声明:接口简单介绍、着重介绍其实现类
本文分析的内容为
AliasRegistry接口中的源码
package org.springframework.core;
/**
* Common interface for managing aliases. Serves as super-interface for
* {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}.
*
* @author Juergen Hoeller
* @since 2.5.2
*/
public interface AliasRegistry {
/**
* Given a name, register an alias for it.
* @param name the canonical name
* @param alias the alias to be registered
* @throws IllegalStateException if the alias is already in use
* and may not be overridden
*
* JustryDeng概述:
* 给name注册别名alias
*/
void registerAlias(String name, String alias);
/**
* Remove the specified alias from this registry.
* @param alias the alias to remove
* @throws IllegalStateException if no such alias was found
*
* JustryDeng概述:
* 删除别名alias
*/
void removeAlias(String alias);
/**
* Determine whether this given name is defines as an alias
* (as opposed to the name of an actually registered component).
* @param name the name to check
* @return whether the given name is an alias
*
* JustryDeng概述:
* 判断name是否是别名
*/
boolean isAlias(String name);
/**
* Return the aliases for the given name, if defined.
* @param name the name to check for aliases
* @return the aliases, or an empty array if none
*
* JustryDeng概述:
* 获取name的所有别名
*/
String[] getAliases(String name);
}SimpleAliasRegistry类中的源码
/**
* 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 {
/** Map from alias to canonical name */
/** 用于存放alias(key)以及 与其对应的name(value) */
private final Map<String, String> aliasMap = new ConcurrentHashMap<String, String>(16);
@Override
public void registerAlias(String name, String alias) {
Assert.hasText(name, "'name' must not be empty");
Assert.hasText(alias, "'alias' must not be empty");
if (alias.equals(name)) {
this.aliasMap.remove(alias);
}
else {
String registeredName = this.aliasMap.get(alias);
if (registeredName != null) {
if (registeredName.equals(name)) {
// An existing alias - no need to re-register
return;
}
if (!allowAliasOverriding()) {
throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" +
name + "': It is already registered for name '" + registeredName + "'.");
}
}
checkForAliasCircle(name, alias);
this.aliasMap.put(alias, name);
}
}
/**
* Return whether alias overriding is allowed.
* Default is {@code true}.
*
* JustryDeng: 是否允许新的别名覆盖旧的别名
*/
protected boolean allowAliasOverriding() {
return true;
}
/**
* Determine whether the given name has the given alias registered.
* @param name the name to check
* @param alias the alias to look for
* @since 4.2.1
*
* JustryDeng: 判断name是否具有别名alias
*/
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();
return (registeredAlias.equals(alias) || hasAlias(registeredAlias, alias));
}
}
return false;
}
@Override
public void removeAlias(String alias) {
String name = this.aliasMap.remove(alias);
if (name == null) {
throw new IllegalStateException("No alias '" + alias + "' registered");
}
}
@Override
public boolean isAlias(String name) {
return this.aliasMap.containsKey(name);
}
@Override
public String[] getAliases(String name) {
List<String> result = new ArrayList<String>();
synchronized (this.aliasMap) {
retrieveAliases(name, result);
}
return StringUtils.toStringArray(result);
}
/**
* Transitively retrieve all aliases for the given name.
* @param name the target name to find aliases for
* @param result the resulting aliases list
*
* JustryDeng: 查询指定name的所有别名,并存入result集合中
* 注:存在将alia1作为name1,又给这个name1添加了alia2的别名 的情况.所以这里递归调用.
*/
private void retrieveAliases(String name, List<String> result) {
for (Map.Entry<String, String> entry : this.aliasMap.entrySet()) {
String registeredName = entry.getValue();
if (registeredName.equals(name)) {
String alias = entry.getKey();
result.add(alias);
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
*
* JustryDeng: 解析alias、name(主要是解析占位符之类的);
* 并以解析后的alias、name为主,清理aliasMap中的某些不该存在的数据
*/
public void resolveAliases(StringValueResolver valueResolver) {
Assert.notNull(valueResolver, "StringValueResolver must not be null");
// 同步代码块儿,这里指明需要:aliasMap的对象锁
synchronized (this.aliasMap) {
Map<String, String> aliasCopy = new HashMap<String, String>(this.aliasMap);
for (String alias : aliasCopy.keySet()) {
String registeredName = aliasCopy.get(alias);
// 解析给定的String值,例如:解析占位符等。
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);
break;
}
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.
* @param name the candidate name
* @param alias the candidate alias
* @see #registerAlias
* @see #hasAlias
*
* JustryDeng: 判断name是否具有别名alias,如果具有,那么抛出异常
* 注:传入此方法的alias,可能是直接的(即解析前的)别名,也可能是间接的(即解析后的)别名
*/
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
*
* JustryDeng-译:将别名解析为规范名称。
*/
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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