Dubbo-加载初始化

刺骨的言语ヽ痛彻心扉 2022-01-28 16:19 309阅读 0赞

**首先我们在SpringBoot的yaml文件中会有如下配置：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1lhbmd6YWlMZUhlSGU_size_16_color_FFFFFF_t_70][]

上面配置的是dubbo使用的协议，由于dubbo建议我们使用dubbo协议，所以配置如上。

Springboot加载的时候回读取yam文件，然后找到具体的实现类这时会用到ExtensionLoader<T> getExtensionLoader(Class<T> type) 方法。

加载第一步：

如下图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1lhbmd6YWlMZUhlSGU_size_16_color_FFFFFF_t_70 1][]

加载第一步会传入上图中的type 接口类型，因为是第一次加载所以loader为空我们发现会创建ExtensionLoader对象。

public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
            if (type == null) {
                throw new IllegalArgumentException("Extension type == null");
            } else if (!type.isInterface()) {
                throw new IllegalArgumentException("Extension type(" + type + ") is not interface!");
            } else if (!withExtensionAnnotation(type)) {
                throw new IllegalArgumentException("Extension type(" + type + ") is not extension, because WITHOUT @" + SPI.class.getSimpleName() + " Annotation!");
            } else {
                ExtensionLoader<T> loader = (ExtensionLoader)EXTENSION_LOADERS.get(type);
                if (loader == null) {
                    EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader(type));
                    loader = (ExtensionLoader)EXTENSION_LOADERS.get(type);
                }
    
                return loader;
            }
        }

看一下ExtensionLoader的构造方法：

private ExtensionLoader(Class<?> type) {
            this.type = type;
            this.objectFactory = type == ExtensionFactory.class ? null : (ExtensionFactory)getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension();
        }

因为传入的不是ExtensionFactory 类所以会走三元运算符的后半部分，再次调用getExtensionLoader方法，传入ExtensionFactory类，紧接着再一次调用构造函数因为类型为ExtensionFactory 所以返回空，然后执行上一步返回，开始调用getAdaptiveExtension()方法，因为此时返回的loader对象中是ExtensionFactory对象，此时方法的下图部分执行完毕：

this.objectFactory = type == ExtensionFactory.class ? null : (ExtensionFactory)getExtensionLoader(ExtensionFactory.class)

![20190524114431504.jpg][]

然后开始执行getAdaptiveExtension()方法。

然后我们注意getAdaptiveExtension()方法中的下一行代码：

instance = this.createAdaptiveExtension();

跟进去：

private T createAdaptiveExtension() {
            try {
                return this.injectExtension(this.getAdaptiveExtensionClass().newInstance());
            } catch (Exception var2) {
                throw new IllegalStateException("Can not create adaptive extension " + this.type + ", cause: " + var2.getMessage(), var2);
            }
        }

注意下面，开始获取自适应拓展进行加载。

return this.injectExtension(this.getAdaptiveExtensionClass().newInstance());

private Class<?> getAdaptiveExtensionClass() {
            this.getExtensionClasses();
            return this.cachedAdaptiveClass != null ? this.cachedAdaptiveClass : (this.cachedAdaptiveClass = this.createAdaptiveExtensionClass());
        }

我们注意：this.getExtensionClasses();这个是加载扩展点的实现类了。

classes = this.loadExtensionClasses()

里面在关注loadExtensionClasses（ ）方法。去指定目录下加载文件。

private Map<String, Class<?>> loadExtensionClasses() {
            SPI defaultAnnotation = (SPI)this.type.getAnnotation(SPI.class);
            if (defaultAnnotation != null) {
                String value = defaultAnnotation.value();
                if (value != null && (value = value.trim()).length() > 0) {
                    String[] names = NAME_SEPARATOR.split(value);
                    if (names.length > 1) {
                        throw new IllegalStateException("more than 1 default extension name on extension " + this.type.getName() + ": " + Arrays.toString(names));
                    }
    
                    if (names.length == 1) {
                        this.cachedDefaultName = names[0];
                    }
                }
            }
    
            Map<String, Class<?>> extensionClasses = new HashMap();
            this.loadFile(extensionClasses, "META-INF/dubbo/internal/");
            this.loadFile(extensionClasses, "META-INF/dubbo/");
            this.loadFile(extensionClasses, "META-INF/services/");
            return extensionClasses;
        }

然后创建自适应扩展类，

@Adaptive
    public class AdaptiveExtensionFactory implements ExtensionFactory {
        private final List<ExtensionFactory> factories;
    
        public AdaptiveExtensionFactory() {
            ExtensionLoader<ExtensionFactory> loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class);
            List<ExtensionFactory> list = new ArrayList();
            Iterator i$ = loader.getSupportedExtensions().iterator();
    
            while(i$.hasNext()) {
                String name = (String)i$.next();
                list.add(loader.getExtension(name));
            }
    
            this.factories = Collections.unmodifiableList(list);
        }
    
        public <T> T getExtension(Class<T> type, String name) {
            Iterator i$ = this.factories.iterator();
    
            Object extension;
            do {
                if (!i$.hasNext()) {
                    return null;
                }
    
                ExtensionFactory factory = (ExtensionFactory)i$.next();
                extension = factory.getExtension(type, name);
            } while(extension == null);
    
            return extension;
        }
    }

将加载到的SpringExtensionFactory 和 SpiExtensionFactory 注入到 factories中。

![20190524142058322.png][]

然后ExtensionLoader 中的private final ExtensionFactory objectFactory;有了值如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1lhbmd6YWlMZUhlSGU_size_16_color_FFFFFF_t_70 2][]

objectFactory中持有的是AdaptiveExtensionFactory的对象该对象的属性factories 是SpringExtensionFactory 和 SpiExtensionFactory 他们是ExtensionFactory 的两个实现类。AdaptiveExtensionFactory是使用的代理模式。

objectFactory是一个 ExtensionFactory，用来获取所有的托管bean

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1lhbmd6YWlMZUhlSGU_size_16_color_FFFFFF_t_70 1]: /images/20220128/7920b50984b04661ab04e4b945ae1e9d.png
[20190524114431504.jpg]: /images/20220128/3213e4664a104fe18183a95d96cee0ea.png
[20190524142058322.png]: /images/20220128/35b18c896a6e4a2f9e8622075da2924c.png
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