问题：

使用 @Transactional 注解后，多数据源切换失败

原因：

当我们配置了事物管理器和拦截Service中的方法后，每次执行Service中方法前会开启一个事务，并且同时会缓存一些东西：DataSource、SqlSessionFactory、Connection等，所以，我们在外面再怎么设置要求切换数据源也没用，因为Conneciton都是从缓存中拿的，所以我们要想能够顺利的切换数据源，实际就是能够动态的根据DatabaseType获取不同的Connection，并且要求不能影响整个事物的特性。也就是说springboot的声明式事务需要重写Transaction。

解决：新建两个类

MultiDataSourceTransaction.java类：

package com.ylz.bjyf.common.multipledatasource;

import groovy.util.logging.Slf4j;
import org.apache.ibatis.transaction.Transaction;

@Slf4j
public class MultiDataSourceTransaction implements Transaction {

    private final DataSource dataSource;

    private Connection mainConnection;

    private String mainDatabaseIdentification;

    private ConcurrentMap<String, Connection> otherConnectionMap;


    private boolean isConnectionTransactional;

    private boolean autoCommit;


    public MultiDataSourceTransaction(DataSource dataSource) {
        notNull(dataSource, "No DataSource specified");
        this.dataSource = dataSource;
        otherConnectionMap = new ConcurrentHashMap<>();
        mainDatabaseIdentification = DynamicDataSourceContextHolder.getMainDateSource();
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public Connection getConnection() throws SQLException {
        String databaseIdentification = DynamicDataSourceContextHolder.getDataSourceType();
        if (null == databaseIdentification || databaseIdentification.equals(mainDatabaseIdentification)) {
            if (mainConnection != null) {
                return mainConnection;
            } else {
                openMainConnection();
                mainDatabaseIdentification = databaseIdentification;
                return mainConnection;
            }
        } else {
            if (!otherConnectionMap.containsKey(databaseIdentification)) {
                try {
                    Connection conn = dataSource.getConnection();
                    otherConnectionMap.put(databaseIdentification, conn);
                } catch (SQLException ex) {
                    throw new CannotGetJdbcConnectionException("Could not get JDBC Connection", ex);
                }
            }
            return otherConnectionMap.get(databaseIdentification);
        }

    }


    private void openMainConnection() throws SQLException {
        this.mainConnection = DataSourceUtils.getConnection(this.dataSource);
        this.autoCommit = this.mainConnection.getAutoCommit();
        this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.mainConnection, this.dataSource);

        if (log.isDebugEnabled()) {
            log.debug(
                    "JDBC Connection ["
                            + this.mainConnection
                            + "] will"
                            + (this.isConnectionTransactional ? " " : " not ")
                            + "be managed by Spring");
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void commit() throws SQLException {
        if (this.mainConnection != null && !this.isConnectionTransactional && !this.autoCommit) {
            if (log.isDebugEnabled()) {
                log.debug("Committing JDBC Connection [" + this.mainConnection + "]");
            }
            this.mainConnection.commit();
            for (Connection connection : otherConnectionMap.values()) {
                connection.commit();
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void rollback() throws SQLException {
        if (this.mainConnection != null && !this.isConnectionTransactional && !this.autoCommit) {
            if (log.isDebugEnabled()) {
                log.debug("Rolling back JDBC Connection [" + this.mainConnection + "]");
            }
            this.mainConnection.rollback();
            for (Connection connection : otherConnectionMap.values()) {
                connection.rollback();
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void close() throws SQLException {
        DataSourceUtils.releaseConnection(this.mainConnection, this.dataSource);
        for (Connection connection : otherConnectionMap.values()) {
            DataSourceUtils.releaseConnection(connection, this.dataSource);
        }
    }

    @Override
    public Integer getTimeout() throws SQLException {
        return null;
    }
}

MultiDataSourceTransactionFactory类

public class MultiDataSourceTransactionFactory extends SpringManagedTransactionFactory {

    @Override
    public Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level,
                                      boolean autoCommit) {
        return new MultiDataSourceTransaction(dataSource);
    }
}

在mybatis-plus配置中添加配置：

@Configuration
public class MybatisPlusConfig {

    private String mapperLocations = "classpath*:mapper/**/*.xml";

    @Bean("sqlSessionFactory")
    @DependsOn({"dynamicDataSource"})
    @Primary
    public MybatisSqlSessionFactoryBean sqlSessionFactory(DataSource dynamicDataSource) {
        MybatisSqlSessionFactoryBean sessionFactoryBean = new MybatisSqlSessionFactoryBean();
        sessionFactoryBean.setDataSource(dynamicDataSource);
        sessionFactoryBean.setConfigLocation(new ClassPathResource("/mybatis/mybatis-config.xml"));
        sessionFactoryBean.setMapperLocations(ResourceUtil.getPathMatchingResource(mapperLocations));
        //事务配置
        sessionFactoryBean.setTransactionFactory(new MultiDataSourceTransactionFactory());
        return sessionFactoryBean;
    }
}

最后代码中引入：

@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Throwable.class)

需要注意的是：

在spring的文档中说道，spring声明式事务管理默认对非检查型异常和运行时异常进行事务回滚，而对检查型异常（try catch）则不进行回滚操作：
故而如果异常被try｛｝catch｛｝了，事务就不回滚了，如果想让事务回滚必须再往外抛try｛｝catch｛throw Exception｝。
启用事务后，主数据源 可以正常回滚，而 副数据源 无法回滚。原因是，项目的默认数据源是主数据源，在开启事务时，使用的是默认数据源，无论后面切换到哪个数据源，事务只有在主数据源上是开启的，事务回滚与提交也只操作主数据源。

参考链接：https://blog.csdn.net/gaoshili001/article/details/79378902
参考链接微信：https://mp.weixin.qq.com/s/PaLxmgH7R-aUOy2lOzZyFw