事件監聽器模式與Spring事件機制
1.事件監聽器模式簡單使用
比如監聽門開關改變事件以及name改變事件。
1.事件相關類
抽象門事件
package cn.qlq.event.base; import java.util.EventObject; public abstract class DoorEvent extends EventObject { private static final long serialVersionUID = 7099057708183571937L; /** * 事件發生時間 */ private final long timestamp;public DoorEvent(Object source) { super(source); this.timestamp = System.currentTimeMillis(); } public final long getTimestamp() { return this.timestamp; } }
門name改變事件
package cn.qlq.event.base; /** * 門改變事件 * * @author Administrator * */ public class DoorNameChangeEvent extendsDoorEvent { private static final long serialVersionUID = 2106840053610489753L; private String originName; private String newName; public DoorNameChangeEvent(Object source, String originName, String newName) { super(source); this.originName = originName; this.newName = newName; }public String getOriginName() { return originName; } public void setOriginName(String originName) { this.originName = originName; } public String getNewName() { return newName; } public void setNewName(String newName) { this.newName = newName; } }
門狀態改變事件
package cn.qlq.event.base; /** * 門改變事件 * * @author Administrator * */ public class DoorStatusChangeEvent extends DoorEvent { private static final long serialVersionUID = 2106840053610489753L; private String originStatus; private String newStatus; public DoorStatusChangeEvent(Object source, String originStatus, String newStatus) { super(source); this.originStatus = originStatus; this.newStatus = newStatus; } public String getOriginStatus() { return originStatus; } public void setOriginStatus(String originStatus) { this.originStatus = originStatus; } public String getNewStatus() { return newStatus; } public void setNewStatus(String newStatus) { this.newStatus = newStatus; } }
2.監聽器相關類
抽象監聽器類
package cn.qlq.event.base; import java.util.EventListener; public interface DoorListener<E extends DoorEvent> extends EventListener { void onEvent(E event); }
門name改變事件監聽器
package cn.qlq.event.base; public class DoorNameChangeListener implements DoorListener<DoorNameChangeEvent> { @Override public void onEvent(DoorNameChangeEvent event) { System.out.println("=============門name改變===========" + event.getTimestamp()); System.out.println("原來name: " + event.getOriginName()); System.out.println("最新name: " + event.getNewName()); } }
門status改變事件監聽器
package cn.qlq.event.base; public class DoorStatusChangeListener implements DoorListener<DoorStatusChangeEvent> { @Override public void onEvent(DoorStatusChangeEvent event) { System.out.println("=============門status改變===========" + event.getTimestamp()); System.out.println("原來狀態: " + event.getOriginStatus()); System.out.println("最新狀態: " + event.getNewStatus()); } }
3.門類
addListener方法獲取到泛型的實際引數然後將listener快取到cache屬性中,用於釋出事件。publishEvent釋出事件根據事件對應的typeName到cache中找到listener集合,然後釋出事件。
package cn.qlq.event.base; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class Door { // 快取事件監聽器 private Map<String, List<DoorListener<? extends DoorEvent>>> cache = new HashMap<>(); public String status; public String getStatus() { return status; } public void setStatus(String status) { if (status != null && !status.equals(this.status)) { publishEvent(new DoorStatusChangeEvent(this, this.status, status)); } this.status = status; } public void addListener(DoorListener<? extends DoorEvent> listener) { // 獲取到介面。根據介面獲取到泛型 Type[] genericInterfaces = listener.getClass().getGenericInterfaces(); Type type = genericInterfaces[0]; if (type instanceof ParameterizedType) { ParameterizedType typeTmp = (ParameterizedType) type; // 原始型別。