今天小编给大家分享一下mybatisplus @DS怎么实现动态切换数据源的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。
1、mybatis-plus @DS实现动态切换数据源原理
首先mybatis-plus使用com.baomidou.dynamic.datasource.AbstractRoutingDataSource继承 AbstractDataSource接管数据源；具体实现类为com.baomidou.dynamic.datasource.DynamicRoutingDataSource。项目初始化调用public synchronized void addDataSource(String ds, DataSource dataSource)加载数据源，数据源存进dataSourceMap中。
private Map<String, DataSource> dataSourceMap = new LinkedHashMap<>();
private Map<String, DynamicGroupDataSource> groupDataSources = new ConcurrentHashMap<>();public synchronized void addDataSource(String ds, DataSource dataSource) { if (p6spy) { dataSource = new P6DataSource(dataSource); } dataSourceMap.put(ds, dataSource); if (ds.contains(UNDERLINE)) { String group = ds.split(UNDERLINE)[0]; if (groupDataSources.containsKey(group)) { groupDataSources.get(group).addDatasource(dataSource); } else { try { DynamicGroupDataSource groupDatasource = new DynamicGroupDataSource(group, strategy.newInstance()); groupDatasource.addDatasource(dataSource); groupDataSources.put(group, groupDatasource); } catch (Exception e) { log.error("dynamic-datasource - add the datasource named [{}] error", ds, e); dataSourceMap.remove(ds); } } } log.info("dynamic-datasource - load a datasource named [{}] success", ds); }进行数据操作时，方法会被com.baomidou.dynamic.datasource.aop.DynamicDataSourceAnnotationInterceptor拦截，
public class DynamicDataSourceAnnotationInterceptor implements MethodInterceptor { private static final String DYNAMIC_PREFIX = "#"; private static final DynamicDataSourceClassResolver RESOLVER = new DynamicDataSourceClassResolver(); @Setter private DsProcessor dsProcessor; @Override public Object invoke(MethodInvocation invocation) throws Throwable { try { DynamicDataSourceContextHolder.push(determineDatasource(invocation)); return invocation.proceed(); } finally { DynamicDataSourceContextHolder.poll(); } } private String determineDatasource(MethodInvocation invocation) throws Throwable { Method method = invocation.getMethod(); DS ds = method.isAnnotationPresent(DS.class) ? method.getAnnotation(DS.class) : AnnotationUtils.findAnnotation(RESOLVER.targetClass(invocation), DS.class); String key = ds.value(); return (!key.isEmpty() && key.startsWith(DYNAMIC_PREFIX)) ? dsProcessor .determineDatasource(invocation, key) : key; }}拦截器首先从被拦截的方法或者类（一般@DS注解用于Service，也可用于Mapper和Controller）上寻找@DS注解，获取到@DS注解的值后将其存入com.baomidou.dynamic.datasource.toolkit.DynamicDataSourceContextHolder；DynamicDataSourceContextHolder使用ThreadLocal存储当前线程的数据源名。
public final class DynamicDataSourceContextHolder { @SuppressWarnings("unchecked") private static final ThreadLocal<Deque<String>> LOOKUP_KEY_HOLDER = new ThreadLocal() { @Override protected Object initialValue() { return new ArrayDeque(); } }; private DynamicDataSourceContextHolder() { } public static String peek() { return LOOKUP_KEY_HOLDER.get().peek(); } public static void push(String ds) { LOOKUP_KEY_HOLDER.get().push(StringUtils.isEmpty(ds) ? "" : ds); } public static void poll() { Deque<String> deque = LOOKUP_KEY_HOLDER.get(); deque.poll(); if (deque.isEmpty()) { LOOKUP_KEY_HOLDER.remove(); } } public static void clear() { LOOKUP_KEY_HOLDER.remove(); }}进行数据操作时，会调用org.springframework.jdbc.datasource.getConnection()方法；getConnection()方法最终调用了com.baomidou.dynamic.datasource.AbstractRoutingDataSource的getConnection()方法；
@Override public Connection getConnection() throws SQLException { return determineDataSource().getConnection(); }determineDataSource()由子类com.baomidou.dynamic.datasource.DynamicRoutingDataSource实现，可以看到DynamicRoutingDataSource从DynamicDataSourceContextHolder获取数据源名称，这个在之前拦截器处理存进ThreadLocal中，如果有数据源名称则从dataSourceMap中获取，没有则获取默认的primary数据源。
public DataSource determineDataSource() { return getDataSource(DynamicDataSourceContextHolder.peek());}public DataSource getDataSource(String ds) { if (StringUtils.isEmpty(ds)) { return determinePrimaryDataSource(); } else if (!groupDataSources.isEmpty() && groupDataSources.containsKey(ds)) { log.debug("dynamic-datasource switch to the datasource named [{}]", ds); return groupDataSources.get(ds).determineDataSource(); } else if (dataSourceMap.containsKey(ds)) { log.debug("dynamic-datasource switch to the datasource named [{}]", ds); return dataSourceMap.get(ds); } if (strict) { throw new RuntimeException("dynamic-datasource could not find a datasource named" + ds); } return determinePrimaryDataSource();}private DataSource determinePrimaryDataSource() { log.debug("dynamic-datasource switch to the primary datasource"); return groupDataSources.containsKey(primary) ? groupDataSources.get(primary) .determineDataSource() : dataSourceMap.get(primary);}此时的数据源已经切换成了我们需要的数据源。
数据操作完成后，方法返回第二步中的拦截器，执行DynamicDataSourceContextHolder.poll();清除掉此次的数据源，避免影响后续数据操作。
附上动态数据源相关配置
spring: application: name: datasource: dynamic: primary: dataSource1 datasource: dataSource1: type: com.alibaba.druid.pool.DruidDataSource driverClassName: com.microsoft.sqlserver.jdbc.SQLServerDriver url: jdbc:sqlserver://localhost:1433;database=dataSource1 username: password: dataSource2: type: com.alibaba.druid.pool.DruidDataSource driverClassName: com.microsoft.sqlserver.jdbc.SQLServerDriver url: jdbc:sqlserver://localhost:1433;instanceName=sqlserver2017;DatabaseName=dataSource2 username: password:pom.xml
<dependency> <groupId>com.baomidou</groupId> <artifactId>dynamic-datasource-spring-boot-starter</artifactId> <version>2.5.6</version></dependency>相应类
@Service//@DS("dataSource2") 放在类上就是类下所有方法都使用这个数据源。public class XXXServiceImpl extends BaseServiceImpl<XXXMapper, XXXBean> implements XXXService { @DS("dataSource1") public void selectDataFromSource1() { // do somethinng; } @DS("dataSource2") public void selectDataFromSource1() { // do somethinng; }}**注意：**不可在事务中切换数据库，保证事务需要方法使用同一连接，使用@DS(dataSource1)方法调用@DS(dataSource2)无法切换连接，会导致方法报错。
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