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：
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;
}
@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)
@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
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
@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
@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
@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 。
@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
@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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