例如 interface cn.qlq.event.base.DoorListener Type rawType = typeTmp.getRawType(); // 獲取到實際引數型別 Type[] actualTypeArguments = typeTmp.getActualTypeArguments(); Type type2 = actualTypeArguments[0]; String actuallyTypeName = type2.getTypeName(); List<DoorListener<? extends DoorEvent>> list = cache.get(actuallyTypeName); if (list == null) { list = new ArrayList<DoorListener<? extends DoorEvent>>(); cache.put(actuallyTypeName, list); } list.add(listener); } } public <E extends DoorEvent> void publishEvent(E event) { String typeName = event.getClass().getTypeName(); List<DoorListener<? extends DoorEvent>> list = cache.get(typeName); for (DoorListener doorListener : list) { doorListener.onEvent(event); } } }
4.客戶端測試程式碼
package cn.qlq.event.base; public class Client { public static void main(String[] args) { Door door = new Door(); door.addListener(new DoorStatusChangeListener()); door.addListener(new DoorNameChangeListener()); // 釋出事件 door.publishEvent(new DoorNameChangeEvent(door, "木門", "鐵門")); door.setStatus("close"); door.setStatus("close"); door.setStatus("open"); } }
結果:
=============門name改變===========1594192130541
原來name: 木門
最新name: 鐵門
=============門status改變===========1594192130541
原來狀態: null
最新狀態: close
=============門status改變===========1594192130541
原來狀態: close
最新狀態: open
補充:Type與Class的區別
檢視JDK原始碼,發現有個Type類,而且是從1.5引入的。如下:
/** <a href="http://www.cpupk.com/decompiler">Eclipse Class Decompiler</a> plugin, Copyright (c) 2017 Chen Chao. */ package java.lang.reflect; /** * Type is the common superinterface for all types in the Java * programming language. These include raw types, parameterized types, * array types, type variables and primitive types. * * @since 1.5 */ public interface Type { /** * Returns a string describing this type, including information * about any type parameters. * * @implSpec The default implementation calls {@code toString}. * * @return a string describing this type * @since 1.8 */ default String getTypeName() { return toString(); } }
Type是Class的父介面。Type 是 Java 程式語言中所有型別的公共高階介面。它們包括原始型別、引數化型別、陣列型別、型別變數和基本型別。Type可以表示出泛型的型別,而Class不能。
如果想要獲取泛型型別的陣列,可以將Type轉化為它的子介面ParameterizedType,通過getActualTypeArguments() 獲取。參考上面的:Door類的addListener方法。
另外:java中8種基本資料型別和void也有class物件。如下Integer類的方法:
public static final Class<Integer> TYPE = (Class<Integer>) Class.getPrimitiveClass("int");
測試如下:
getGenericSuperclass() 方法獲取父類的Type;getGenericInterfaces()方法獲取所有實現介面的Type。Type可以用於獲取泛型的實際型別。ParameterizedType 型別的例項可以獲取到原始型別和實際型別。
package cn.qlq.event.base; import java.lang.reflect.Type; import java.lang.reflect.TypeVariable; import java.util.Arrays; public class Client<T> { private T prop; public static void main(String[] args) { System.out.println(int.class.isPrimitive()); System.out.println(Integer.class.isPrimitive()); System.out.println("==========="); Client<String> client = new Client<String>(); printObj(client); Integer integer = new Integer(1); printObj(integer); Integer[] integers = { 1, 3 }; printObj(integers); } private static void printObj(Object obj) { System.out.println("==========="); Class<?> class2 = obj.getClass(); System.out.println(class2); System.out.println(class2.getTypeName()); Type genericSuperclass2 = class2.getGenericSuperclass(); System.out.println(genericSuperclass2); Type[] genericInterfaces2 = class2.getGenericInterfaces(); System.out.println(Arrays.asList(genericInterfaces2)); TypeVariable<?>[] typeParameters = class2.getTypeParameters(); System.out.println(Arrays.asList(typeParameters)); } public T getProp() { return prop; } public void setProp(T prop) { this.prop = prop; } }
