循环依赖检测方法 spring源码方法

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本文介绍了一种检查别名循环的方法，并提供了一个简单的别名注册系统的实现案例。通过递归查找，确保不会出现从名称到别名的循环引用，有效避免了因别名映射不当而导致的问题。

场景：checkForAliasCircle(name, alias);
this.aliasMap.put(alias, name);

A,B
B,C
当准备存入 C, A时，执行checkForAliasCircle 检验是否构成key-value循环

代码实现检测方式：

public class SimpleAliasRegistry implements AliasRegistry {

/** Map from alias to canonical name */
private final Map<String, String> aliasMap = new ConcurrentHashMap<String, String>(16);

/**
* Determine the raw name, resolving aliases to canonical names.
* @param name the user-specified name
* @return the transformed name
*/
public String canonicalName(String name) {
String canonicalName = name;
// Handle aliasing...
String resolvedName;
do {
resolvedName = this.aliasMap.get(canonicalName);
if (resolvedName != null) {
canonicalName = resolvedName;
}
}
while (resolvedName != null);
return canonicalName;
}

/**
* Check whether the given name points back to given alias as an alias
* in the other direction, catching a circular reference upfront and
* throwing a corresponding IllegalStateException.
* @param name the candidate name
* @param alias the candidate alias
* @see #registerAlias
*/
protected void checkForAliasCircle(String name, String alias) {
if (alias.equals(canonicalName(name))) {
throw new IllegalStateException("Cannot register alias '" + alias +
"' for name '" + name + "': Circular reference - '" +
name + "' is a direct or indirect alias for '" + alias + "' already");
}
}