mybatis-plus @DS实现动态切换数据源原理

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);
  }

public class DynamicDataSourceAnnotationInterceptor implements MethodInterceptor {

  /**
   * The identification of SPEL.
   */
  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;
  }
}

public final class DynamicDataSourceContextHolder {

  /**
   * 为什么要用链表存储(准确的是栈)
   * 为了支持嵌套切换，如ABC三个service都是不同的数据源
   * 其中A的某个业务要调B的方法，B的方法需要调用C的方法。一级一级调用切换，形成了链。
   * 传统的只设置当前线程的方式不能满足此业务需求，必须模拟栈，后进先出。
   */
  @SuppressWarnings("unchecked")
  private static final ThreadLocal<Deque<String>> LOOKUP_KEY_HOLDER = new ThreadLocal() {
    @Override
    protected Object initialValue() {
      return new ArrayDeque();
    }
  };

  private DynamicDataSourceContextHolder() {
  }

  /**
   * 获得当前线程数据源
   * @return 数据源名称
   */
  public static String peek() {
    return LOOKUP_KEY_HOLDER.get().peek();
  }

  /**
   * 设置当前线程数据源
   * 如非必要不要手动调用，调用后确保最终清除
   * @param ds 数据源名称
   */
  public static void push(String ds) {
    LOOKUP_KEY_HOLDER.get().push(StringUtils.isEmpty(ds) ? "" : ds);
  }

  /**
   * 清空当前线程数据源
   * 如果当前线程是连续切换数据源 只会移除掉当前线程的数据源名称
   */
  public static void poll() {
    Deque<String> deque = LOOKUP_KEY_HOLDER.get();
    deque.poll();
    if (deque.isEmpty()) {
      LOOKUP_KEY_HOLDER.remove();
    }
  }

  /**
   * 强制清空本地线程
   * 防止内存泄漏，如手动调用了push可调用此方法确保清除
   */
  public static void clear() {
    LOOKUP_KEY_HOLDER.remove();
  }
}

  @Override
  public Connection getConnection() throws SQLException {
    return determineDataSource().getConnection();
  }

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);
}

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: 

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
    <version>2.5.6</version>
</dependency>

@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;
    }
}