spring aop实现数据库读写分离

1、应用层解决：
（1）导入spring-boot-starter-aop包；

<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-aop</artifactId>
</dependency>

（2）配置datasource.yml文件，配置主从库的驱动、账号、密码、url等,datasource.yml:

spring:
  datasource:
    master:
      jdbc-url: jdbc:mysql://47.99.221.117:3306/lefeng
      username: root  #主库
      password: 1+1j1804
      driver-class-name: com.mysql.cj.jdbc.Driver
    slave1:
      jdbc-url: jdbc:mysql://47.110.60.167:3306/lefeng
      username: root   # 从库
      password: 1+1j1804
      driver-class-name: com.mysql.cj.jdbc.Driver
    slave2:
      jdbc-url: jdbc:mysql://47.110.60.167:3306/lefeng
      username: root   # 从库
      password: 1+1j1804
      driver-class-name: com.mysql.cj.jdbc.Driver

（3）设置DataSourceConfig，将主从数据库注入DataSource中；

@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
    @ConfigurationProperties("spring.datasource.slave2")
    public DataSource slave2DataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean
    public DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                          @Qualifier("slave1DataSource") DataSource slave1DataSource,
                                          @Qualifier("slave2DataSource") DataSource slave2DataSource) {
        Map<Object, Object> targetDataSources = new HashMap<>();
        targetDataSources.put(DBTypeEnum.MASTER, masterDataSource);
        targetDataSources.put(DBTypeEnum.SLAVE1, slave1DataSource);
        targetDataSources.put(DBTypeEnum.SLAVE2, slave2DataSource);
        MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();
        myRoutingDataSource.setDefaultTargetDataSource(masterDataSource);
        myRoutingDataSource.setTargetDataSources(targetDataSources);
        return myRoutingDataSource;
    }
}

（4）定义切面，不同的操作切换成不同的数据源；

@Aspect
@Component
public class DataSourceAop {
        @Before("execution(* com.lefeng.lf_front.dao.*.*(..))")
    public void before(JoinPoint jp) {
        String methodName = jp.getSignature().getName();

        if (StringUtils.startsWithAny(methodName, "get", "select", "find")) {
            DBContextHolder.slave();
        }else {
            DBContextHolder.master();
        }
    }
}

（5）通过MyRoutingDataSource获取当前采用的数据源；

public class MyRoutingDataSource extends AbstractRoutingDataSource {

    @Nullable
    @Override
    protected Object determineCurrentLookupKey() {
        return DBContextHolder.get();
    }
}

（6）通过ThreadLocal保存当前操作的数据源；

public class DBContextHolder {
    private static final ThreadLocal<DBTypeEnum> contextHolder = new ThreadLocal<>();

    private static final AtomicInteger counter = new AtomicInteger(-1);

    public static void set(DBTypeEnum dbType) {
        contextHolder.set(dbType);
    }

    public static DBTypeEnum get() {
        return contextHolder.get();
    }

    public static void master() {
        set(DBTypeEnum.MASTER);
        System.out.println("切换到master");
    }

    public static void slave() {
        //  轮询
        int index = counter.getAndIncrement() % 2;
        if (counter.get() > 9999) {
            counter.set(-1);
        }
        if (index == 0) {
            set(DBTypeEnum.SLAVE1);
            System.out.println("切换到slave1");
        }else {
            set(DBTypeEnum.SLAVE2);
            System.out.println("切换到slave2");
        }
    }

}

（7）将MyRoutingDataSource注入到MyBatis配置文件中；

@EnableTransactionManagement
@Configuration
public class MyBatisConfig {
    @Resource(name = "myRoutingDataSource")
    private DataSource myRoutingDataSource;

    @Bean
    public SqlSessionFactory sqlSessionFactory() throws Exception {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(myRoutingDataSource);
        sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));
        return sqlSessionFactoryBean.getObject();
    }

    @Bean
    public PlatformTransactionManager platformTransactionManager() {
        return new DataSourceTransactionManager(myRoutingDataSource);
    }
}

（8）需要设置数据集的主从复制，即在主库中开放一个只读权限的账号，用于在从库中启动主从复制。