doc: Spring Conditional

Author: huifer

README.md

@@ -68,6 +68,7 @@
 * [Spring-定时任务](/docs/Spring/clazz/Spring-Scheduling.md)
 * [Spring StopWatch](/docs/Spring/clazz/Spring-StopWatch.md)
 * [Spring 元数据](/docs/Spring/clazz/Spring-Metadata.md)
+* [Spring 条件接口](/docs/Spring/clazz/Spring-Conditional.md)
 
 
 ### Spring5 新特性

docs/Spring/clazz/Spring-Conditional.md

@@ -0,0 +1,301 @@
+# Spring Conditional
+- Author: [HuiFer](https://github.com/huifer)
+- 源码阅读仓库: [SourceHot-spring](https://github.com/SourceHot/spring-framework-read)
+
+
+
+## Conditional
+
+```java
+@Target({ ElementType.TYPE, ElementType.METHOD })
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface Conditional {
+
+    /**
+     * 多个匹配器接口
+     */
+    Class<? extends Condition>[] value();
+
+}
+```
+
+
+
+## Condition
+
+```
+@FunctionalInterface
+public interface Condition {
+
+    /**
+     * 匹配,如果匹配返回true进行初始化,返回false跳过初始化
+     */
+    boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
+
+}
+```
+
+
+
+- ConditionContext 上下文
+- AnnotatedTypeMetadata 注解信息
+
+### ConditionContext
+
+```
+public interface ConditionContext {
+
+   /**
+     * bean的定义
+    */
+   BeanDefinitionRegistry getRegistry();
+
+   /**
+     * bean 工厂
+    */
+   @Nullable
+   ConfigurableListableBeanFactory getBeanFactory();
+
+   /**
+     * 环境
+    */
+   Environment getEnvironment();
+
+   /**
+     * 资源加载器
+    */
+   ResourceLoader getResourceLoader();
+
+   /**
+     * 类加载器
+    */
+   @Nullable
+   ClassLoader getClassLoader();
+
+}
+```
+
+- 唯一实现 : `org.springframework.context.annotation.ConditionEvaluator.ConditionContextImpl`
+
+
+
+- 构造方法
+
+```java
+public ConditionContextImpl(@Nullable BeanDefinitionRegistry registry,
+      @Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {
+
+   this.registry = registry;
+   this.beanFactory = deduceBeanFactory(registry);
+   this.environment = (environment != null ? environment : deduceEnvironment(registry));
+   this.resourceLoader = (resourceLoader != null ? resourceLoader : deduceResourceLoader(registry));
+   this.classLoader = deduceClassLoader(resourceLoader, this.beanFactory);
+}
+```
+
+- 在构造方法中加载了一些变量, 这些变量是根据一定规则转换后得到. 具体规则不展开.
+
+
+
+
+
+
+
+### AnnotatedTypeMetadata 
+
+- 元数据接口
+
+```java
+public interface AnnotatedTypeMetadata {
+
+    /**
+     * 获取所有注解
+     */
+    MergedAnnotations getAnnotations();
+
+    /**
+     * 是否有注解
+     */
+    default boolean isAnnotated(String annotationName) {
+        return getAnnotations().isPresent(annotationName);
+    }
+
+    /**
+     * 获取注解的属性
+     */
+    @Nullable
+    default Map<String, Object> getAnnotationAttributes(String annotationName) {
+        return getAnnotationAttributes(annotationName, false);
+    }
+
+}
+```
+
+
+
+
+
+## 源码分析
+
+- 对应测试类`org.springframework.context.annotation.ConfigurationClassWithConditionTests`
+
+```java
+@Test
+public void conditionalOnMissingBeanMatch() throws Exception {
+   AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+   ctx.register(BeanOneConfiguration.class, BeanTwoConfiguration.class);
+   ctx.refresh();
+   assertThat(ctx.containsBean("bean1")).isTrue();
+   assertThat(ctx.containsBean("bean2")).isFalse();
+   assertThat(ctx.containsBean("configurationClassWithConditionTests.BeanTwoConfiguration")).isFalse();
+}
+
+
+
+	@Configuration
+	static class BeanOneConfiguration {
+
+		@Bean
+		public ExampleBean bean1() {
+			return new ExampleBean();
+		}
+	}
+
+	@Configuration
+	@Conditional(NoBeanOneCondition.class)
+	static class BeanTwoConfiguration {
+
+		@Bean
+		public ExampleBean bean2() {
+			return new ExampleBean();
+		}
+	}
+
+
+	static class NoBeanOneCondition implements Condition {
+
+		@Override
+		public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
+			return !context.getBeanFactory().containsBeanDefinition("bean1");
+		}
+	}
+
+```
+
+
+
+
+
+
+
+- `org.springframework.context.annotation.AnnotatedBeanDefinitionReader#doRegisterBean`
+
+
+
+
+
+
+
+
+
+### shouldSkip
+
+
+
+```java
+public boolean shouldSkip(@Nullable AnnotatedTypeMetadata metadata, @Nullable ConfigurationPhase phase) {
+   if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
+      return false;
+   }
+
+   if (phase == null) {
+      if (metadata instanceof AnnotationMetadata &&
+            ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
+         return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
+      }
+      return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
+   }
+
+   List<Condition> conditions = new ArrayList<>();
+   // 获取注解 Conditional 的属性值
+   for (String[] conditionClasses : getConditionClasses(metadata)) {
+      for (String conditionClass : conditionClasses) {
+         // 序列化成注解
+         Condition condition = getCondition(conditionClass, this.context.getClassLoader());
+         // 插入注解列表
+         conditions.add(condition);
+      }
+   }
+
+   AnnotationAwareOrderComparator.sort(conditions);
+
+   for (Condition condition : conditions) {
+      ConfigurationPhase requiredPhase = null;
+      if (condition instanceof ConfigurationCondition) {
+         requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
+      }
+
+      // matches 进行验证
+      if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) {
+         return true;
+      }
+   }
+
+   return false;
+}
+```
+
+
+
+
+
+- 读取注解信息, 并且执行注解对应的类的方法
+
+  用例如下. 实例化`BeanTwoConfiguration`对象的时候会去执行`NoBeanOneCondition`方法
+
+  ```java
+  @Configuration
+  @Conditional(NoBeanOneCondition.class)
+  static class BeanTwoConfiguration {
+  
+     @Bean
+     public ExampleBean bean2() {
+        return new ExampleBean();
+     }
+  }
+  
+  
+  static class NoBeanOneCondition implements Condition {
+  
+  		@Override
+  		public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
+  			return !context.getBeanFactory().containsBeanDefinition("bean1");
+  		}
+  	}
+  ```
+
+ 在开发中可以自定义matches规则
+
+
+
+
+
+
+
+这也是在注册的时候第一个方法
+
+```java
+private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
+      @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
+      @Nullable BeanDefinitionCustomizer[] customizers) {
+
+   AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
+   // 和条件注解相关的函数
+   if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
+      return;
+   }
+ 
+    // 省略其他
+}
+```