使用 Java 8 重构多态性

Question

我有一个旧代码库，需要使用 Java 8 重构，所以我有一个接口，它告诉我当前站点是否支持该平台。

public interface PlatformSupportHandler {   
  public abstract boolean isPaltformSupported(String platform);
}

我有多个实现它的类，每个类支持不同的平台。

一些实现类是：

@Component("bsafePlatformSupportHandler")
public class BsafePlatoformSupportHandler implements PlatformSupportHandler {

  String[] supportedPlatform = {"iPad", "Android", "iPhone"};
  Set<String> supportedPlatformSet = new HashSet<>(Arrays.asList(supportedPlatform)); 

  @Override
  public boolean isPaltformSupported(String platform) {

    return supportedPlatformSet.contains(platform);
  }

}

另一种实现：

@Component("discountPlatformSupportHandler")
public class DiscountPlatoformSupportHandler implements PlatformSupportHandler{

  String[] supportedPlatform = {"Android", "iPhone"};
  Set<String> supportedPlatformSet = new HashSet<>(Arrays.asList(supportedPlatform)); 

  @Override
  public boolean isPaltformSupported(String platform) {

  return supportedPlatformSet.contains(platform);
  }
}

在我的过滤器运行时，我得到了我想要的所需 bean：

platformSupportHandler = (PlatformSupportHandler) ApplicationContextUtil
  .getBean(subProductType + Constants.PLATFORM_SUPPORT_HANDLER_APPEND);

并致电isPlatformSupported 了解我当前的站点是否支持以下平台。

我是 Java 8 的新手，有什么方法可以在不创建多个类的情况下重构此代码？由于接口只包含一个方法，我能不能用 lambda 来重构它？

Answer 1

如果你想坚持当前的设计，你可以这样做：

public class MyGeneralPurposeSupportHandler implements PlatformSupportHandler {
   private final Set<String> supportedPlatforms;
   public MyGeneralPurposeSupportHandler(Set<String> supportedPlatforms) {
      this.supportedPlatforms = supportedPlatforms;
   } 

   public boolean isPlatformSupported(String platform) {
     return supportedPlatforms.contains(platform);
   }
}

// now in configuration:

@Configuration
class MySpringConfig {

    @Bean
    @Qualifier("discountPlatformSupportHandler") 
    public PlatformSupportHandler discountPlatformSupportHandler() {
       return new MyGeneralPurposeSupportHandler(new HashSefOf({"Android", "iPhone"})); // yeah its not a java syntax, but you get the idea
    }

    @Bean
    @Qualifier("bsafePlatformSupportHandler") 
    public PlatformSupportHandler bsafePlatformSupportHandler() {
       return new MyGeneralPurposeSupportHandler(new HashSefOf({"Android", "iPhone", "iPad"}));
    }   

}

此方法的优点是不为每种类型（折扣、bsafe 等）创建类，因此这回答了问题。

更进一步，如果没有请求类型会发生什么，目前它将失败，因为 bean 不存在于应用程序上下文中 - 这不是一个真正好的方法。

因此，您可以创建一个类型映射到一组受支持的平台，在配置中维护映射或让 spring 发挥它的魔力。 你最终会得到这样的结果：

public class SupportHandler {

   private final Map<String, Set<String>> platformTypeToSuportedPlatforms;

   public SupportHandler(Map<String, Set<String>> map) {
       this.platformTypeToSupportedPlatforms = map; 
   }

   public boolean isPaltformSupported(String type) {
        Set<String> supportedPlatforms = platformTypeToSupportedPlatforms.get(type);
        if(supportedPlatforms == null) {
          return false; // or maybe throw an exception, the point is that you don't deal with spring here which is good since spring shouldn't interfere with your business code
        }
        return supportedPlatforms.contains(type);

   }
}

@Configuration 
public class MyConfiguration {

    // Configuration conf is supposed to be your own way to read configurations in the project - so you'll have to implement it somehow
    @Bean
    public SupportHandler supportHandler(Configuration conf) {
      return new SupportHandler(conf.getRequiredMap());
    }
}

现在，如果您采用这种方法，添加新的受支持类型就完全没有代码了，您只需添加一个配置，这是迄今为止我能提供的最佳方法。

不过，这两种方法都缺少 java 8 的特性；)

Answer 2

您可以在可以创建 bean 的配置类中使用以下内容：

@Configuration 
public class AppConfiguration {

    @Bean(name = "discountPlatformSupportHandler")
    public PlatformSupportHandler discountPlatformSupportHandler() {
        String[] supportedPlatforms = {"Android", "iPhone"};
        return getPlatformSupportHandler(supportedPlatforms);
    }

    @Bean(name = "bsafePlatformSupportHandler")
    public PlatformSupportHandler bsafePlatformSupportHandler() {
        String[] supportedPlatforms = {"iPad", "Android", "iPhone"};
        return getPlatformSupportHandler(supportedPlatforms);
    }

    private PlatformSupportHandler getPlatformSupportHandler(String[] supportedPlatforms) {
        return platform -> Arrays.asList(supportedPlatforms).contains(platform);
    }
}

另外，当你想使用 bean 时，也很简单：

@Component
class PlatformSupport {

    // map of bean name vs bean, automatically created by Spring for you
    private final Map<String, PlatformSupportHandler> platformSupportHandlers;

    @Autowired // Constructor injection
    public PlatformSupport(Map<String, PlatformSupportHandler> platformSupportHandlers) {
        this.platformSupportHandlers = platformSupportHandlers;
    }

    public void method1(String subProductType) {
        PlatformSupportHandler platformSupportHandler = platformSupportHandlers.get(subProductType + Constants.PLATFORM_SUPPORT_HANDLER_APPEND);
    }
}

---

Answer 3

正如Mark Bramnik's 回答中所写，您可以将其移至配置。

假设它会以这种方式在 yaml 中：

platforms:
    bsafePlatformSupportHandler: ["iPad", "Android", "iPhone"]
    discountPlatformSupportHandler: ["Android", "iPhone"]

然后你可以创建配置类来阅读这个：

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties
public class Config {

    private Map<String, List<String>> platforms = new HashMap<String, List<String>>();

    // getters and setters

您可以创建带有检查代码的处理程序。 或者将其放在您的过滤器中，如下所示：

@Autowired
private Config config;

...

public boolean isPlatformSupported(String subProductType, String platform) {
    String key = subProductType + Constants.PLATFORM_SUPPORT_HANDLER_APPEND;
    return config.getPlatforms()
        .getOrDefault(key, Collections.emptyList())
        .contains(platform);
}