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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@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); } } |
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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@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; } } |
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) @Documented public @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 ) @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(); } } |
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
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