每个ExtensionLoader实例只负责加载一个特定扩大点实现
每个扩大点对应最多只有一个ExtensionLoader实例
对于每个扩大点实现，最多只会有一个实例
一个扩大点实现能够对应多个名称(逗号分隔)
每个扩大点最多只能有一个被AdaptiveExtension
每个扩大点能够有多个可主动激活的扩大点实现(应用@Activate注解)
因为每个扩大点实现最多只有一个实例，因而扩大点实现应保障线程平安
如果扩大点有多个Wrapper，那么最终其执行的程序不确定(外部应用ConcurrentHashSet存储)
getExtension办法：
public T getExtension(String name) { if (name == null || name.length() == 0) throw new IllegalArgumentException("Extension name == null"); if ("true".equals(name)) { return getDefaultExtension(); } // 先从缓存获取 Holder<Object> holder = cachedInstances.get(name); if (holder == null) { cachedInstances.putIfAbsent(name, new Holder<Object>()); holder = cachedInstances.get(name); } Object instance = holder.get(); if (instance == null) { synchronized (holder) { instance = holder.get(); if (instance == null) { // 构建instance instance = createExtension(name); holder.set(instance); } } } return (T) instance;}createExtension办法：
private T createExtension(String name) { // 获取class文件 Class<?> clazz = getExtensionClasses().get(name); if (clazz == null) { throw findException(name); } try { // 线程缓存获取 T instance = (T) EXTENSION_INSTANCES.get(clazz); if (instance == null) { // 反射构建对象 EXTENSION_INSTANCES.putIfAbsent(clazz, clazz.newInstance()); instance = (T) EXTENSION_INSTANCES.get(clazz); } // IOC填充对象 injectExtension(instance); Set<Class<?>> wrapperClasses = cachedWrapperClasses; // AOP切片实现 if (wrapperClasses != null && !wrapperClasses.isEmpty()) { // 通过含参的构造方法将SPI实例（依据指定名字创立好的）注入进去 // 注入胜利并创立好实例之后会把这个组装好的Wrapper实例返回 // 这样循环到下一个Wrapper类时其实注入的是上一个Wrapper类实例 // 这样导致先注入的后执行 for (Class<?> wrapperClass : wrapperClasses) { instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance)); } } // 返回构建好的实力 return instance; } catch (Throwable t) { throw new IllegalStateException("Extension instance(name: " + name + ", class: " + type + ") could not be instantiated: " + t.getMessage(), t); }}injectExtension办法：
private T injectExtension(T instance) { try { if (objectFactory != null) { // 遍历指标类上的所有办法 for (Method method : instance.getClass().getMethods()) { // 查看办法是否已set 结尾，且办法只有一个参数，且办法拜访级别是public if (method.getName().startsWith("set") && method.getParameterTypes().length == 1 && Modifier.isPublic(method.getModifiers())) { /** * Check {@link DisableInject} to see if we need auto injection for this property */ // 如果办法有 DisableInject 注解润饰，则疏忽 if (method.getAnnotation(DisableInject.class) != null) { continue; } // 获取 setter 办法参数类型 Class<?> pt = method.getParameterTypes()[0]; if (ReflectUtils.isPrimitives(pt)) { continue; } try { // 获取属性名，比方 setName 办法对应属性名 name String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : ""; // 从 ObjectFactory 中获取依赖对象 Object object = objectFactory.getExtension(pt, property); if (object != null) { // 通过反射调用 setter 办法设置依赖 method.invoke(instance, object); } } catch (Exception e) { logger.error("Failed to inject via method " + method.getName() + " of interface " + type.getName() + ": " + e.getMessage(), e); } } } } } catch (Exception e) { logger.error(e.getMessage(), e); } return instance;}getExtensionClasses办法：
private Map<String, Class<?>> getExtensionClasses() { Map<String, Class<?>> classes = cachedClasses.get(); // 先从缓存获取，没有就去加载 if (classes == null) { synchronized (cachedClasses) { classes = cachedClasses.get(); if (classes == null) { classes = loadExtensionClasses(); cachedClasses.set(classes); } } } return classes;}loadExtensionClasses办法：
