使用Java 8重构多态性

Question

我有一个老的代码库需要使用Java 8重构，因此我有一个接口，用于判断当前网站是否支持该平台。

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

我有多个实现它的类，每个类都支持不同的平台。

其中一些实现类包括：

@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);
  }
}

在我的过滤器中，在运行时获取我所需的bean：

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

然后调用isPlatformSupported来获取当前网站是否支持以下平台。

我对Java 8还很陌生，所以有没有办法在不创建多个类的情况下重构这段代码？由于接口只包含一个方法，我能否使用lambda表达式进行重构？

- Shubham Chopra

---

撇开Spring不谈，你所做的只是对一个集合进行包含检查。将该集合作为构造函数参数注入即可。 - Andy Turner

Answer 1

如果您想保留当前的设计，可以采用以下方法：

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"}));
    }   

}

这种方法的优点在于不会为每一种类型（如 discount、bsafe 等）创建一个类，因此它能够回答这个问题。

更进一步，如果没有请求的类型，那会发生什么呢？目前会因为应用程序上下文中不存在该 bean 而失败，这并不是一个很好的方法。

所以你可以创建一个类型到支持平台集合的映射，在配置中维护这个映射或其他方式，并让 Spring 发挥其魔力。最终你将得到像这样的东西：

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());
    }
}

如�您采用这�方法，添加新的支�类�将�得毫无代�难度，您�需添加�置��，这是目�我所能�供的最佳方法。

�过，这两�方法都缺�Java 8的特性😉

- Mark Bramnik

Answer 2

您可以在您的配置类中使用以下内容，以便您可以创建bean：

@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);
    }
}

此外，当您想要使用该bean时，非常容易：

@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);
    }
}

---

- rohanagarwal

Answer 3

正如Mark Bramnik的回答所述，您可以将此移动到配置文件中。

假设它会以以下方式出现在yaml文件中：

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

然后，您可以创建配置类来读取此内容：

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties
public class Config {

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

    // getters and setters

您可以使用检查代码创建处理程序。 或者像下面这样将其放置在您的过滤器中：

@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);
}

- lczapski