How SpringBoot implements dynamic switching of multiple data sources based on AbstractRoutingDataSource

1. Scenario

In the production business, some tasks perform long-time query operations. When the real-time requirements are not high, we hope to separate these query SQLs from Database queries to reduce application pressure on the main database.

One solution is to configure multiple data sources in the configuration file, and then obtain the data source and mapper-related scanning configuration through the configuration class. Different data sources configure different mapper scanning positions, and then which ones are needed A data source can be injected into any mapper interface. This method is relatively simple. The feature is to distinguish data sources through mapper scanning locations.

A feasible solution is to set a default data source in advance, define multiple other data sources at the same time, and use aop to implement annotations to switch data sources. Inheriting the AbstractRoutingDataSource class is the key to implementing this solution. This is the focus of this article.

2. Principle

The core logic of the dynamic switching of multiple data sources of AbstractRoutingDataSource is: when the program is running, the data source is dynamically woven into the program through AbstractRoutingDataSource, and the data is flexibly processed. Source switching.
Dynamic switching of multiple data sources based on AbstractRoutingDataSource can achieve separation of reading and writing. The logic is as follows:

/**
     * Retrieve the current target DataSource. Determines the
     * {@link #determineCurrentLookupKey() current lookup key}, performs
     * a lookup in the {@link #setTargetDataSources targetDataSources} map,
     * falls back to the specified
     * {@link #setDefaultTargetDataSource default target DataSource} if necessary.
     * @see #determineCurrentLookupKey()
     */
    protected DataSource determineTargetDataSource() {
        Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
        Object lookupKey = determineCurrentLookupKey();
        DataSource dataSource = this.resolvedDataSources.get(lookupKey);
        if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
            dataSource = this.resolvedDefaultDataSource;
        }
        if (dataSource == null) {
            throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
        }
        return dataSource;
    }
/**
     * Determine the current lookup key. This will typically be
     * implemented to check a thread-bound transaction context.
     * <p>Allows for arbitrary keys. The returned key needs
     * to match the stored lookup key type, as resolved by the
     * {@link #resolveSpecifiedLookupKey} method.
     */
    @Nullable
    protected abstract Object determineCurrentLookupKey();

Specify the data source that needs to be switched by implementing the abstract method determineCurrentLookupKey

3. Code example

The example mainly relies on

com.alibaba .druid;tk.mybatis

Define a class used to associate data sources. Use TheadLocal to save the flag (key) of which data source each thread selects

@Slf4j
public class DynamicDataSourceContextHolder {


    private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();
    public static List<String> dataSourceIds = new ArrayList<String>();

    public static void setDataSourceType(String dataSourceType) {
        log.info("设置当前数据源为{}",dataSourceType);
        contextHolder.set(dataSourceType);
    }

    public static String getDataSourceType() {
        return contextHolder.get() ;
    }

    public static void clearDataSourceType() {
        contextHolder.remove();
    }

    public static boolean containsDataSource(String dataSourceId){
        log.info("list = {},dataId={}", JSON.toJSON(dataSourceIds),dataSourceId);
        return dataSourceIds.contains(dataSourceId);
    }
}

Inheritance

AbstractRoutingDataSource

public class DynamicDataSource  extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {

        return  DynamicDataSourceContextHolder.getDataSourceType();
    }
}

Configure the main database master and slave database slave (omitted). The data source configuration can be simplified

@Configuration
@tk.mybatis.spring.annotation.MapperScan(value = {"com.server.dal.dao"})
@ConditionalOnProperty(name = "java.druid.datasource.master.url")
public class JavaDruidDataSourceConfiguration {

    private static final Logger logger = LoggerFactory.getLogger(JavaDruidDataSourceConfiguration.class);

    @Resource
    private JavaDruidDataSourceProperties druidDataSourceProperties;
    @Primary
    @Bean(name = "masterDataSource", initMethod = "init", destroyMethod = "close")
    @ConditionalOnMissingBean(name = "masterDataSource")
    public DruidDataSource javaReadDruidDataSource() {

        DruidDataSource result = new DruidDataSource();

        try {
//            result.setName(druidDataSourceProperties.getName());
            result.setUrl(druidDataSourceProperties.getUrl());
            result.setUsername(druidDataSourceProperties.getUsername());
            result.setPassword(druidDataSourceProperties.getPassword());
            result.setConnectionProperties(
                    "config.decrypt=false;config.decrypt.key=" + druidDataSourceProperties.getPwdPublicKey());
            result.setFilters("config");
            result.setMaxActive(druidDataSourceProperties.getMaxActive());
            result.setInitialSize(druidDataSourceProperties.getInitialSize());
            result.setMaxWait(druidDataSourceProperties.getMaxWait());
            result.setMinIdle(druidDataSourceProperties.getMinIdle());
            result.setTimeBetweenEvictionRunsMillis(druidDataSourceProperties.getTimeBetweenEvictionRunsMillis());
            result.setMinEvictableIdleTimeMillis(druidDataSourceProperties.getMinEvictableIdleTimeMillis());
            result.setValidationQuery(druidDataSourceProperties.getValidationQuery());
            result.setTestWhileIdle(druidDataSourceProperties.isTestWhileIdle());
            result.setTestOnBorrow(druidDataSourceProperties.isTestOnBorrow());
            result.setTestOnReturn(druidDataSourceProperties.isTestOnReturn());
            result.setPoolPreparedStatements(druidDataSourceProperties.isPoolPreparedStatements());
            result.setMaxOpenPreparedStatements(druidDataSourceProperties.getMaxOpenPreparedStatements());

