mybatis-plus@DS实现动态切换数据源原理

2022-11-13 12:11:51 mybatis

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。

到此这篇关于mybatis-plus @DS实现动态切换数据源原理的文章就介绍到这了,更多相关mybatis-plus @DS动态切换数据源内容请搜索以前的文章或继续浏览下面的相关文章希望大家以后多多支持!

相关文章