huifer
5 years ago
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# Spring-SimpleAliasRegistry
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- Author: [HuiFer](https://github.com/huifer)
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- 源码阅读仓库: [huifer-spring](https://github.com/huifer/spring-framework)
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## AliasRegistry
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- `SimpleAliasRegistry`继承`org.springframework.core.AliasRegistry`
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```java
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public interface AliasRegistry {
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/**
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* Given a name, register an alias for it.
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* 别名注册
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*
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* @param name the canonical name
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* @param alias the alias to be registered
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* @throws IllegalStateException if the alias is already in use
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* and may not be overridden
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* @see SimpleAliasRegistry
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* @see org.springframework.context.support.GenericApplicationContext
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*/
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void registerAlias(String name, String alias);
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/**
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* Remove the specified alias from this registry.
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* 别名移除
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*
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* @param alias the alias to remove
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* @throws IllegalStateException if no such alias was found
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*/
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void removeAlias(String alias);
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/**
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* Determine whether this given name is defines as an alias
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* (as opposed to the name of an actually registered component).
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* 是不是别名
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*
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* @param name the name to check
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* @return whether the given name is an alias
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*/
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boolean isAlias(String name);
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/**
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* Return the aliases for the given name, if defined.
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* 从别名注册map中获取别名信息
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*
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* @param name the name to check for aliases
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* @return the aliases, or an empty array if none
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*/
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String[] getAliases(String name);
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}
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```
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## SimpleAliasRegistry
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```java
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/**
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* Simple implementation of the {@link AliasRegistry} interface.
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* Serves as base class for
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* {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
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* implementations.
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*
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* @author Juergen Hoeller
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* @since 2.5.2
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*/
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public class SimpleAliasRegistry implements AliasRegistry {
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/**
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* Logger available to subclasses.
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*/
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protected final Log logger = LogFactory.getLog(getClass());
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/**
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* Map from alias to canonical name.
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* 存放别名的map(线程安全的),
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* 结构: alias-> name
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*/
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private final Map<String, String> aliasMap = new ConcurrentHashMap<>(16);
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/**
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* {@code <alias name="appleBean" alias="hhh"/>}
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*
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* @param name the canonical name
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* alias 标签的name属性
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* @param alias the alias to be registered
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* alias 标签的alias属性
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*/
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@Override
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public void registerAlias(String name, String alias) {
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Assert.hasText(name, "'name' must not be empty");
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Assert.hasText(alias, "'alias' must not be empty");
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synchronized (this.aliasMap) {
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// 判断: 别名和名字是否相同
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if (alias.equals(name)) {
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//相同在别名map中移除
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this.aliasMap.remove(alias);
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if (logger.isDebugEnabled()) {
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logger.debug("Alias definition '" + alias + "' ignored since it points to same name");
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}
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}
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else {
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// 不相同
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// 从map对象中获取别名为alias的value
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String registeredName = this.aliasMap.get(alias);
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if (registeredName != null) {
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// 判断map中是否有有一个别名和传入的name相同的内容
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if (registeredName.equals(name)) {
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// An existing alias - no need to re-register
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return;
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}
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if (!allowAliasOverriding()) {
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throw new IllegalStateException("Cannot define alias '" + alias + "' for name '" +
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name + "': It is already registered for name '" + registeredName + "'.");
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}
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if (logger.isDebugEnabled()) {
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logger.debug("Overriding alias '" + alias + "' definition for registered name '" +
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registeredName + "' with new target name '" + name + "'");
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}
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}
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// 别名环检查
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checkForAliasCircle(name, alias);
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// 放入 map 对象中 alias-> name
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this.aliasMap.put(alias, name);
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if (logger.isTraceEnabled()) {
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logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");
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}
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}
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}
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}
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/**
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* Return whether alias overriding is allowed.
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* Default is {@code true}.
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* 是否允许重写别名
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*/
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protected boolean allowAliasOverriding() {
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return true;
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}
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/**
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* Determine whether the given name has the given alias registered.
