引入mybatis-plus相关包，pom.xml文件

配置文件application.property增加多库配置

mysql 数据源配置

spring.datasource.primary.jdbc-url=jdbc:mysql://xx.xx.xx.xx:3306/portal?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC&characterEncoding=utf8&serverTimezone=GMT%2B8
spring.datasource.primary.username=root
spring.datasource.primary.password=root
spring.datasource.primary.driver-class-name=com.mysql.cj.jdbc.Driver
#mysql slave 数据源配置

spring.datasource.slave.jdbc-url=jdbc:mysql://xx.xx.xx.xx:3306/portal?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC&characterEncoding=utf8&serverTimezone=GMT%2B8
spring.datasource.slave.username=root
spring.datasource.slave.password=root
spring.datasource.slave.driver-class-name=com.mysql.cj.jdbc.Driver

配置数据源及注解

数据源配置 MultiDataSourceConfig.Java

@Profile("dev")//开发模式配置文件
@Configuration
@MapperScan(basePackages = "com.csc.portal.mapper")//扫描包
public class MultiDataSourceConfig {

  
  @Bean
  @ConfigurationProperties(prefix = "spring.datasource.primary")
  public DataSource masterDataSource() {
    return DataSourceBuilder.create().build();
  }

  
  @Bean
  @ConfigurationProperties(prefix = "spring.datasource.slave")
  public DataSource slaveDataSource() {
    return DataSourceBuilder.create().build();
  }

  
  @Bean
  public DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                     @Qualifier("slaveDataSource") DataSource slaveDataSource) {
    Map<Object, Object> targetDataSources = new HashMap<>();
    targetDataSources.put(DBTypeEnum.MASTER, masterDataSource);
    targetDataSources.put(DBTypeEnum.SLAVE, slaveDataSource);
    MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();
    myRoutingDataSource.setDefaultTargetDataSource(slaveDataSource);//设置默认数据源
    myRoutingDataSource.setTargetDataSources(targetDataSources);//设置路由表，使用map的key，value方式得到对应数据源
    return myRoutingDataSource;
  }

数据库枚举类

public enum DBTypeEnum {
 MASTER, SLAVE;
}

注解

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Master {
}

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Slave {
}

Mybatis-plus配置

@EnableTransactionManagement
@Configuration
@MapperScan(basePackages = "com.csc.portal.mapper")
public class MybatisPlusConfig {
  
  @Bean
  public PaginationInterceptor paginationInterceptor() {
    return new PaginationInterceptor();
  }

  @Resource(name = "myRoutingDataSource")
  private DataSource myRoutingDataSource;
  
  @Bean
  public SqlSessionFactory sqlSessionFactory() throws Exception {
    MybatisSqlSessionFactoryBean sqlSessionFactoryBean = new MybatisSqlSessionFactoryBean();
    sqlSessionFactoryBean.setDataSource(myRoutingDataSource);
    sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper
  

  
  @Bean
  public DataSourceTransactionManager transactionManager() {
    DataSourceTransactionManager tx = new DataSourceTransactionManager();
    tx.setDataSource(myRoutingDataSource);
    return tx;
  }

增加数据源管理类

DBContextHolder.java

public class DBContextHolder {

  
  private static final ThreadLocal<DBTypeEnum> contextHolder = new ThreadLocal<>();

  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() {
    set(DBTypeEnum.SLAVE);
    System.out.println("切换到slave");
  }

}

指定选择数据源

MyRoutingDataSource.java 方法determineCurrentLookupKey决定最终使用哪个数据源进行操作，若为空则使用默认数据源。

public class MyRoutingDataSource extends AbstractRoutingDataSource {
  @Nullable
  @Override
  protected Object determineCurrentLookupKey() {
    System.out.println("线程名："+Thread.currentThread().getName()+":"+DBContextHolder.get());
    return DBContextHolder.get();

    //return DBContextHolder.get();
  }

}

增加aop切面

@Aspect
@Component
@Order(0)//配置注解优先级，优于事物注解@Transactional先进行数据源切换，
//不然在事物中进行数据源切换无效
public class DataSourceAop {

  @Pointcut(
      " @annotation(com.csc.portal.annotation.Slave)")
  public void readPointcut() {

  }


  @Pointcut("@annotation(com.csc.portal.annotation.Master) " //+
     )
  public void writePointcut() {

  }

  @Before("readPointcut()")
  public void read() {
    //获取拦截类
    DBContextHolder.slave();
    System.out.println(Thread.currentThread().getName()+DBContextHolder.get());
  }

  @Before("writePointcut()")
  public void write() {
    //获取拦截类

    DBContextHolder.master();
    System.out.println(Thread.currentThread().getName()+DBContextHolder.get());
  }  
}

实际应用

1. 在service层方法前增加注解@Master表示使用主库，进行增删改的操作使用主库。
2. 在service层方法前增加注解@Slave表示使用从库，进行查的操作使用从库，默认使用从库，可不配置。
3. @ Transactional注解加到service层，增加了@Transactional注解后，启用事务后，一个事务内部的connection是复用的，所以就算AOP切了数据源字符串，但是数据源并不会被真正修改。所以@Transactional注解不要写在controller层，不然在service层也切换不了数据源。
4. @Transactional与@Master可同时使用，已经配置@Master注解的优先级较高，先切换数据源后执行事务。
   

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