Spring框架之注册—SimpleAliasRegistry实现类

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一、SimpleAliasRegistry简介

SimpleAliasRegistry是AliasRegistry接口的简单实现，通过别名缓存（aliasMap）对别名的增删改查等基本实现。
二、SimpleAliasRegistry源码详解

public class SimpleAliasRegistry implements AliasRegistry {    /** 存放别名的缓存 */    private final Map<String, String> aliasMap = new ConcurrentHashMap<String, String>(16);    /**      * 给指定的Bean名称指定别名     */    @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);        }    }    /**     * 返回是否允许覆盖别名，默认为允许。     */    protected boolean allowAliasOverriding() {        return true;    }    /**     * 判断指定的Bean名称是否有指定的别名     */    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;    }    /**     * 删除指定的别名     */    @Override    public void removeAlias(String alias) {        String name = this.aliasMap.remove(alias);        if (name == null) {            throw new IllegalStateException("No alias '" + alias + "' registered");        }    }    /**     * 判断指定的名称是否为别名     */    @Override    public boolean isAlias(String name) {        return this.aliasMap.containsKey(name);    }    /**     * 返回指定的Bean名称的所有别名     */    @Override    public String[] getAliases(String name) {        List<String> result = new ArrayList<String>();        synchronized (this.aliasMap) {            retrieveAliases(name, result);        }        return StringUtils.toStringArray(result);    }    /**     * 递归检索指定的Bean的所有别名     */    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);            }        }    }    /**     * 根据StringValueResolver解析为对应的别名     */    public void resolveAliases(StringValueResolver valueResolver) {        Assert.notNull(valueResolver, "StringValueResolver must not be null");        synchronized (this.aliasMap) {            Map<String, String> aliasCopy = new HashMap<String, String>(this.aliasMap);            for (String alias : aliasCopy.keySet()) {                String registeredName = aliasCopy.get(alias);                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);                }            }        }    }    /**     * 检查给定的名称是否指向别名作为别名（死循环）     */    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");        }    }    /**     * 判断原始名称，解析别名为规范名称     */    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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