Spring + Mybatis Dynamic DataSource

为了做隔离性比较好的multi-tenant app，决定做schema based multi-tenant，这就需要

• Runtime切换DataSource
• 为了使添加新tenant不用重启，最好还能实现Runtime添加DataSource

所以分2步实现这两个功能。

代码：https://github.com/fanjingdan012/ssm
目前有3个branch

• master是基础版Spring+Mybatis+Mariadb，能Read一个DataSource
• multi-data-source是实现Runtime切换DataSource的
• multi-tenant是实现现Runtime添加DataSource的

预先定义DataSource，Runtime切换

效果

• 数据库准备，这里用了mariadb，用了两个schema， test和test2，里面是同样的一张member表，插入一点不同的数据
  
• 用header控制Tenant-ID，从而访问不同的DataSource
  

  代码

  写一个MultitenantDataSource.java, MultitenantDataSource extends AbstractRoutingDataSource

看一下AbstractRoutingDataSource的源代码

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;
}

里面有一个resolvedDataSources的Map，存储了多个DataSource，会调用determineCurrentLookupKey()来Runtime决定使用哪个DataSource，如果没有指定的那个Key，那么就会使用DefaultDataSource
所以使用它就是需要

• Override determineCurrentLookupKey()方法，定义tenantId作为key

  public class MultitenantDataSource extends AbstractRoutingDataSource {
      @Override
      protected Object determineCurrentLookupKey() {
          return TenantContext.getCurrentTenant();
      }
  }

• 调用setTargetDataSources方法去把Map填进去
• 调用setDefaultTargetDataSource 方法把DefaultDataSource设置好，最好是将DefaultDataSource设置成tenant管理数据库，保存tenant相关信息，但是作为一个demo，本项目就比较简单，直接把它设为一个tenant数据库

  @Configuration
  public class MultitenantConfiguration {
  
      @Bean
      public MultitenantDataSource multitenantDataSource() {
          Map<Object,Object> resolvedDataSources = new HashMap<>();
          //db1
          DataSourceBuilder dataSourceBuilder = DataSourceBuilder.create()
                  .url("jdbc:mysql://localhost/test")
                  .username("root")
                  .password("******");
          resolvedDataSources.put("tenant1",dataSourceBuilder.build());
          resolvedDataSources.put("Default",dataSourceBuilder.build());
  
          //db2
          DataSourceBuilder dataSourceBuilder2 = DataSourceBuilder.create()
                  .url("jdbc:mysql://localhost/test2")
                  .username("root")
                  .password("******");
          resolvedDataSources.put("tenant2",dataSourceBuilder2.build());
  
  
          MultitenantDataSource dataSource = new MultitenantDataSource();
          dataSource.setDefaultTargetDataSource(resolvedDataSources.get("Default"));
          dataSource.setTargetDataSources(resolvedDataSources);
  
  
          dataSource.afterPropertiesSet();
  
          return dataSource;
      }

• 在Controller里添加从header读取tenantId的逻辑
  XXController.java

  public Member member(@PathVariable("name") String name, @RequestHeader("X-TenantID") String tenantName){
  	TenantContext.setCurrentTenant(tenantName);
  ...
  }

Runtime 添加DataSource

效果

• 注册新的tenant，直接把jdbc url，username， password通过request parameter传入，返回success
• 通过header控制tenantId，访问新的tenant（DataSource）的数据
  

  代码

• 写一个MultitenantDataSourceRegister.java (implements ImportBeanDefinitionRegistrar), 就要实现 registerBeanDefinitions方法

  public void registerBeanDefinitions(AnnotationMetadata annotaion, BeanDefinitionRegistry registry) {
      System.out.println("registerBeanDefinitions");
      GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
      beanDefinition.setBeanClass(MultitenantDataSource.class);
      beanDefinition.setSynthetic(true);
      MutablePropertyValues mpv = beanDefinition.getPropertyValues();
  
      mpv.addPropertyValue("defaultTargetDataSource", getDefaultDataSources().get("Default"));
      mpv.addPropertyValue("targetDataSources",getDefaultDataSources());
      registry.registerBeanDefinition("dataSource", beanDefinition);
  }

• 在 MultitenantConfiguration上添加@Import(MultitenantDataSourceRegister.class)

  @Configuration
  @Import(MultitenantDataSourceRegister.class)
  public class MultitenantConfiguration {
  
      @Autowired
      private MultitenantDataSource multitenantDataSource;
  
  }

• 在MultitenantDataSource里维护一个Map用来管理DataSources

  public class MultitenantDataSource extends AbstractRoutingDataSource {
      @Override
      protected Object determineCurrentLookupKey() {
          return TenantContext.getCurrentTenant();
      }
      private ConcurrentHashMap<String, DataSource> backupTargetDataSources = new ConcurrentHashMap<>();
  
      public void addDataSourceToTargetDataSource(String key ,DataSource ds){
          this.backupTargetDataSources.put(key, ds);
          this.setTargetDataSource(this.backupTargetDataSources);
      }
  
  
      public void setTargetDataSource(Map targetDataSource){
          super.setTargetDataSources(targetDataSource);
          this.afterPropertiesSet();
      }
  }

• 在XXController里添加注册DataSource的API

  @GetMapping("/api/tenant/register")
  @ResponseBody
  public String tenantRegister(@RequestParam String username, @RequestParam String password, @RequestParam String url, @RequestParam String tenantName) {
  	MultitenantDataSource multitenantDataSource = ctx.getBean(MultitenantDataSource.class);
  	DataSourceBuilder dataSourceBuilder = DataSourceBuilder.create()
  			.url(url)
  			.username(username)
  			.password(password);
  	multitenantDataSource.addDataSourceToTargetDataSource(tenantName, dataSourceBuilder.build());
  	return "success";
  }