private Map<String, Class<?>> loadExtensionClasses() { // 加载默认的实现 final SPI defaultAnnotation = type.getAnnotation(SPI.class); if (defaultAnnotation != null) { String value = defaultAnnotation.value(); if ((value = value.trim()).length() > 0) { String[] names = NAME_SEPARATOR.split(value); // 默认实现只能一个 if (names.length > 1) { throw new IllegalStateException("more than 1 default extension name on extension " + type.getName() + ": " + Arrays.toString(names)); } if (names.length == 1) cachedDefaultName = names[0]; } } // 从META-INF/dubbo/internal/、META-INF/dubbo/、META-INF/services/ 这三个指定的文件夹加加载此类型的实现类 Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>(); loadDirectory(extensionClasses, DUBBO_INTERNAL_DIRECTORY); loadDirectory(extensionClasses, DUBBO_DIRECTORY); loadDirectory(extensionClasses, SERVICES_DIRECTORY); return extensionClasses;}loadDirectory办法：
private void loadDirectory(Map<String, Class<?>> extensionClasses, String dir) { String fileName = dir + type.getName(); try { Enumeration<java.net.URL> urls; ClassLoader classLoader = findClassLoader(); // 依据文件名加载所有的同名文件 if (classLoader != null) { urls = classLoader.getResources(fileName); } else { urls = ClassLoader.getSystemResources(fileName); } if (urls != null) { while (urls.hasMoreElements()) { java.net.URL resourceURL = urls.nextElement(); // 加载文件里的资源 loadResource(extensionClasses, classLoader, resourceURL); } } } catch (Throwable t) { logger.error("Exception when load extension class(interface: " + type + ", description file: " + fileName + ").", t); }}loadResource办法：
private void loadResource(Map<String, Class<?>> extensionClasses, ClassLoader classLoader, java.net.URL resourceURL) { try { BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), "utf-8")); try { String line; while ((line = reader.readLine()) != null) { final int ci = line.indexOf('#'); if (ci >= 0) line = line.substring(0, ci); line = line.trim(); if (line.length() > 0) { try { String name = null; // 依据 = 宰割 int i = line.indexOf('='); if (i > 0) { name = line.substring(0, i).trim(); line = line.substring(i + 1).trim(); } if (line.length() > 0) { // 依据读取的内容 应用Class.forName加载对应类 loadClass(extensionClasses, resourceURL, Class.forName(line, true, classLoader), name); } } catch (Throwable t) { IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: " + type + ", class line: " + line + ") in " + resourceURL + ", cause: " + t.getMessage(), t); exceptions.put(line, e); } } } } finally { reader.close(); } } catch (Throwable t) { logger.error("Exception when load extension class(interface: " + type + ", class file: " + resourceURL + ") in " + resourceURL, t); }}loadClass办法：
private void loadClass(Map<String, Class<?>> extensionClasses, java.net.URL resourceURL, Class<?> clazz, String name) throws NoSuchMethodException { if (!type.isAssignableFrom(clazz)) { throw new IllegalStateException("Error when load extension class(interface: " + type + ", class line: " + clazz.getName() + "), class " + clazz.getName() + "is not subtype of interface."); } if (clazz.isAnnotationPresent(Adaptive.class)) { if (cachedAdaptiveClass == null) { // 如果类被Adaptive润饰，设置cachedAdaptiveClass缓存 cachedAdaptiveClass = clazz; } else if (!cachedAdaptiveClass.equals(clazz)) { throw new IllegalStateException("More than 1 adaptive class found: " + cachedAdaptiveClass.getClass().getName() + ", " + clazz.getClass().getName()); } } else if (isWrapperClass(clazz)) { // 如果是wrapper类，设置wrapper的缓存 Set<Class<?>> wrappers = cachedWrapperClasses; if (wrappers == null) { cachedWrapperClasses = new ConcurrentHashSet<Class<?