add custom springboot event listener readme

Author: ipipman

springboot-source-code-analysis/(8)自定义监听器实战.md

@@ -1,23 +1,100 @@
 ### 自定义监听器实战
 
+#### 实现方式一
 
+- 实现ApplicationListener接口，ApplicationListener<ApplicationStartedEvent>声明感兴趣的事件
 
-![image-20210921163734877](/Users/huangyan110110114/Library/Application Support/typora-user-images/image-20210921163734877.png)
+```java
+@Order(1)
+public class FirstListener implements ApplicationListener<ApplicationStartedEvent> {
 
+    private final static Logger logger = LoggerFactory.getLogger(FirstListener.class);
 
+    @Override
+    public void onApplicationEvent(ApplicationStartedEvent event) {
+        logger.info("设置框架事件监听器【ApplicationListener】成功 : run firstListener");
 
+    }
+}
 
+```
 
+- 在spring.factories 配置文件中配置FirstListener事件监听器，key值为org.springframework.context.ApplicationListener
 
+```java
+# 通过系统事件监听器，设置自定义事件监听器
+org.springframework.context.ApplicationListener=\
+  com.example.springboot.source.code.analysis.listener.FirstListener
+```
 
 
 
-![image-20210921163836397](/Users/huangyan110110114/Library/Application Support/typora-user-images/image-20210921163836397.png)
+#### 实现方式三
 
+- 实现ApplicationListener接口，声明感兴趣的事件ApplicationListener<ApplicationStartedEvent>
 
+```java
+@Order(3)
+public class ThirdListener implements ApplicationListener<ApplicationStartedEvent> {
 
+    private final static Logger logger = LoggerFactory.getLogger(ThirdListener.class);
 
+    @Override
+    public void onApplicationEvent(ApplicationStartedEvent event) {
+        logger.info("设置框架事件监听器【ApplicationListener】成功 : run thirdListener");
+    }
+}
+```
+
+- 在application.properties 内配置事件监听器，key值为context.listener.classes
+
+```java
+# 通过系统事件监听器，监听事件
+context.listener.classes=\
+  com.example.springboot.source.code.analysis.listener.ThirdListener,\
+```
+
+> application.properties 内配置的 conext.listener.classes 事件监听器执行优先级最高
+>
+> ```java
+> // context.listener.classes 是通过 DelegatingApplicationListener 委派给 ApplicationListener
+> public class DelegatingApplicationListener implements ApplicationListener<ApplicationEvent>, Ordered {
+>     private static final String PROPERTY_NAME = "context.listener.classes";
+>     // 在委派过程中，DelegatingApplicationListener 会将 order 优先级设置为最高
+>     private int order = 0;
+>     private SimpleApplicationEventMulticaster multicaster;
+> 
+> ```
+
+
+
+#### 实现方式四
+
+- 实现SmartApplicationListener接口
+
+```java
+@Order(4)
+public class FourthListener implements SmartApplicationListener {
+
+    private final static Logger logger = LoggerFactory.getLogger(FourthListener.class);
+
+    // 通过重写 supportEventType()方法 判断该监听器对哪些事件感兴趣
+    @Override
+    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
+        return ApplicationStartedEvent.class.isAssignableFrom(eventType)
+                || ApplicationPreparedEvent.class.isAssignableFrom(eventType);
+    }
+
+    // 编写事件触发逻辑
+    @Override
+    public void onApplicationEvent(ApplicationEvent event) {
+        logger.info("设置框架事件监听器【SmartApplicationListener】成功 : run fourthListener");
+    }
+}
+
+```
+
+- 可以通过spring.factories 或 application.properties 或 new SpringApplication().addListeners() 三种方式注入该事件
 
 
 
-![image-20210921163902692](/Users/huangyan110110114/Library/Application Support/typora-user-images/image-20210921163902692.png)