小傅哥 | 重学 Java 设计模式：实战访问者模式「模拟家长与校长，对学生和老师的不同视角信息的访问场景」

itstack-demo-design-22-00/pom.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>itstack-demo-design</artifactId>
+        <groupId>org.itstack</groupId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>itstack-demo-design-22-00</artifactId>
+
+
+</project>
\ No newline at end of file

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/DataView.java

+package org.itstack.demo.design;
+
+import org.itstack.demo.design.user.User;
+import org.itstack.demo.design.user.impl.Student;
+import org.itstack.demo.design.user.impl.Teacher;
+import org.itstack.demo.design.visitor.Visitor;
+
+import java.util.ArrayList;
+import java.util.List;
+
+// 数据看版
+public class DataView {
+
+    List<User> userList = new ArrayList<User>();
+
+    public DataView() {
+        userList.add(new Student("谢飞机", "重点班", "一年一班"));
+        userList.add(new Student("windy", "重点班", "一年一班"));
+        userList.add(new Student("大毛", "普通班", "二年三班"));
+        userList.add(new Student("Shing", "普通班", "三年四班"));
+        userList.add(new Teacher("BK", "特级教师", "一年一班"));
+        userList.add(new Teacher("娜娜Goddess", "特级教师", "一年一班"));
+        userList.add(new Teacher("dangdang", "普通教师", "二年三班"));
+        userList.add(new Teacher("泽东", "实习教师", "三年四班"));
+    }
+
+    // 展示
+    public void show(Visitor visitor) {
+        for (User user : userList) {
+            user.accept(visitor);
+        }
+    }
+
+}

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/user/User.java

+package org.itstack.demo.design.user;
+
+import org.itstack.demo.design.visitor.Visitor;
+
+// 基础用户信息
+public abstract class User {
+
+    public String name;      // 姓名
+    public String identity;  // 身份；重点班、普通班 | 特级教师、普通教师、实习教师
+    public String clazz;     // 班级
+
+    public User(String name, String identity, String clazz) {
+        this.name = name;
+        this.identity = identity;
+        this.clazz = clazz;
+    }
+
+    // 核心访问方法
+    public abstract void accept(Visitor visitor);
+
+}

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/user/impl/Student.java

+package org.itstack.demo.design.user.impl;
+
+import org.itstack.demo.design.user.User;
+import org.itstack.demo.design.visitor.Visitor;
+
+// 学生
+public class Student extends User {
+
+    public Student(String name, String identity, String clazz) {
+        super(name, identity, clazz);
+    }
+
+    public void accept(Visitor visitor) {
+        visitor.visit(this);
+    }
+
+    public int ranking() {
+        return (int) (Math.random() * 100);
+    }
+
+}

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/user/impl/Teacher.java

+package org.itstack.demo.design.user.impl;
+
+import org.itstack.demo.design.user.User;
+import org.itstack.demo.design.visitor.Visitor;
+
+import java.math.BigDecimal;
+
+// 老师
+public class Teacher extends User {
+
+    public Teacher(String name, String identity, String clazz) {
+        super(name, identity, clazz);
+    }
+
+    public void accept(Visitor visitor) {
+        visitor.visit(this);
+    }
+
+    // 升本率
+    public double entranceRatio() {
+        return BigDecimal.valueOf(Math.random() * 100).setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
+    }
+
+}

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/visitor/Visitor.java

+package org.itstack.demo.design.visitor;
+
+import org.itstack.demo.design.user.impl.Student;
+import org.itstack.demo.design.user.impl.Teacher;
+
+public interface Visitor {
+
+    // 访问学生信息
+    void visit(Student student);
+
+    // 访问老师信息
+    void visit(Teacher teacher);
+
+}

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/visitor/impl/Parent.java

+package org.itstack.demo.design.visitor.impl;
+
+import org.itstack.demo.design.user.impl.Student;
+import org.itstack.demo.design.user.impl.Teacher;
+import org.itstack.demo.design.visitor.Visitor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+// 家长
+public class Parent implements Visitor {
+
+    private Logger logger = LoggerFactory.getLogger(Parent.class);
+
+    public void visit(Student student) {
+        logger.info("学生信息 姓名：{} 班级：{} 排名：{}", student.name, student.clazz, student.ranking());
+    }
+
+    public void visit(Teacher teacher) {
+        logger.info("老师信息 姓名：{} 班级：{} 级别：{}", teacher.name, teacher.clazz, teacher.identity);
+    }
+
+}

itstack-demo-design-22-00/src/main/java/org/itstack/demo/design/visitor/impl/Principal.java

+package org.itstack.demo.design.visitor.impl;
+
+import org.itstack.demo.design.user.impl.Student;
+import org.itstack.demo.design.user.impl.Teacher;
+import org.itstack.demo.design.visitor.Visitor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+// 校长
+public class Principal implements Visitor {
+
+    private Logger logger = LoggerFactory.getLogger(Principal.class);
+
+    public void visit(Student student) {
+        logger.info("学生信息 姓名：{} 班级：{}", student.name, student.clazz);
+    }
+
+    public void visit(Teacher teacher) {
+        logger.info("学生信息 姓名：{} 班级：{} 升学率：{}", teacher.name, teacher.clazz, teacher.entranceRatio());
+    }
+
+}

itstack-demo-design-22-00/src/test/java/org/itstack/demo/design/test/ApiTest.java

+package org.itstack.demo.design.test;
+
+import org.itstack.demo.design.DataView;
+import org.itstack.demo.design.visitor.impl.Parent;
+import org.itstack.demo.design.visitor.impl.Principal;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class ApiTest {
+
+    private Logger logger = LoggerFactory.getLogger(ApiTest.class);
+
+    @Test
+    public void test(){
+        DataView dataView = new DataView();
+
+        logger.info("\r\n家长视角访问：");
+        dataView.show(new Parent());     // 家长
+
+        logger.info("\r\n校长视角访问：");
+        dataView.show(new Principal());  // 校长
+    }
+
+}

pom.xml

@@ -58,6 +58,7 @@
         <module>itstack-demo-design-20-01</module>
         <module>itstack-demo-design-20-02</module>
         <module>itstack-demo-design-21-00</module>
+        <module>itstack-demo-design-22-00</module>
     </modules>
 
     <dependencies>