设计模式十二（访问者模式，mvc模式，业务代表模式）

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.

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

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