feat: SPI 自适应拓展分析

xiaochangbai · Dec 20, 2021 · ad2b60f · ad2b60f
1 parent 7727611
commit ad2b60f
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diff --git a/dubbo-common/src/main/java/org/apache/dubbo/common/extension/AdaptiveClassCodeGenerator.java b/dubbo-common/src/main/java/org/apache/dubbo/common/extension/AdaptiveClassCodeGenerator.java
@@ -218,9 +218,11 @@ private String generateUrlNullCheck(int index) {
     private String generateMethodContent(Method method) {
         Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class);
         StringBuilder code = new StringBuilder(512);
+        // 如果方法上无 Adaptive 注解，则生成 throw new UnsupportedOperationException(...) 代码
         if (adaptiveAnnotation == null) {
             return generateUnsupported(method);
         } else {
+            // 遍历参数列表，确定 URL 参数位置
             int urlTypeIndex = getUrlTypeIndex(method);
 
             // found parameter in URL type
@@ -374,6 +376,11 @@ private String generateUrlAssignmentIndirectly(Method method) {
         for (int i = 0; i < pts.length; ++i) {
             for (Method m : pts[i].getMethods()) {
                 String name = m.getName();
+                // 1. 方法名以 get 开头，或方法名大于3个字符
+                // 2. 方法的访问权限为 public
+                // 3. 非静态方法
+                // 4. 方法参数数量为0
+                // 5. 方法返回值类型为 URL
                 if ((name.startsWith("get") || name.length() > 3)
                         && Modifier.isPublic(m.getModifiers())
                         && !Modifier.isStatic(m.getModifiers())

diff --git a/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java b/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java
@@ -702,6 +702,7 @@ public void replaceExtension(String name, Class<?> clazz) {
     @SuppressWarnings("unchecked")
     public T getAdaptiveExtension() {
         checkDestroyed();
+        // 从缓存中获取自适应拓展
         Object instance = cachedAdaptiveInstance.get();
         if (instance == null) {
             if (createAdaptiveInstanceError != null) {
@@ -714,7 +715,9 @@ public T getAdaptiveExtension() {
                 instance = cachedAdaptiveInstance.get();
                 if (instance == null) {
                     try {
+                        // 创建自适应拓展
                         instance = createAdaptiveExtension();
+                        // 设置自适应拓展到缓存中
                         cachedAdaptiveInstance.set(instance);
                     } catch (Throwable t) {
                         createAdaptiveInstanceError = t;
@@ -1255,8 +1258,10 @@ private String findAnnotationName(Class<?> clazz) {
     @SuppressWarnings("unchecked")
     private T createAdaptiveExtension() {
         try {
+            // 获取自适应拓展类，并通过反射实例化
             T instance = (T) getAdaptiveExtensionClass().newInstance();
             instance = postProcessBeforeInitialization(instance, null);
+            //注入依赖
             instance = injectExtension(instance);
             instance = postProcessAfterInitialization(instance, null);
             initExtension(instance);
@@ -1267,10 +1272,12 @@ private T createAdaptiveExtension() {
     }
 
     private Class<?> getAdaptiveExtensionClass() {
+        // 通过 SPI 获取所有的拓展类
         getExtensionClasses();
         if (cachedAdaptiveClass != null) {
             return cachedAdaptiveClass;
         }
+        // 创建自适应拓展类
         return cachedAdaptiveClass = createAdaptiveExtensionClass();
     }
 
@@ -1284,9 +1291,12 @@ private Class<?> createAdaptiveExtensionClass() {
         } catch (Throwable ignore) {
 
         }
+        // 构建自适应拓展代码
         String code = new AdaptiveClassCodeGenerator(type, cachedDefaultName).generate();
+        // 获取编译器实现类
         org.apache.dubbo.common.compiler.Compiler compiler = extensionDirector.getExtensionLoader(
             org.apache.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
+        // 编译代码，生成 Class
         return compiler.compile(code, classLoader);
     }