checkForAliasCircle()

registerBeanDefinition注册bean定义的时候有一个判断bean别名的依赖问题

registerAlias
checkForAliasCircle(name, alias);

protected void checkForAliasCircle(String name, String alias) {
		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");
		}
	}

//之前的hasAlias方法
public boolean hasAlias(String name, String alias) {
		for (Map.Entry<String, String> entry : this.aliasMap.entrySet()) {
			String registeredName = entry.getValue();
			if (registeredName.equals(name)) {
				String registeredAlias = entry.getKey();
				if (registeredAlias.equals(alias) || hasAlias(registeredAlias, alias)) {
					return true;
				}
			}
		}
		return false;
	}


//spring 5.3.5优化了方法，也可能更早，反正现在是这个
public boolean hasAlias(String name, String alias) {
		String registeredName = this.aliasMap.get(alias);
		return ObjectUtils.nullSafeEquals(registeredName, name) || (registeredName != null
				&& hasAlias(name, registeredName));
	}

public static boolean nullSafeEquals(@Nullable Object o1, @Nullable Object o2) {
		if (o1 == o2) {
			return true;
		}
		if (o1 == null || o2 == null) {
			return false;
		}
		if (o1.equals(o2)) {
			return true;
		}
		if (o1.getClass().isArray() && o2.getClass().isArray()) {
			return arrayEquals(o1, o2);
		}
		return false;
	}

r(“2”,“1”);
r(“2”,“1”);

或者
r(“2”,“1”);
r(“3”,“2”);
r(“4”,“3”);
r(“4”,“1”);
类似这种返回true

r(“1”,“1”);
r(“3”,“1”);
这种会报错，但是已经在前面registerAlias(String name, String alias)方法中排除了

if (alias.equals(name)) {
this.aliasMap.remove(alias);
if (logger.isDebugEnabled()) {
logger.debug(“Alias definition '” + alias + “’ ignored since it points to same name”);
}
}