Dubbo源码学习（四、ExtensionLoader 扩展点加载机制,Protocol$Adaptive,ProxyFactory$Adaptive,Cluster$Adaptive）

坚持一下，把源码看完，勤奋一点，不要在懒惰了，你已经落下别人很多了

环境配置:

jdk  1.7.0.17
dubbo 2.5.x
myeclipse 2014
idea 2017

SPI注解的接口

在dubbo中，采用了类似于java的spi机制进行扩展类加载

在dubbo.jar文件夹下有个META-INF/dubbo/internal文件夹下，定义了很多了扩展点加载类,如下图

这些文件名基本是类的全路径名，所有扩展类交由ExtensionLoader来统计进行加载处理

ExtensionLoader的属性和方法

private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);

    private static final String SERVICES_DIRECTORY = "META-INF/services/";
    private static final String DUBBO_DIRECTORY = "META-INF/dubbo/";
    private static final String DUBBO_INTERNAL_DIRECTORY = DUBBO_DIRECTORY + "internal/";

    private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");

    private static final ConcurrentMap, ExtensionLoader> EXTENSION_LOADERS = new ConcurrentHashMap, ExtensionLoader>();

    private static final ConcurrentMap, Object> EXTENSION_INSTANCES = new ConcurrentHashMap, Object>();

    // ==============================

    private final Class type;

    private final ExtensionFactory objectFactory;

    private final ConcurrentMap, String> cachedNames = new ConcurrentHashMap, String>();

    private final Holder>> cachedClasses = new Holder>>();

    private final Map cachedActivates = new ConcurrentHashMap();
    private final ConcurrentMap> cachedInstances = new ConcurrentHashMap>();
    private final Holder