SimpleAliasRegistry

public class SimpleAliasRegistry implements AliasRegistry {    protected final Log logger = LogFactory.getLog(getClass());    //别名集合    private final Map<String, String> aliasMap = new ConcurrentHashMap<>(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");        //对别名集合进行同步        synchronized (this.aliasMap) {             //如果别名等于名称，从别名集合中删除别名            if (alias.equals(name)) {                this.aliasMap.remove(alias);                if (logger.isDebugEnabled()) {                    logger.debug("Alias definition '" + alias + "' ignored since it points to same name");                }            }            else {                //判断别名是否注册过                String registeredName = this.aliasMap.get(alias);                //如果给指定的名称注册过相同的别名，就直接返回。                if (registeredName != null) {                    if (registeredName.equals(name)) {                        // An existing alias - no need to re-register                        return;                    }                    //别名是否允许被覆盖                    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 + "'");                    }                }                //循环检测                checkForAliasCircle(name, alias);                //注册别名                this.aliasMap.put(alias, name);                if (logger.isTraceEnabled()) {                    logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");                }            }        }    }    /**     * 返回别名是否允许覆盖     */    protected boolean allowAliasOverriding() {        return true;    }    /**     * 判断给定的名称是否已经注册给定的别名     */    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();                if (registeredAlias.equals(alias) || hasAlias(registeredAlias, alias)) {                    return true;                }            }        }        return false;    }    /**     * 移除别名     */    @Override    public void removeAlias(String alias) {        //对别名集合进行同步        synchronized (this.aliasMap) {            String name = this.aliasMap.remove(alias);            if (name == null) {                throw new IllegalStateException("No alias '" + alias + "' registered");            }        }    }    /**     * 判断给定的名称是否是别名     */    @Override    public boolean isAlias(String name) {        return this.aliasMap.containsKey(name);    }    /**     * 获取给定名称的所有别名     */    @Override    public String[] getAliases(String name) {        List<String> result = new ArrayList<>();        synchronized (this.aliasMap) {            retrieveAliases(name, result);        }        return StringUtils.toStringArray(result);    }    /**     * 获得给定名称的所有别名     */    private void retrieveAliases(String name, List<String> result) {        this.aliasMap.forEach((alias, registeredName) -> {            if (registeredName.equals(name)) {                result.add(alias);                retrieveAliases(alias, result);            }        });    }    /**     *     */    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);                }            });        }    }    /**     *     */    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");        }    }    /**     *     */    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;    }}