服务器定位模式——配合注解实现

秒速五厘米 2022-06-13 10:25 128阅读 0赞

# 服务器定位模式——配合注解实现 #

本文主要介绍如何使用注解实现服务器定位模式。

本文主要参考：http://www.runoob.com/design-pattern/service-locator-pattern.html

服务器定位模式的使用场景：当有多个服务实现类需要根据需要进行分别调用时使用。

![Center][]

我们在使用CalServiceImpl2和CalServiceImpl1时，正常情况下会使用这样的方式。

CalService calService = new CalServiceImpl1();

CalService calService = new CalServiceImpl2();

现在要说的是使用服务器定位模式来实现调用。

下面是使用服务器定位模式的类图：

![Center 1][]

具体实现：

package com.xueyou.demo.annotation;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Provider {
        String value() default "";
    }

package com.xueyou.demo.locator;
    
    import com.xueyou.demo.service.CalService;
    import com.xueyou.demo.serviceImpl.CalServiceImpl1;
    import com.xueyou.demo.serviceImpl.CalServiceImpl2;
    
    public class CalServiceLocator {
        private static CalServiceLocator calServiceLocator;
    
        private CalServiceLocator() {
        }
    
        public static CalServiceLocator getInstance() {
            if (calServiceLocator != null) {
                return calServiceLocator;
            }
            return new CalServiceLocator();
        }
    
        public CalService getService(String serviceName) {
            CalService calService;
            if (serviceName.equals("serviceImpl1")) {
                calService = new CalServiceImpl1();
            } else if (serviceName.equals("serviceImpl2")) {
                calService = new CalServiceImpl2();
            } else {
                calService = null;
            }
            return calService;
        }
    }

package com.xueyou.demo.locator;
    
    import com.xueyou.demo.service.CalService;
    import com.xueyou.demo.serviceImpl.CalServiceImpl1;
    import com.xueyou.demo.serviceImpl.CalServiceImpl2;
    import com.xueyou.demo.serviceImpl.DefaultCalServiceImpl;
    import sun.security.jca.GetInstance;
    
    import java.util.HashMap;
    import java.util.Map;
    
    public class CalServiceLocator2 {
        private static CalServiceLocator2 calServiceLocator2;
        private static Map<String, CalService> map = new HashMap<>();
    
        private CalServiceLocator2() {
        }
    
        public static CalServiceLocator2 getInstance() {
            if (calServiceLocator2 != null) {
                return calServiceLocator2;
            }
            calServiceLocator2 = new CalServiceLocator2();
            return calServiceLocator2;
        }
    
        public void register(String code, CalService calService) {
            if (!map.containsKey(code)) {
                map.put(code, calService);
            }
        }
    
        public CalService getService(String code) {
            if (map.containsKey(code)) {
                return map.get(code);
            }
            return null;
        }
    
        public void showCache() {
            System.out.println("cache 情况 --begin");
            for (String s : map.keySet()) {
                System.out.println(s + ":" + map.get(s));
            }
            System.out.println("cache 情况 --end");
        }
    
        public void init(){
            new DefaultCalServiceImpl();
            new CalServiceImpl1();
            new CalServiceImpl2();
            System.out.println("service init ......");
        }
    }

package com.xueyou.demo.service;
    
    public interface CalService {
        public void say();
    }

package com.xueyou.demo.serviceImpl;
    
    import com.xueyou.demo.annotation.Provider;
    import com.xueyou.demo.locator.CalServiceLocator2;
    import com.xueyou.demo.service.CalService;
    
    @Provider("default")
    public class DefaultCalServiceImpl implements CalService {
        public DefaultCalServiceImpl() {
            Provider provider = this.getClass().getAnnotation(Provider.class);
            String code = provider.value();
            CalServiceLocator2.getInstance().register(code, this);
        }
    
        @Override
        public void say() {
            System.out.println(this);
            System.out.println("this is " + this.getClass().getName());
        }
    }

package com.xueyou.demo.serviceImpl;
    
    import com.xueyou.demo.annotation.Provider;
    
    @Provider(value = "service1")
    public class CalServiceImpl1 extends DefaultCalServiceImpl {
    
        @Override
        public void say() {
            System.out.println(this);
            System.out.println("this is " + this.getClass().getName());
        }
    }

package com.xueyou.demo.serviceImpl;
    
    import com.xueyou.demo.annotation.Provider;
    
    @Provider("service2")
    public class CalServiceImpl2 extends DefaultCalServiceImpl{
        @Override
        public void say() {
            System.out.println(this);
            System.out.println("this is " + this.getClass().getName());
        }
    }

package com.xueyou.demo;
    
    import com.xueyou.demo.annotation.Provider;
    import com.xueyou.demo.locator.CalServiceLocator;
    import com.xueyou.demo.locator.CalServiceLocator2;
    import com.xueyou.demo.service.CalService;
    import com.xueyou.demo.serviceImpl.CalServiceImpl1;
    import com.xueyou.demo.serviceImpl.CalServiceImpl2;
    import com.xueyou.demo.serviceImpl.DefaultCalServiceImpl;
    
    import java.lang.reflect.Field;
    
    /**
     * Hello world!
     */
    public class App {
        public static void main(String[] args) {
            CalServiceLocator2 serviceLocator2 = CalServiceLocator2.getInstance();
            serviceLocator2.showCache();
            serviceLocator2.init();
            serviceLocator2.showCache();
            CalService calService = serviceLocator2.getService("service1");
            calService.say();
            CalService calService1 = serviceLocator2.getService("service2");
            calService1.say();
        }
    }

运行结果：

![Center 2][]

[Center]: /images/20220613/645bbe7bb39b440197b3e8ee64afc442.png
[Center 1]: /images/20220613/58b7cbca23034b5198b2d1f2685a342b.png
[Center 2]: /images/20220613/0e03cccb495c49abb67c40b5b2b6972d.png