>>(); wrappers = cachedWrapperClasses; } wrappers.add(clazz); } else { // 一般的spi实现类 clazz.getConstructor(); if (name == null || name.length() == 0) { name = findAnnotationName(clazz); if (name.length() == 0) { throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + resourceURL); } } String[] names = NAME_SEPARATOR.split(name); if (names != null && names.length > 0) { Activate activate = clazz.getAnnotation(Activate.class); if (activate != null) { //如果有activate 退出缓存 如果对应多个名字 只会采纳第一个名字 cachedActivates.put(names[0], activate); } for (String n : names) { if (!cachedNames.containsKey(clazz)) { cachedNames.put(clazz, n); } Class<?> c = extensionClasses.get(n); if (c == null) { // 将名字->类退出缓存 extensionClasses.put(n, clazz); } else if (c != clazz) { throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName()); } } } }}///
///
getAdaptiveExtension办法：
public T getAdaptiveExtension() { Object instance = cachedAdaptiveInstance.get(); // 双重查看 加锁创立缓存 if (instance == null) { if (createAdaptiveInstanceError == null) { synchronized (cachedAdaptiveInstance) { instance = cachedAdaptiveInstance.get(); if (instance == null) { try { // 缓存没有 创立 instance = createAdaptiveExtension(); cachedAdaptiveInstance.set(instance); } catch (Throwable t) { createAdaptiveInstanceError = t; throw new IllegalStateException("fail to create adaptive instance: " + t.toString(), t); } } } } else { throw new IllegalStateException("fail to create adaptive instance: " + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError); } } return (T) instance;}createAdaptiveExtension办法：
// 调用 getAdaptiveExtensionClass 办法获取自适应拓展 Class 对象 // 通过反射进行实例化 // 调用injectExtension办法向拓展实例中注入依赖 private T createAdaptiveExtension() { try { return injectExtension((T) getAdaptiveExtensionClass().newInstance()); } catch (Exception e) { throw new IllegalStateException("Can not create adaptive extension " + type + ", cause: " + e.getMessage(), e); }}getAdaptiveExtensionClass办法：
private Class<?> getAdaptiveExtensionClass() { // 先获取此type的所有实现类的class getExtensionClasses(); if (cachedAdaptiveClass != null) { //如果有 Adaptive润饰的实现类 间接返回 return cachedAdaptiveClass; } // 构建代理类 return cachedAdaptiveClass = createAdaptiveExtensionClass();}createAdaptiveExtensionClass办法：
private Class<?> createAdaptiveExtensionClass() { // 生成代理类的代码 String code = createAdaptiveExtensionClassCode(); ClassLoader classLoader = findClassLoader(); com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension(); // 应用javassist 编译为class return compiler.compile(code, classLoader);}createAdaptiveExtensionClassCode办法：
private String createAdaptiveExtensionClassCode() { StringBuilder codeBuilder = new StringBuilder(); Method[] methods = type.getMethods(); boolean hasAdaptiveAnnotation = false; // 第一局部 // 如果没有Adaptive润饰办法会抛异样 for (Method m : methods) { if (m.isAnnotationPresent(Adaptive.class)) { hasAdaptiveAnnotation = true; break; } } // no need to generate adaptive class since there's no adaptive method found. if (!hasAdaptiveAnnotation) throw new IllegalStateException("No adaptive method on extension " + type.getName() + ", refuse to create the adaptive class!"); // 第二局部 // 生成package、import等代码 codeBuilder.append("package ").append(type.getPackage().getName()).append(";"); codeBuilder.append("\nimport ").append(ExtensionLoader.class.getName()).append(";"); codeBuilder.append("\npublic class ").append(type.getSimpleName()).append("$Adaptive").append(" implements ").append(type.getCanonicalName()).append(" {"); //第三局部 // 如果Adaptive没有润饰办法，此代理类不会构建具体的办法 // Adaptive润饰的办法必须参数含有URL或者某个参数有getURL办法 for (Method method : methods) { Class<?> rt = method.getReturnType(); Class<?>[] pts = method.getParameterTypes(); Class<?