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* <p>
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* 递归判断是否已经存在别名
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*
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* @param name the name to check
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* @param alias the alias to look for
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* @since 4.2.1
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*/
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public boolean hasAlias(String name, String alias) {
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for (Map.Entry<String, String> entry : this.aliasMap.entrySet()) {
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// 获取key值
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String registeredName = entry.getValue();
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if (registeredName.equals(name)) {
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String registeredAlias = entry.getKey();
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// 循环引用判断
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if (registeredAlias.equals(alias) || hasAlias(registeredAlias, alias)) {
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return true;
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}
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}
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}
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return false;
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}
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/**
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* 别名移除
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*
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* @param alias the alias to remove
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*/
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@Override
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public void removeAlias(String alias) {
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synchronized (this.aliasMap) {
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// 判断是否移除成功
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String name = this.aliasMap.remove(alias);
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if (name == null) {
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throw new IllegalStateException("No alias '" + alias + "' registered");
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}
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}
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}
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/**
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* 判断是否是一个别名,校验方式{@link org.springframework.core.SimpleAliasRegistry#aliasMap} 的key是否包含
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*
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* @param name the name to check
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* @return
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*/
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@Override
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public boolean isAlias(String name) {
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return this.aliasMap.containsKey(name);
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}
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/**
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* 获取别名列表
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*
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* @param name the name to check for aliases
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* @return
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*/
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@Override
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public String[] getAliases(String name) {
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List<String> result = new ArrayList<>();
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synchronized (this.aliasMap) {
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retrieveAliases(name, result);
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}
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return StringUtils.toStringArray(result);
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}
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/**
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* Transitively retrieve all aliases for the given name.
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* 根据 name 获取别名
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*
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* @param name the target name to find aliases for
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* @param result the resulting aliases list
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*/
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private void retrieveAliases(String name, List<String> result) {
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// 循环获取
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this.aliasMap.forEach((alias, registeredName) -> {
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if (registeredName.equals(name)) {
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result.add(alias);
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// 递归查询循环引用的别名
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retrieveAliases(alias, result);
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}
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});
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}
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/**
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* Resolve all alias target names and aliases registered in this
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* factory, applying the given StringValueResolver to them.
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* <p>The value resolver may for example resolve placeholders
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* in target bean names and even in alias names.
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*
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* @param valueResolver the StringValueResolver to apply
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*/
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public void resolveAliases(StringValueResolver valueResolver) {
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Assert.notNull(valueResolver, "StringValueResolver must not be null");
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synchronized (this.aliasMap) {
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Map<String, String> aliasCopy = new HashMap<>(this.aliasMap);
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aliasCopy.forEach((alias, registeredName) -> {
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String resolvedAlias = valueResolver.resolveStringValue(alias);
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String resolvedName = valueResolver.resolveStringValue(registeredName);
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if (resolvedAlias == null || resolvedName == null || resolvedAlias.equals(resolvedName)) {
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this.aliasMap.remove(alias);
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}
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else if (!resolvedAlias.equals(alias)) {
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String existingName = this.aliasMap.get(resolvedAlias);
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if (existingName != null) {
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if (existingName.equals(resolvedName)) {
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// Pointing to existing alias - just remove placeholder
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this.aliasMap.remove(alias);
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return;
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}
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throw new IllegalStateException(
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"Cannot register resolved alias '" + resolvedAlias + "' (original: '" + alias +
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"') for name '" + resolvedName + "': It is already registered for name '" +
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registeredName + "'.");
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}
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checkForAliasCircle(resolvedName, resolvedAlias);
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this.aliasMap.remove(alias);
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this.aliasMap.put(resolvedAlias, resolvedName);
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}
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else if (!registeredName.equals(resolvedName)) {
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this.aliasMap.put(alias, resolvedName);
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}
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});
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}
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}
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/**
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* Check whether the given name points back to the given alias as an alias
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* in the other direction already, catching a circular reference upfront
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* and throwing a corresponding IllegalStateException.
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* <p>
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* 判断是否循环别名
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*
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* @param name the candidate name
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* @param alias the candidate alias
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* @see #registerAlias
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* @see #hasAlias
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*/
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protected void checkForAliasCircle(String name, String alias) {
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if (hasAlias(alias, name)) {
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throw new IllegalStateException("Cannot register alias '" + alias +
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"' for name '" + name + "': Circular reference - '" +
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name + "' is a direct or indirect alias for '" + alias + "' already");
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}
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}
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/**
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* Determine the raw name, resolving aliases to canonical names.
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*
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* @param name the user-specified name
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* @return the transformed name
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*/
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public String canonicalName(String name) {
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String canonicalName = name;
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// Handle aliasing...
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String resolvedName;
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do {
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resolvedName = this.aliasMap.get(canonicalName);
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if (resolvedName != null) {
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canonicalName = resolvedName;
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}
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}
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while (resolvedName != null);
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return canonicalName;
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}
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}
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```
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