作用

配置工厂ConfigurationFactory是用于加载用户的配置文件的，配置文件是怎么获取的？这篇文章就是讲的通过ConfigurationFactory去获取配置文件的过程。

实例

• ConfigurationFactory在类初始化的时候, 通过饿汉式模式创建单实例。Factory是其静态内部子类

private static ConfigurationFactory configFactory = new Factory();

private static class Factory extends ConfigurationFactory {
//省略部分代码
}

• ConfigurationFactory通过getInstance方法获取其实例。

初始化

设计模式

在getInstance方法中进行初始化，双检锁模式保证只被初始化一次

private static volatile List<ConfigurationFactory> factories = null;
    private static final Lock LOCK = new ReentrantLock();

	public static ConfigurationFactory getInstance() {
        if (factories == null) {
            LOCK.lock();
            try {
            	if (factories == null) {
               		//省略部分代码以说明双检锁模式
                }
            } finally {
                LOCK.unlock();
            }
        }
        return configFactory;
    }

初始化流程图

代码解析

• 自定义配置工厂类需要设置属性log4j.configurationFactory即可, 代码如下：

final String factoryClass = PropertiesUtil.getProperties().getStringProperty(CONFIGURATION_FACTORY_PROPERTY);
    if (factoryClass != null) {
        addFactory(list, factoryClass);
    }

• 获取内置配置工厂类并加入配置工厂列表

//获取插件
	//CATEGORY的值为ConfiguratioFactory
	final PluginManager manager = new PluginManager(CATEGORY);
    manager.collectPlugins();
    final Map<String, PluginType<?>> plugins = manager.getPlugins();
    
    //对内置加载的类进行类型检查并加入到未排序列表
    final List<Class<? extends ConfigurationFactory>> ordered = new ArrayList<>(plugins.size());
    for (final PluginType<?> type : plugins.values()) {
        try {
            ordered.add(type.getPluginClass().asSubclass(ConfigurationFactory.class));
        } catch (final Exception ex) {
            LOGGER.warn("Unable to add class {}", type.getPluginClass(), ex);
        }
    }
    
    //按照OrderComparator定义的顺序进行加载
    Collections.sort(ordered, OrderComparator.getInstance());
    for (final Class<? extends ConfigurationFactory> clazz : ordered) {
        addFactory(list, clazz);
    }
    //转变成unmodified的list
    factories = Collections.unmodifiableList(list);

• PluginManager收集插件的方法解析

说明：

• 如果不了解OSGI可以看看这篇文章
• ConfigurationFactory初始化过程中，packages被指定为null
• OrdeComparator，优先级比较器

public int compare(final Class<?> lhs, final Class<?> rhs) {
        final Order lhsOrder = Objects.requireNonNull(lhs, "lhs").getAnnotation(Order.class);
        final Order rhsOrder = Objects.requireNonNull(rhs, "rhs").getAnnotation(Order.class);
        if (lhsOrder == null && rhsOrder == null) {
            return 0;
        }
        //有@Order注解的优先级高
        if (rhsOrder == null) {
            return -1;
        }
        //有@Order注解的优先级高
        if (lhsOrder == null) {
            return 1;
        }
        //@Order注解的值越大，优先级越高
        return Integer.signum(rhsOrder.value() - lhsOrder.value());
    }

举个例子：
JsonConfigurationFacotory的Order值是6，YamlConfigurationFactory的Order值是7，那么YamlConfigurationFactory应该排在JsonConfigurationFacotory之前。内置一共四个解析插件，他们的排序是:

• PropertiesConfigurationFactory (8)
• YamlConfigurationFactory (7)
• JsonConfigurationFacotory (6)
• XmlConfigurationFactory (5)