mybatis-spring-2.0.5 MapperScannerConfigurer 导致brcc多次加载

[ghzengqy568]

现象：
引入mybatis-spring-boot-starter 2.1.3 （对应mybatis-spring 2.0.5）后， 在多数据源情况下sdk多次加载brcc配置。
问题分析：
项目中多数据源情况下， 通过@MapperScan指定扫描不同的package和sqlSessionFactory, @MapperScan -> @import(MapperScannerRegistrar.class) -> MapperScannerConfigurer
MapperScannerConfigurer 实现了BeanDefinitionRegistryPostProcessor接口， 在配置processPropertyPlaceHolders为true的情况下会调用processPropertyPlaceHolders()方法
`
private void processPropertyPlaceHolders() {
// 获取到brcc的ConfigCenterPropertyPlaceholderConfigurer
Map<String, PropertyResourceConfigurer> prcs = applicationContext.getBeansOfType(PropertyResourceConfigurer.class,
false, false);

if (!prcs.isEmpty() && applicationContext instanceof ConfigurableApplicationContext) {
  BeanDefinition mapperScannerBean = ((ConfigurableApplicationContext) applicationContext).getBeanFactory()
      .getBeanDefinition(beanName);

  // PropertyResourceConfigurer does not expose any methods to explicitly perform
  // property placeholder substitution. Instead, create a BeanFactory that just
  // contains this mapper scanner and post process the factory.
  DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
  factory.registerBeanDefinition(beanName, mapperScannerBean);

  for (PropertyResourceConfigurer prc : prcs.values()) {
    // 主动调用brcc替换mapperScannerBean中的属性
    prc.postProcessBeanFactory(factory);
  }

  PropertyValues values = mapperScannerBean.getPropertyValues();

  this.basePackage = updatePropertyValue("basePackage", values);
  this.sqlSessionFactoryBeanName = updatePropertyValue("sqlSessionFactoryBeanName", values);
  this.sqlSessionTemplateBeanName = updatePropertyValue("sqlSessionTemplateBeanName", values);
  this.lazyInitialization = updatePropertyValue("lazyInitialization", values);
}
this.basePackage = Optional.ofNullable(this.basePackage).map(getEnvironment()::resolvePlaceholders).orElse(null);
this.sqlSessionFactoryBeanName = Optional.ofNullable(this.sqlSessionFactoryBeanName)
    .map(getEnvironment()::resolvePlaceholders).orElse(null);
this.sqlSessionTemplateBeanName = Optional.ofNullable(this.sqlSessionTemplateBeanName)
    .map(getEnvironment()::resolvePlaceholders).orElse(null);
this.lazyInitialization = Optional.ofNullable(this.lazyInitialization).map(getEnvironment()::resolvePlaceholders)
    .orElse(null);

}

`
这样导致了brcc多次远程调用

[ghzengqy568]

现象：
引入mybatis-spring-boot-starter 2.1.3 （对应mybatis-spring 2.0.5）后， 在多数据源情况下sdk多次加载brcc配置。
问题分析：
项目中多数据源情况下， 通过@MapperScan指定扫描不同的package和sqlSessionFactory, @MapperScan -> @import(MapperScannerRegistrar.class) -> MapperScannerConfigurer
MapperScannerConfigurer 实现了BeanDefinitionRegistryPostProcessor接口， 在配置processPropertyPlaceHolders为true的情况下会调用processPropertyPlaceHolders()方法
`
private void processPropertyPlaceHolders() {
// 获取到brcc的ConfigCenterPropertyPlaceholderConfigurer
Map<String, PropertyResourceConfigurer> prcs = applicationContext.getBeansOfType(PropertyResourceConfigurer.class,
false, false);

if (!prcs.isEmpty() && applicationContext instanceof ConfigurableApplicationContext) {
  BeanDefinition mapperScannerBean = ((ConfigurableApplicationContext) applicationContext).getBeanFactory()
      .getBeanDefinition(beanName);

  // PropertyResourceConfigurer does not expose any methods to explicitly perform
  // property placeholder substitution. Instead, create a BeanFactory that just
  // contains this mapper scanner and post process the factory.
  DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
  factory.registerBeanDefinition(beanName, mapperScannerBean);

  for (PropertyResourceConfigurer prc : prcs.values()) {
    // 主动调用brcc替换mapperScannerBean中的属性
    prc.postProcessBeanFactory(factory);
  }

  PropertyValues values = mapperScannerBean.getPropertyValues();

  this.basePackage = updatePropertyValue("basePackage", values);
  this.sqlSessionFactoryBeanName = updatePropertyValue("sqlSessionFactoryBeanName", values);
  this.sqlSessionTemplateBeanName = updatePropertyValue("sqlSessionTemplateBeanName", values);
  this.lazyInitialization = updatePropertyValue("lazyInitialization", values);
}
this.basePackage = Optional.ofNullable(this.basePackage).map(getEnvironment()::resolvePlaceholders).orElse(null);
this.sqlSessionFactoryBeanName = Optional.ofNullable(this.sqlSessionFactoryBeanName)
    .map(getEnvironment()::resolvePlaceholders).orElse(null);
this.sqlSessionTemplateBeanName = Optional.ofNullable(this.sqlSessionTemplateBeanName)
    .map(getEnvironment()::resolvePlaceholders).orElse(null);
this.lazyInitialization = Optional.ofNullable(this.lazyInitialization).map(getEnvironment()::resolvePlaceholders)
    .orElse(null);

}

`
这样导致了brcc多次远程调用

sdk中添加加载标志，当第一次加载成功后加载标志设置为true，后面加不再加载