一、场景
在生产业务中，有一些任务执行了耗时较长的查询操作，在实时性要求不高的时候，我们希望将这些查询sql分离出来，去从库查询，以减少应用对主数据库的压力。
一种方案是在配置文件中配置多个数据源，然后通过配置类来获取数据源以及mapper相关的扫描配置，不同的数据源配置不佟的mapper扫描位置，然后需要哪一个数据源就注入哪一个mapper接口即可，这种方法比较简单。特征是通过mapper扫描位置区分数据源。
第二种方案是配置一个默认使用的数据源，然后定义多个其他的数据源，使用aop形成注解式选择数据源。此种方案实现的核心是对AbstractRoutingDataSource 类的继承。这是本文的重点。
二、原理
AbstractRoutingDataSource的多数据源动态切换的核心逻辑是：在程序运行时，把数据源数据源通过 AbstractRoutingDataSource 动态织入到程序中，灵活的进行数据源切换。
基于AbstractRoutingDataSource的多数据源动态切换，可以实现读写分离。逻辑如下：
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/** * 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(); |
通过实现抽象方法determineCurrentLookupKey指定需要切换的数据源
三、代码示例
示例中主要依赖
com.alibaba.druid;tk.mybatis
定义一个类用于关联数据源。通过 TheadLocal 来保存每个线程选择哪个数据源的标志(key)
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@Slf4jpublic 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); }} |
继承
AbstractRoutingDataSource
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public class DynamicDataSource extends AbstractRoutingDataSource { @Override protected Object determineCurrentLookupKey() { return DynamicDataSourceContextHolder.getDataSourceType(); }} |
配置主数据库master 与从数据库slave（略）。数据源配置可以从简
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@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; }} |
注意主从数据库的bean name
配置DynamicDataSource
- targetDataSources 存放数据源的k-v对
- defaultTargetDataSource 存放默认数据源
配置事务管理器和SqlSessionFactoryBean
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@Configurationpublic 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; }} |
定义一个注解用于指定数据源
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@Target({ ElementType.METHOD, ElementType.TYPE })@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface TargetDataSource { String value();} |
切面的业务逻辑。注意指定order，以确保在开启事务之前执行 。
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@Aspect@Slf4j@Order(-1)@Componentpublic 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(); }} |
以上略去了pom.xml和application.yml
使用示例
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@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); } |
如果返回不同的结果就成功了！
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原文链接：https://blog.csdn.net/long710910256/article/details/124945630
