设计模式十二（访问者模式，mvc模式，业务代表模式）

访问者模式

 

 

 

 

public interface ComputerPart {
   public void accept(ComputerPartVisitor computerPartVisitor);
}

public class Monitor  implements ComputerPart {
 
   @Override
   public void accept(ComputerPartVisitor computerPartVisitor) {
      computerPartVisitor.visit(this);
   }
}

public class Mouse  implements ComputerPart {
 
   @Override
   public void accept(ComputerPartVisitor computerPartVisitor) {
      computerPartVisitor.visit(this);
   }
}

public class Computer implements ComputerPart {
   
   ComputerPart[] parts;
 
   public Computer(){
      parts = new ComputerPart[] {new Mouse(), new Keyboard(), new Monitor()};      
   } 
 
 
   @Override
   public void accept(ComputerPartVisitor computerPartVisitor) {
      for (int i = 0; i < parts.length; i++) {
         parts[i].accept(computerPartVisitor);
      }
      computerPartVisitor.visit(this);
   }
}

public interface ComputerPartVisitor {
   public void visit(Computer computer);
   public void visit(Mouse mouse);
   public void visit(Keyboard keyboard);
   public void visit(Monitor monitor);
}

public class ComputerPartDisplayVisitor implements ComputerPartVisitor {
 
   @Override
   public void visit(Computer computer) {
      System.out.println("Displaying Computer.");
   }
 
   @Override
   public void visit(Mouse mouse) {
      System.out.println("Displaying Mouse.");
   }
 
   @Override
   public void visit(Keyboard keyboard) {
      System.out.println("Displaying Keyboard.");
   }
 
   @Override
   public void visit(Monitor monitor) {
      System.out.println("Displaying Monitor.");
   }
}

public class VisitorPatternDemo {
   public static void main(String[] args) {
 
      ComputerPart computer = new Computer();
      computer.accept(new ComputerPartDisplayVisitor());
   }
}

Displaying Mouse.
Displaying Keyboard.
Displaying Monitor.
Displaying Computer.

总结：computer中注入父类数组，并在构造方法中实例化该数组。然后computer讲访问者作为参数执行主要方法。访问者的父类接口中会有每个compuerpart类子类。每个执行子类中属性会调用自身。利用的是重载

mvc模式

 

 

 

 

public class Student {
   private String rollNo;
   private String name;
   public String getRollNo() {
      return rollNo;
   }
   public void setRollNo(String rollNo) {
      this.rollNo = rollNo;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
}

public class StudentView {
   public void printStudentDetails(String studentName, String studentRollNo){
      System.out.println("Student: ");
      System.out.println("Name: " + studentName);
      System.out.println("Roll No: " + studentRollNo);
   }

public class StudentController {
   private Student model;
   private StudentView view;
 
   public StudentController(Student model, StudentView view){
      this.model = model;
      this.view = view;
   }
 
   public void setStudentName(String name){
      model.setName(name);    
   }
 
   public String getStudentName(){
      return model.getName();    
   }
 
   public void setStudentRollNo(String rollNo){
      model.setRollNo(rollNo);      
   }
 
   public String getStudentRollNo(){
      return model.getRollNo();     
   }
 
   public void updateView(){           
      view.printStudentDetails(model.getName(), model.getRollNo());
   }  
}

public class MVCPatternDemo {
   public static void main(String[] args) {
 
      //从数据库获取学生记录
      Student model  = retrieveStudentFromDatabase();
 
      //创建一个视图：把学生详细信息输出到控制台
      StudentView view = new StudentView();
 
      StudentController controller = new StudentController(model, view);
 
      controller.updateView();
 
      //更新模型数据
      controller.setStudentName("John");
 
      controller.updateView();
   }
 
   private static Student retrieveStudentFromDatabase(){
      Student student = new Student();
      student.setName("Robert");
      student.setRollNo("10");
      return student;
   }
}

 

}

Student: 
Name: Robert
Roll No: 10
Student: 
Name: John
Roll No: 10

 

 

 

 总结：controller注入model，和view，并将两个作为构造方法。通过controller调用model和view。

 

业务代表模式

业务代表模式（Business Delegate Pattern）用于对表示层和业务层解耦。它基本上是用来减少通信或对表示层代码中的业务层代码的远程查询功能。在业务层中我们有以下实体。

• 客户端（Client） - 表示层代码可以是 JSP、servlet 或 UI java 代码。
• 业务代表（Business Delegate） - 一个为客户端实体提供的入口类，它提供了对业务服务方法的访问。
• 查询服务（LookUp Service） - 查找服务对象负责获取相关的业务实现，并提供业务对象对业务代表对象的访问。
• 业务服务（Business Service） - 业务服务接口。实现了该业务服务的实体类，提供了实际的业务实现逻辑。

public interface BusinessService {
   public void doProcessing();
}

public class EJBService implements BusinessService {
 
   @Override
   public void doProcessing() {
      System.out.println("Processing task by invoking EJB Service");
   }
}

public class JMSService implements BusinessService {
 
   @Override
   public void doProcessing() {
      System.out.println("Processing task by invoking JMS Service");
   }
}

public class BusinessLookUp {
   public BusinessService getBusinessService(String serviceType){
      if(serviceType.equalsIgnoreCase("EJB")){
         return new EJBService();
      }else {
         return new JMSService();
      }
   }
}

public class BusinessDelegate {
   private BusinessLookUp lookupService = new BusinessLookUp();
   private BusinessService businessService;
   private String serviceType;
 
   public void setServiceType(String serviceType){
      this.serviceType = serviceType;
   }
 
   public void doTask(){
      businessService = lookupService.getBusinessService(serviceType);
      businessService.doProcessing();     
   }
}

public class Client {
   
   BusinessDelegate businessService;
 
   public Client(BusinessDelegate businessService){
      this.businessService  = businessService;
   }
 
   public void doTask(){      
      businessService.doTask();
   }
}

public class BusinessDelegatePatternDemo {
   
   public static void main(String[] args) {
 
      BusinessDelegate businessDelegate = new BusinessDelegate();
      businessDelegate.setServiceType("EJB");
 
      Client client = new Client(businessDelegate);
      client.doTask();
 
      businessDelegate.setServiceType("JMS");
      client.doTask();
   }
}

Processing task by invoking EJB Service
Processing task by invoking JMS Service

总结：BusinessLookUp根据参数进行调用指定Service，BusinessDelegate负责代理和执行业务。Client注入BusinessDelegate并执行方法。