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/**
* Simple implementation of the {@link AliasRegistry} interface.
* Serves as base class for
* {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
* implementations.
*
* @author Juergen Hoeller
* @since 2.5.2
*/
public class SimpleAliasRegistry implements AliasRegistry {
/**
* Logger available to subclasses.
*/
protected final Log logger = LogFactory.getLog(getClass());
/**
* Map from alias to canonical name.
* 存放别名的map(线程安全的),
* 结构: alias-> name
*/
private final Map<String, String> aliasMap = new ConcurrentHashMap<>(16);
/**
* {@code <alias name="appleBean" alias="hhh"/>}
*
* @param name the canonical name
* alias 标签的name属性
* @param alias the alias to be registered
* alias 标签的alias属性
*/
@Override
public void registerAlias(String name, String alias) {
Assert.hasText(name, "'name' must not be empty");
Assert.hasText(alias, "'alias' must not be empty");
synchronized (this.aliasMap) {
// 判断: 别名和名字是否相同
if (alias.equals(name)) {
//相同在别名map中移除
this.aliasMap.remove(alias);
if (logger.isDebugEnabled()) {
logger.debug("Alias definition '" + alias + "' ignored since it points to same name");
}
}
else {
// 不相同
// 从map对象中获取别名为alias的value
String registeredName = this.aliasMap.get(alias);
if (registeredName != null) {
// 判断map中是否有有一个别名和传入的name相同的内容
if (registeredName.equals(name)) {
// An existing alias - no need to re-register
return;
}
if (!allowAliasOverriding()) {
throw new IllegalStateException("Cannot define alias '" + alias + "' for name '" +
name + "': It is already registered for name '" + registeredName + "'.");
}
if (logger.isDebugEnabled()) {
logger.debug("Overriding alias '" + alias + "' definition for registered name '" +
registeredName + "' with new target name '" + name + "'");
}
}
// 别名环检查
checkForAliasCircle(name, alias);
// 放入 map 对象中 alias-> name
this.aliasMap.put(alias, name);
if (logger.isTraceEnabled()) {
logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");
}
}
}
}
/**
* Return whether alias overriding is allowed.
* Default is {@code true}.
* 是否允许重写别名
*/
protected boolean allowAliasOverriding() {
return true;
}
/**
* Determine whether the given name has the given alias registered.
* <p>
* 递归判断是否已经存在别名
*
* @param name the name to check
* @param alias the alias to look for
* @since 4.2.1
*/
public boolean hasAlias(String name, String alias) {
for (Map.Entry<String, String> entry : this.aliasMap.entrySet()) {
// 获取key值
String registeredName = entry.getValue();
if (registeredName.equals(name)) {
String registeredAlias = entry.getKey();
// 循环引用判断
if (registeredAlias.equals(alias) || hasAlias(registeredAlias, alias)) {
return true;
}
}
}
return false;
}
/**
* 别名移除
*
* @param alias the alias to remove
*/
@Override
public void removeAlias(String alias) {
synchronized (this.aliasMap) {
// 判断是否移除成功
String name = this.aliasMap.remove(alias);
if (name == null) {
throw new IllegalStateException("No alias '" + alias + "' registered");
}
}
}
/**
* 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
*
* @param name the name to check
* @return
*/
@Override
public boolean isAlias(String name) {
return this.aliasMap.containsKey(name);
}
/**
* 获取别名列表
*
* @param name the name to check for aliases
* @return
*/
@Override
public String[] getAliases(String name) {
List<String> result = new ArrayList<>();
synchronized (this.aliasMap) {
retrieveAliases(name, result);
}
return StringUtils.toStringArray(result);
}
/**
* Transitively retrieve all aliases for the given name.
* 根据 name 获取别名
*
* @param name the target name to find aliases for
* @param result the resulting aliases list
*/
private void retrieveAliases(String name, List<String> result) {
// 循环获取
this.aliasMap.forEach((alias, registeredName) -> {
if (registeredName.equals(name)) {
result.add(alias);
// 递归查询循环引用的别名
retrieveAliases(alias, result);
}
});
}
/**
* Resolve all alias target names and aliases registered in this
* factory, applying the given StringValueResolver to them.
* <p>The value resolver may for example resolve placeholders
* in target bean names and even in alias names.
*
* @param valueResolver the StringValueResolver to apply
*/
public void resolveAliases(StringValueResolver valueResolver) {
Assert.notNull(valueResolver, "StringValueResolver must not be null");
synchronized (this.aliasMap) {
Map<String, String> aliasCopy = new HashMap<>(this.aliasMap);
aliasCopy.forEach((alias, registeredName) -> {
String resolvedAlias = valueResolver.resolveStringValue(alias);
String resolvedName = valueResolver.resolveStringValue(registeredName);
if (resolvedAlias == null || resolvedName == null || resolvedAlias.equals(resolvedName)) {
this.aliasMap.remove(alias);
}
else if (!resolvedAlias.equals(alias)) {
String existingName = this.aliasMap.get(resolvedAlias);
if (existingName != null) {
if (existingName.equals(resolvedName)) {
// Pointing to existing alias - just remove placeholder
this.aliasMap.remove(alias);
return;
}
throw new IllegalStateException(
"Cannot register resolved alias '" + resolvedAlias + "' (original: '" + alias +
"') for name '" + resolvedName + "': It is already registered for name '" +
registeredName + "'.");
}
checkForAliasCircle(resolvedName, resolvedAlias);
this.aliasMap.remove(alias);
this.aliasMap.put(resolvedAlias, resolvedName);
}
else if (!registeredName.equals(resolvedName)) {
this.aliasMap.put(alias, resolvedName);
}
});
}
}
/**
* Check whether the given name points back to the given alias as an alias
* in the other direction already, catching a circular reference upfront
* and throwing a corresponding IllegalStateException.
* <p>
* 判断是否循环别名
*
* @param name the candidate name
* @param alias the candidate alias
* @see #registerAlias
* @see #hasAlias
*/
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");
}
}
/**
* 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;
}
}
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