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Dubbo源码解读5-扩展点类ExtensionLoader getActivateExtension方法

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逻辑解析

根据Activate注解来进行扩展点实现类排序实例对象，使用TreeMap来进行扩展点类进行排序保存，排序类为ActivateComparator

相关代码

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public List<T> getActivateExtension(URL url, String key, String group) {
    String value = url.getParameter(key);
    return getActivateExtension(url, StringUtils.isEmpty(value) ? null : COMMA_SPLIT_PATTERN.split(value), group);
}
public List<T> getActivateExtension(URL url, String[] values, String group) {
    List<T> activateExtensions = new ArrayList<>();
    // solve the bug of using @SPI's wrapper method to report a null pointer exception.
    TreeMap<Class, T> activateExtensionsMap = new TreeMap<>(ActivateComparator.COMPARATOR);
    Set<String> loadedNames = new HashSet<>();
    Set<String> names = CollectionUtils.ofSet(values);
    if (!names.contains(REMOVE_VALUE_PREFIX + DEFAULT_KEY)) {
        getExtensionClasses();
        for (Map.Entry<String, Object> entry : cachedActivates.entrySet()) {
            String name = entry.getKey();
            Object activate = entry.getValue();
            String[] activateGroup, activateValue;
            if (activate instanceof Activate) {
                activateGroup = ((Activate) activate).group();
                activateValue = ((Activate) activate).value();
            } else if (activate instanceof com.alibaba.dubbo.common.extension.Activate) {
                activateGroup = ((com.alibaba.dubbo.common.extension.Activate) activate).group();
                activateValue = ((com.alibaba.dubbo.common.extension.Activate) activate).value();
            } else {
                continue;
            }
            if (isMatchGroup(group, activateGroup)
                    && !names.contains(name)
                    && !names.contains(REMOVE_VALUE_PREFIX + name)
                    && isActive(activateValue, url)
                    && !loadedNames.contains(name)) {
                activateExtensionsMap.put(getExtensionClass(name), getExtension(name));
                loadedNames.add(name);
            }
        }
        if (!activateExtensionsMap.isEmpty()) {
            activateExtensions.addAll(activateExtensionsMap.values());
        }
    }
    List<T> loadedExtensions = new ArrayList<>();
    for (String name : names) {
        if (!name.startsWith(REMOVE_VALUE_PREFIX)
                && !names.contains(REMOVE_VALUE_PREFIX + name)) {
            if (!loadedNames.contains(name)) {
                if (DEFAULT_KEY.equals(name)) {
                    if (!loadedExtensions.isEmpty()) {
                        activateExtensions.addAll(0, loadedExtensions);
                        loadedExtensions.clear();
                    }
                } else {
                    loadedExtensions.add(getExtension(name));
                }
                loadedNames.add(name);
            } else {
                // If getExtension(name) exists, getExtensionClass(name) must exist, so there is no null pointer processing here.
                String simpleName = getExtensionClass(name).getSimpleName();
                logger.warn("Catch duplicated filter, ExtensionLoader will ignore one of them. Please check. Filter Name: " + name +
                        ". Ignored Class Name: " + simpleName);
            }
        }
    }
    if (!loadedExtensions.isEmpty()) {
        activateExtensions.addAll(loadedExtensions);
    }
    return activateExtensions;
}