            if (druidDataSourceProperties.isEnableMonitor()) {
                StatFilter filter = new StatFilter();
                filter.setLogSlowSql(druidDataSourceProperties.isLogSlowSql());
                filter.setMergeSql(druidDataSourceProperties.isMergeSql());
                filter.setSlowSqlMillis(druidDataSourceProperties.getSlowSqlMillis());
                List<Filter> list = new ArrayList<>();
                list.add(filter);
                result.setProxyFilters(list);
            }

        } catch (Exception e) {

            logger.error("数据源加载失败:", e);

        } finally {
            result.close();
        }


        return result;
    }
}

Pay attention to the bean name of the master-slave database

Configure DynamicDataSource

• targetDataSources stores the k-v pair of the data source

• defaultTargetDataSource stores the default data source

Configure the transaction manager and SqlSessionFactoryBean

@Configuration
public class DynamicDataSourceConfig {
    private static final String MAPPER_LOCATION = "classpath*:sqlmap/dao/*Mapper.xml";

    @Bean(name = "dynamicDataSource")
    public DynamicDataSource dynamicDataSource(@Qualifier("masterDataSource") DruidDataSource masterDataSource,
                                               @Qualifier("slaveDataSource") DruidDataSource slaveDataSource) {
        Map<Object, Object> targetDataSource = new HashMap<>();
        DynamicDataSourceContextHolder.dataSourceIds.add("masterDataSource");
        targetDataSource.put("masterDataSource", masterDataSource);
        DynamicDataSourceContextHolder.dataSourceIds.add("slaveDataSource");
        targetDataSource.put("slaveDataSource", slaveDataSource);
        DynamicDataSource dataSource = new DynamicDataSource();
        dataSource.setTargetDataSources(targetDataSource);
        dataSource.setDefaultTargetDataSource(masterDataSource);
        return dataSource;
    }

    @Primary
    @Bean(name = "javaTransactionManager")
    @ConditionalOnMissingBean(name = "javaTransactionManager")
    public DataSourceTransactionManager transactionManager(@Qualifier("dynamicDataSource") DynamicDataSource druidDataSource) {
        return new DataSourceTransactionManager(druidDataSource);
    }

    @Bean(name = "sqlSessionFactoryBean")
    public SqlSessionFactoryBean myGetSqlSessionFactory(@Qualifier("dynamicDataSource") DynamicDataSource  dataSource) {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        try {
            sqlSessionFactoryBean.setMapperLocations(resolver.getResources(MAPPER_LOCATION));
        } catch (IOException e) {
            e.printStackTrace();
        }
        sqlSessionFactoryBean.setDataSource(dataSource);
        return sqlSessionFactoryBean;
    }
}

Define an annotation to specify the data source

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface TargetDataSource {
    String value();
}

Aspect business logic. Pay attention to specifying order to ensure execution before starting the transaction.

@Aspect
@Slf4j
@Order(-1)
@Component
public class DataSourceAop {

    @Before("@annotation(targetDataSource)")
    public void changeDataSource(JoinPoint point, TargetDataSource targetDataSource) {
        String dsId = targetDataSource.value();
        if (!DynamicDataSourceContextHolder.containsDataSource(dsId)) {
            log.error("数据源[{}]不存在，使用默认数据源 > {}" + targetDataSource.value() + point.getSignature());
        } else {
            log.info("UseDataSource : {} > {}" + targetDataSource.value() + point.getSignature());
            DynamicDataSourceContextHolder.setDataSourceType(targetDataSource.value());

        }
    }

    @After("@annotation(targetDataSource)")
    public void restoreDataSource(JoinPoint point, TargetDataSource targetDataSource) {
        log.info("RevertDataSource : {} > {}"+targetDataSource.value()+point.getSignature());
        DynamicDataSourceContextHolder.clearDataSourceType();
    }
}

Pom.xml and application.yml are omitted above

Usage example

    @Resource
    private ShopBillDOMapper shopBillDOMapper;

//使用默认数据源
    public ShopBillBO queryTestData(Integer id){

        return shopBillDOMapper.getByShopBillId(id);
    }

//切换到指定的数据源
    @TargetDataSource("slaveDataSource")
    public ShopBill queryTestData2(Integer id){
        return shopBillDOMapper.getByShopBillId(id);
    }

If different results are returned, it will be successful!

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