设计模式学习—服务定位模式(Service Locator Design Pattern)

向右看齐 2022-06-08 00:13 336阅读 0赞

# 一、我的理解 #

服务定位模式主要针对JNDI(Java Naming and Directory Interface， Java命名和目录接口)。利用缓存技术使得用户在访问统一服务时，可以直接从缓存中取出对象，不用重新创建。

# 二、实现方式 #

利用缓存，当用户访问某一服务时，先从缓存中检查是否有该服务对象，如果没有再重新创建该对象。

# 三、实例 #

![Center][]

###### Java实例 ######

Service接口：向外暴露的服务接口

package com.study.dp.servicelocator;
    
    public interface Service {
    
        public String getName();
        public void execute();
        
    }

Service1类：实际实现的服务一

package com.study.dp.servicelocator;
    
    public class Service1 implements Service {
    
        @Override
        public String getName() {
            return "Service1";
        }
    
        @Override
        public void execute() {
            System.out.println("Executing Service1");
        }
    
    }

Service2类：实际实现的服务二

package com.study.dp.servicelocator;
    
    public class Service2 implements Service {
    
        @Override
        public String getName() {
            return "Service2";
        }
    
        @Override
        public void execute() {
            System.out.println("Executing Service2");
        }
    
    }

InitialContext类：初始化上下文，即服务的提供方

package com.study.dp.servicelocator;
    
    public class InitialContext {
    
        public Object lookup(String jndiName) {
            if(jndiName.equalsIgnoreCase("SERVICE1")) {
                System.out.println("Looking up and creating a new Service1 object");
                return new Service1();
            }else if(jndiName.equalsIgnoreCase("SERVICE2")) {
                System.out.println("Looking up and creating a new Service2 object");
                return new Service2();
            }
            return null;
        }
        
    }

Cache类：缓存类

package com.study.dp.servicelocator;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class Cache {
    
        private List<Service> services;
        
        public Cache() {
            services = new ArrayList<>();
        }
        
        public Service getService(String serviceName) {
            for(Service service:services) {
                if(service.getName().equalsIgnoreCase(serviceName)) {
                    System.out.println("Returning cached "+serviceName+" object");
                    return service;
                }
            }
            return null;
        }
        
        public void addService(Service newService) {
            boolean exists = false;
            for(Service service:services) {
                if(service.getName().equalsIgnoreCase(newService.getName())) {
                    exists = true;
                    break;
                }
            }
            if(!exists) {
                services.add(newService);
            }
        }
        
    }

ServiceLocator类：服务定位类，该类负责获取对应服务对象

package com.study.dp.servicelocator;
    
    public class ServiceLocator {
    
        private static Cache cache;
        
        static {
            cache  = new Cache();
        }
        
        public static Service getService(String jndiName) {
            Service service = cache.getService(jndiName);
            if(service!=null) {
                return service;
            }
            
            InitialContext context = new InitialContext();
            service = (Service)context.lookup(jndiName);
            cache.addService(service);
            return service;
        }
        
    }

Demo类：测试类

package com.study.dp.servicelocator;
    
    public class Demo {
    
        public static void main(String[] args) {
            Service service = ServiceLocator.getService("Service1");
            service.execute();
            service = ServiceLocator.getService("Service2");
            service.execute();
            service = ServiceLocator.getService("Service1");
            service.execute();
            service = ServiceLocator.getService("Service2");
            service.execute();
        }
        
    }

# 四、应用场景 #

[Center]: /images/20220608/875d20c2d5d040f9836569c56d59fcbd.png