execution(* com.ask.student.service..*.reset*(..)) " +
           "|| execution(* com.ask.student.service..*.add*(..)) " +
           "|| execution(* com.ask.student.service..*.update*(..)) " +
           "|| execution(* com.ask.student.service..*.edit*(..)) " +
           "|| execution(* com.ask.student.service..*.delete*(..)) " +
           "|| execution(* com.ask.student.service..*.remove*(..))")
   public void writePointcut() {
   }
   @Before("readPointcut()")
   public void read() {
       DBContextHolder.slave();
   }
   @Before("writePointcut()")
   public void write() {
       DBContextHolder.master();
   }
   @After("readPointcut()||writePointcut()")
   public void afterSwitchDS(){
       DBContextHolder.clearDB();
   }
}

以上最后一个方法的作用，在 * 中获取后及时清除避免导致来回切换当前线程变量延迟问题导致某些操作的数据源错误

DBContextHolder.clearDB();

@After("readPointcut()||writePointcut()")

public void afterSwitchDS(){

DBContextHolder.clearDB();

}

2、mybatis-plus的实现方式

这个方式配置简单，代码少，很多事情mybatis-plus都已经做好了，推荐使用

yml配置如下

 datasource:
   dynamic:
     primary: master  #设置默认的数据源或者数据源组,默认值即为master
     strict: false #设置严格模式,默认false不启动. 启动后在未匹配到指定数据源时候会抛出异常,不启动则使用默认数据源.
     datasource:
       master:
         url: jdbc:mysql://xxx:3306/db0?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&zeroDateTimeBehavior=convertToNull&serverTimezone=Asia/Shanghai
         username: admin
         password: 123456
         driver-class-name: com.mysql.cj.jdbc.Driver
         type: com.zaxxer.hikari.HikariDataSource
         hikari:
           minimum-idle: 5
           maximum-pool-size: 15
           auto-commit: true
           idle-timeout: 30000
           pool-name: springHikariCP
           max-lifetime: 1800000
           connection-timeout: 30000
           connection-test-query: SELECT 1
       slave1:
         url: jdbc:mysql://xxx:3306/db2?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&zeroDateTimeBehavior=convertToNull&serverTimezone=Asia/Shanghai
         username: admin
         password: 123456
         driver-class-name: com.mysql.cj.jdbc.Driver
         type: com.zaxxer.hikari.HikariDataSource
         hikari:
           minimum-idle: 5
           maximum-pool-size: 15
           auto-commit: true
           idle-timeout: 30000
           pool-name: springHikariCP
           max-lifetime: 1800000
           connection-timeout: 30000
           connection-test-query: SELECT 1
       slave2:
         url: jdbc:mysql://xxx:3306/db3?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&zeroDateTimeBehavior=convertToNull&serverTimezone=Asia/Shanghai
         username: admin
         password: 123456
         driver-class-name: com.mysql.cj.jdbc.Driver
         type: com.zaxxer.hikari.HikariDataSource
         hikari:
           minimum-idle: 5
           maximum-pool-size: 15
           auto-commit: true
           idle-timeout: 30000
           pool-name: springHikariCP
           max-lifetime: 1800000
           connection-timeout: 30000
           connection-test-query: SELECT 1

使用起来非常简单，只需要加上这个master的注解即可

   @Override
   @DS("master")
   public DestMedia getOneByCodeFromEpg(String code) {
       QueryWrapper queryWrapper = new QueryWrapper();
       queryWrapper.eq("code", code);
       return super.getOne(queryWrapper);
   }

来源：https://blog.csdn.net/u013309797/article/details/119254805