观察者

src/main/java/top/fjy8018/designpattern/pattern/behavior/observer/Course.java

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+package top.fjy8018.designpattern.pattern.behavior.observer;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.extern.slf4j.Slf4j;
+
+import java.util.EventListener;
+import java.util.Observable;
+import java.util.Vector;
+
+/**
+ * 课程
+ * 被观察者类
+ * <p>
+ * {@link Observable} 使用 {@link Vector} 保证线程安全
+ * <p>
+ * JDK源码
+ * {@link java.awt.Event} 事件监听器
+ * {@link javax.servlet.ServletRequestListener} HTTP请求事件监听器
+ * 继承 {@link EventListener}，有大量实现，例如{@link org.springframework.beans.factory.parsing.ReaderEventListener}
+ *
+ * @author F嘉阳
+ * @date 2020/3/5 15:23
+ */
+@Slf4j
+@Getter
+@AllArgsConstructor
+public class Course extends Observable {
+
+    private String courseName;
+
+    /**
+     * 产生问题
+     *
+     * @param course
+     * @param question
+     */
+    public void produceQuestion(Course course, Question question) {
+        log.info("{}在{}提交了一个问题", question.getUsername(), course.getCourseName());
+        // 状态变化
+        setChanged();
+        // 通知观察者
+        notifyObservers(question);
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/observer/Question.java

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+package top.fjy8018.designpattern.pattern.behavior.observer;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+
+/**
+ * 课程问题
+ *
+ * @author F嘉阳
+ * @date 2020/3/5 15:23
+ */
+@Getter
+@AllArgsConstructor
+public class Question {
+
+    private String username;
+
+    private String content;
+
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/observer/Teacher.java

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+package top.fjy8018.designpattern.pattern.behavior.observer;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.extern.slf4j.Slf4j;
+
+import java.util.Observable;
+import java.util.Observer;
+
+/**
+ * 老师实体
+ * <p>
+ * 老师观察课程是否产生了新的问题
+ *
+ * @author F嘉阳
+ * @date 2020/3/5 15:24
+ */
+@Slf4j
+@Getter
+@AllArgsConstructor
+public class Teacher implements Observer {
+
+    private String teacherName;
+
+    /**
+     * This method is called whenever the observed object is changed. An
+     * application calls an <tt>Observable</tt> object's
+     * <code>notifyObservers</code> method to have all the object's
+     * observers notified of the change.
+     *
+     * @param o   the observable object.
+     * @param arg an argument passed to the <code>notifyObservers</code>
+     */
+    @Override
+    public void update(Observable o, Object arg) {
+        Course course = (Course) o;
+        Question question = (Question) arg;
+        log.info("{}老师的{}课程接收到一个{}提交的问题，内容为：{}",
+                teacherName, course.getCourseName(), question.getUsername(), question.getContent());
+    }
+}

src/test/java/top/fjy8018/designpattern/pattern/behavior/observer/TeacherTest.java

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+package top.fjy8018.designpattern.pattern.behavior.observer;
+
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author F嘉阳
+ * @date 2020/3/5 15:36
+ */
+@Slf4j
+class TeacherTest {
+
+    @Test
+    void update() {
+        Course course = new Course("Java设计模式");
+        Teacher teacher = new Teacher("fjy8018");
+
+        course.addObserver(teacher);
+
+        // 业务逻辑
+        Question question = new Question("fjy", "问题内容XXX");
+
+        course.produceQuestion(course, question);
+    }
+}