>[] ets = method.getExceptionTypes(); Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class); StringBuilder code = new StringBuilder(512); if (adaptiveAnnotation == null) { code.append("throw new UnsupportedOperationException(\"method ") .append(method.toString()).append(" of interface ") .append(type.getName()).append(" is not adaptive method!\");"); } else { int urlTypeIndex = -1; for (int i = 0; i < pts.length; ++i) { if (pts[i].equals(URL.class)) { urlTypeIndex = i; break; } } // found parameter in URL type if (urlTypeIndex != -1) { // Null Point check String s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"url == null\");", urlTypeIndex); code.append(s); s = String.format("\n%s url = arg%d;", URL.class.getName(), urlTypeIndex); code.append(s); } // did not find parameter in URL type else { String attribMethod = null; // find URL getter method LBL_PTS: for (int i = 0; i < pts.length; ++i) { Method[] ms = pts[i].getMethods(); for (Method m : ms) { String name = m.getName(); if ((name.startsWith("get") || name.length() > 3) && Modifier.isPublic(m.getModifiers()) && !Modifier.isStatic(m.getModifiers()) && m.getParameterTypes().length == 0 && m.getReturnType() == URL.class) { urlTypeIndex = i; attribMethod = name; break LBL_PTS; } } } if (attribMethod == null) { throw new IllegalStateException("fail to create adaptive class for interface " + type.getName() + ": not found url parameter or url attribute in parameters of method " + method.getName()); } // Null point check String s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"%s argument == null\");", urlTypeIndex, pts[urlTypeIndex].getName()); code.append(s); s = String.format("\nif (arg%d.%s() == null) throw new IllegalArgumentException(\"%s argument %s() == null\");", urlTypeIndex, attribMethod, pts[urlTypeIndex].getName(), attribMethod); code.append(s); s = String.format("%s url = arg%d.%s();", URL.class.getName(), urlTypeIndex, attribMethod); code.append(s); } // 第四局部 // 生成类对应的名字 String[] value = adaptiveAnnotation.value(); // value is not set, use the value generated from class name as the key if (value.length == 0) { // 如果注解没有给出名字 就用类名用.拼接 eg: CatST --> cat.s.t char[] charArray = type.getSimpleName().toCharArray(); StringBuilder sb = new StringBuilder(128); for (int i = 0; i < charArray.length; i++) { if (Character.isUpperCase(charArray[i])) { if (i != 0) { sb.append("."); } sb.append(Character.toLowerCase(charArray[i])); } else { sb.append(charArray[i]); } } value = new String[]{sb.toString()}; } // Invocation参数解决 boolean hasInvocation = false; for (int i = 0; i < pts.length; ++i) { if (pts[i].getName().equals("com.alibaba.dubbo.rpc.Invocation")) { // Null Point check String s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"invocation == null\");", i); code.append(s); s = String.format("\nString methodName = arg%d.getMethodName();", i); code.append(s); hasInvocation = true; break; } } String defaultExtName = cachedDefaultName; String getNameCode = null; for (int i = value.length - 1; i >= 0; --i) { if (i == value.length - 1) { if (null != defaultExtName) { if (!"protocol".equals(value[i])) if (hasInvocation) getNameCode = String.format("url.getMethodParameter(methodName, \"%s\", \"%s\")", value[i], defaultExtName); else getNameCode = String.format("url.getParameter(\"%s\", \"%s\")", value[i], defaultExtName); else getNameCode = String.format("( url.getProtocol() == null ? \"%s\" : url.getProtocol() )", defaultExtName); } else { if (!"protocol".equals(value[i])) if (hasInvocation) getNameCode = String.format("url.getMethodParameter(methodName, \"%s\", \"%s\")", value[i], defaultExtName); else getNameCode = String.format("url.getParameter(\"%s\")", value[i]); else getNameCode = "url.getProtocol()"; } } else { if (!"protocol".equals(value[i])) if (hasInvocation) getNameCode = String.format("url.getMethodParameter(methodName, \"%s\", \"%s\")", value[i], defaultExtName); else getNameCode = String.format("url.getParameter(\"%s\", %s)", value[i], getNameCode); else getNameCode = String.format("url.getProtocol() == null ? (%s) : url.getProtocol()", getNameCode); } } code.append("\nString extName = ").append(getNameCode).append(";"); // check extName == null? String s = String.format("\nif(extName == null) " + "throw new IllegalStateException(\"Fail to get extension(%s) name from url(\" + url.toString() + \") use keys(%s)\");", type.getName(), Arrays.toString(value)); code.append(s); s = String.format("\n%s extension = (%<s)%s.getExtensionLoader(%s.class).getExtension(extName);", type.getName(), ExtensionLoader.class.getSimpleName(), type.getName()); code.append(s); // 第五局部 生成返回类型 // return statement if (!rt.equals(void.class)) { code.append("\nreturn "); } // 第六局部 生成拓展加载与指标办法调用逻辑 大抵逻辑就是依据获取到的name获取对应的实现类，而后调用实现类的办法 s = String.format("extension.%s(", method.getName()); code.append(s); for (int i = 0; i < pts.length; i++) { if (i != 0) code.append(", "); code.append("arg").append(i); } code.append(");"); } codeBuilder.append("\npublic ").append(rt.getCanonicalName()).append(" ").append(method.getName()).append("("); for (int i = 0; i < pts.length; i++) { if (i > 0) { codeBuilder.append(", "); } codeBuilder.append(pts[i].getCanonicalName()); codeBuilder.append(" "); codeBuilder.append("arg").append(i); } codeBuilder.append(")"); if (ets.length > 0) { codeBuilder.append(" throws "); for (int i = 0; i < ets.length; i++) { if (i > 0) { codeBuilder.append(", "); } codeBuilder.append(ets[i].getCanonicalName()); } } codeBuilder.append(" {"); codeBuilder.append(code.toString()); codeBuilder.append("\n}"); } codeBuilder.append("\n}"); if (logger.isDebugEnabled()) { logger.debug(codeBuilder.toString()); } return codeBuilder.toString();}///
///
getActivateExtension办法：
public List<T> getActivateExtension(URL url, String[] values, String group) { List<T> exts = new ArrayList<T>(); List<String> names = values == null ? new ArrayList<String>(0) : Arrays.asList(values); if (!names.contains(Constants.REMOVE_VALUE_PREFIX + Constants.DEFAULT_KEY)) { getExtensionClasses(); for (Map.Entry<String, Activate> entry : cachedActivates.entrySet()) { String name = entry.getKey(); Activate activate = entry.getValue(); // 依据group过滤 if (isMatchGroup(group, activate.group())) { T ext = getExtension(name); if (!names.contains(name) // 避免反复退出 上面就是依据指定name寻找对应的实现类 && !names.contains(Constants.REMOVE_VALUE_PREFIX + name) && isActive(activate, url)) { // 检测value和url 如果类上的Activate(value={"bigKey"},group = "q") 制订了value,那么url中如果不含有此key的参数就匹配不上 exts.add(ext); } } } Collections.sort(exts, ActivateComparator.COMPARATOR); } List<T> usrs = new ArrayList<T>(); // 依据name寻找实现类 for (int i = 0; i < names.size(); i++) { String name = names.get(i); if (!name.startsWith(Constants.REMOVE_VALUE_PREFIX) && !names.contains(Constants.REMOVE_VALUE_PREFIX + name)) { if (Constants.DEFAULT_KEY.equals(name)) { if (!usrs.isEmpty()) { exts.addAll(0, usrs); usrs.clear(); } } else { T ext = getExtension(name); usrs.add(ext); } } } if (!usrs.isEmpty()) { exts.addAll(usrs); } return exts;}////https://www.jianshu.com/u/ee989c623747https://blog.csdn.net/yuansha...
https://blog.csdn.net/qq_3521...