[Design Pattern] Service Locator Pattern 简单案例

时间 2019-11-24

标签 design pattern service locator 简单案例繁體版

原文原文链接

Service Locator Pattern，即服务定位模式，用于定位不一样的服务。考虑到 InitialContext::lookup 的成本比较高，提供了 Cache 类缓存以定位到的服务。缓存

代码实现ide

Service 接口spa

public interface Service {

    public String getName();
    
    public void execute();
}

Service1, Service2 实现 Service 接口，提供具体服务code

public class Service1 implements Service {

    private String name = "service1";
    
    @Override
    public String getName() {
        return name;
    }

    @Override
    public void execute() {
        System.out.println(name + "executing");
    }
}

public class Service2 implements Service {

    private String name = "service2";

    @Override
    public String getName() {
        return name;
    }

    @Override
    public void execute() {
        System.out.println(name + " executing");
    }
}

InitialContext 用于查找并初始化服务htm

public class InitialContext {

    public static Service lookup(String jndiName){
        
        System.out.println(" initializing " + jndiName);
        
        if (jndiName.equals("service1")){
            return new Service1();
        }
        else if(jndiName.equals("service2")){
            return new Service2();
        }
        else{
            System.out.println("cannot find " + jndiName);
        }
        
        return null;
    }
}

ServiceLocator 是在 InitialConext 以前的一个层，把已找到的服务缓存起来，避免重复建立服务。blog

public class ServiceLocator {

    private static Cache cache = new Cache();
    
    public static Service getService(String serviceName){
        Service service = cache.getService(serviceName);
        
        if (service == null){
            service = InitialContext.lookup(serviceName);
            cache.addService(service);
        }    
        return service;
    }    
}

演示服务定位模式。接口

public class ServiceLocatorPatternDemo {

    public static void main() {
        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();
    }
}

注：get

为了简化模式关系演示，本案例没有处理找不到服务的状况，能够在 InitialContext::lookup 和 ServiceLocator::getService 方法声明爆出异常，交由客户端代码处理服务没法找到的状况。it

参考资料class

Design Pattern - Service Locator Pattern, TutorialsPoint