結果:
true
false
===========
===========
class cn.qlq.event.base.Client
cn.qlq.event.base.Client
class java.lang.Object
[]
[T]
===========
class java.lang.Integer
java.lang.Integer
class java.lang.Number
[java.lang.Comparable<java.lang.Integer>]
[]
===========
class [Ljava.lang.Integer;
java.lang.Integer[]
class java.lang.Object
[interface java.lang.Cloneable, interface java.io.Serializable]
[]
2.Spring的事件
1. 標準事件
Spring的ApplicationContext 提供了支援事件和程式碼中監聽器的功能。
我們可以建立bean用來監聽在ApplicationContext 中釋出的事件。ApplicationEvent類和在ApplicationContext介面中處理的事件,如果一個bean實現了ApplicationListener介面,當一個ApplicationEvent 被髮布以後,bean會自動被通知。
Spring 提供了以下5種標準的事件:
1. 上下文更新事件(ContextRefreshedEvent):該事件會在ApplicationContext被初始化或者更新時釋出。也可以在呼叫ConfigurableApplicationContext 介面中的refresh()方法時被觸發。
2. 上下文開始事件(ContextStartedEvent):當容器呼叫ConfigurableApplicationContext的Start()方法開始/重新開始容器時觸發該事件。
3. 上下文停止事件(ContextStoppedEvent):當容器呼叫ConfigurableApplicationContext的Stop()方法停止容器時觸發該事件。
4. 上下文關閉事件(ContextClosedEvent):當ApplicationContext被關閉時觸發該事件。容器被關閉時,其管理的所有單例Bean都被銷燬。
5. 請求處理事件(RequestHandledEvent):在Web應用中,當一個http請求(request)結束觸發該事件
比如經常在容器啟動後建立預設使用者等操作:
package cn.qlq.event; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.ApplicationListener; import org.springframework.context.event.ContextRefreshedEvent; import org.springframework.stereotype.Component; import cn.qlq.service.user.UserService; /** * 上下文更新事件(ContextRefreshedEvent):該事件會在ApplicationContext被初始化或者更新時釋出。 * 也可以在呼叫ConfigurableApplicationContext 介面中的refresh()方法時被觸發。 * * @author Administrator * */ @Component public class ContextRefreshedEventListener implements ApplicationListener<ContextRefreshedEvent> { @Autowired private UserService userService; @Override public void onApplicationEvent(ContextRefreshedEvent event) { System.out.println("ContextRefreshedEvent=========== 容器啟動完成"); System.out.println(event); // 建立預設使用者 // userService.addUser(user); } }
啟動後控制檯:
ContextRefreshedEvent=========== 容器啟動完成
org.springframework.context.event.ContextRefreshedEvent[source=org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@13b3d178, started on Wed Jul 08 16:28:45 CST 2020]
2020/07/08-16:29:00 [main] INFO cn.qlq.MySpringBootApplication Started MySpringBootApplication in 15.976 seconds (JVM running for 17.039)
2.自定義事件
1.定義事件
package cn.qlq.event; import org.springframework.context.ApplicationEvent; public class CustomApplicationEvent extends ApplicationEvent { private String msg; private static final long serialVersionUID = -9184671635725233773L; public CustomApplicationEvent(Object source, final String msg) { super(source); this.msg = msg; } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } }
2.定義監聽器
package cn.qlq.event; import org.springframework.context.ApplicationListener; import org.springframework.stereotype.Component; @Component public class CustomEventListener implements ApplicationListener<CustomApplicationEvent> { @Override public void onApplicationEvent(CustomApplicationEvent applicationEvent) { // handle event System.out.println("收到事件,訊息為:" + applicationEvent.getMsg()); System.out.println(applicationEvent); } }
3.程式碼釋出事件
@Controller public class LoginController { @Autowired private ApplicationContext applicationContext;/** * 跳轉到登陸介面 * * @return */ @RequestMapping("login") public String login() { applicationContext.publishEvent(new CustomApplicationEvent(this, "有人訪問登陸")); return "login"; } }
結果:
收到事件,訊息為:有人訪問登陸
cn.qlq.event.CustomApplicationEvent[source=cn.qlq.controller.system.LoginController@333a44f2]