第五章 别名注册

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns="http://www.springframework.org/schema/beans"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">


   <alias name="people" alias="p1"/>
   <bean id="people" class="com.source.hot.ioc.book.pojo.PeopleBean">
       <property name="name" value="zhangsan"/>
   </bean>
</beans>

class AliasNodeTest {

   @Test
   void testAlias() {
       ClassPathXmlApplicationContext context
               = new ClassPathXmlApplicationContext("META-INF/alias-node.xml");

       Object people = context.getBean("people");
       Object p1 = context.getBean("p1");

       assert people.equals(p1);
   }
}

// 删除日志和验证相关代码
public void registerAlias(String name, String alias) {
    synchronized(this.aliasMap) {
        // 别名和真名是否相同
        if(alias.equals(name)) {
            // 移除
            this.aliasMap.remove(alias);
        } else {
            // 通过别名获取真名
            String registeredName = this.aliasMap.get(alias);
            // 真名不为空
            if(registeredName != null) {
                // 真名等于参数的真名
                if(registeredName.equals(name)) {
                    // An existing alias - no need to re-register
                    return;
                }
                // 是否覆盖别名
                if(!allowAliasOverriding()) {
                    throw new IllegalStateException("Cannot define alias '" + alias + "' for name '" + name + "': It is already registered for name '" + registeredName + "'.");
                }
            }
            // 别名是否循环使用
            checkForAliasCircle(name, alias);
            // 设置 别名对应真名
            this.aliasMap.put(alias, name);
        }
    }
}

protected void checkForAliasCircle(String name, String alias) {
   // 是否存在别名
   if (hasAlias(alias, name)) {
      throw new IllegalStateException("Cannot register alias '" + alias +
            "' for name '" + name + "': Circular reference - '" +
            name + "' is a direct or indirect alias for '" + alias + "' already");
   }
}

public boolean hasAlias(String name, String alias) {
   // 从别名map中获取已注册的真名
   String registeredName = this.aliasMap.get(alias);
   // 注册的真名和 参数真名是否相同,
   // 递归判断是否存在别名
   return ObjectUtils.nullSafeEquals(registeredName, name) || (registeredName != null
         && hasAlias(name, registeredName));
}

protected String transformedBeanName(String name) {
   // 转换 beanName .
   // 1. 通过·BeanFactoryUtils.transformedBeanName· 求beanName
   // 2. 如果是有别名的(方法参数是别名) . 会从别名列表中获取对应的 beanName
   return canonicalName(BeanFactoryUtils.transformedBeanName(name));
}

public static String transformedBeanName(String name) {
   Assert.notNull(name, "'name' must not be null");
   // 名字不是 & 开头直接返回
   if (!name.startsWith(BeanFactory.FACTORY_BEAN_PREFIX)) {
      return name;
   }
   // 截取字符串 在返回
   return transformedBeanNameCache.computeIfAbsent(name, beanName -> {
      do {
         beanName = beanName.substring(BeanFactory.FACTORY_BEAN_PREFIX.length());
      }
      while (beanName.startsWith(BeanFactory.FACTORY_BEAN_PREFIX));
      return beanName;
   });
}

public String canonicalName(String name) {
   String canonicalName = name;
   // Handle aliasing...
   String resolvedName;
   do {
      // 别名的获取
      resolvedName = this.aliasMap.get(canonicalName);
      if (resolvedName != null) {
         canonicalName = resolvedName;
      }
   }
   while (resolvedName != null);
   return canonicalName;
}