mybatis-plus @DS實現動態切換資料來源原理

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 {

  /**
   * 為什麼要用連結串列儲存(準確的是棧)
   * 為了支援巢狀切換，如ABC三個service都是不同的資料來源
   * 其中A的某個業務要調B的方法，B的方法需要呼叫C的方法。一級一級呼叫切換，形成了鏈。
   * 傳統的只設定當前執行緒的方式不能滿足此業務需求，必須模擬棧，後進先出。
   */
  @SuppressWarnings("unchecked")
  private static final ThreadLocal<Deque<String>> LOOKUP_KEY_HOLDER = new ThreadLocal() {
    @Override
    protected Object initialValue() {
      return new ArrayDeque();
    }
  };

  private DynamicDataSourceContextHolder() {
  }

  /**
   * 獲得當前執行緒資料來源
   * @return 資料來源名稱
   */
  public static String peek() {
    return LOOKUP_KEY_HOLDER.get().peek();
  }

  /**
   * 設定當前執行緒資料來源
   * 如非必要不要手動呼叫，呼叫後確保最終清除
   * @param ds 資料來源名稱
   */
  public static void push(String ds) {
    LOOKUP_KEY_HOLDER.get().push(StringUtils.isEmpty(ds) ? "" : ds);
  }

  /**
   * 清空當前執行緒資料來源
   * 如果當前執行緒是連續切換資料來源 只會移除掉當前執行緒的資料來源名稱
   */
  public static void poll() {
    Deque<String> deque = LOOKUP_KEY_HOLDER.get();
    deque.poll();
    if (deque.isEmpty()) {
      LOOKUP_KEY_HOLDER.remove();
    }
  }

  /**
   * 強制清空本地執行緒
   * 防止記憶體漏失，如手動呼叫了push可呼叫此方法確保清除
   */
  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") 放在類上就是類下所有方法都使用這個資料來源。
public class XXXServiceImpl extends BaseServiceImpl<XXXMapper, XXXBean> implements XXXService {

    @DS("dataSource1")
    public void selectDataFromSource1() {
       // do somethinng;
    }
    
    @DS("dataSource2")
    public void selectDataFromSource1() {
       // do somethinng;
    }
}