如何组合流中的过滤器来简化

Question

我有以下方法，它接受 CustomClass 列表并使用流执行过滤器，并根据过滤器的结果在每一步返回。

我想知道是否有一种方法可以简化代码，但将过滤器和语句组合在一起，使其更加简洁和高效。

public String transform(List<CustomObject> listOfObjects) {

       listOfObjects = listOfObjects.stream()
            .filter(object -> object.objectType().equals("BUSINESS")).toList();

       // Primary check as all object should be of business type 
       // and if nothing exist we throw an exception
       if (listOfObjects.isEmpty()) {
           throw new RuntimeException("NO BUSINESS OBJECT FOUND");

       }

       // All objects are now of business type but we want them to be active
       List<CustomObject> listOfActiveObjects = listOfObjects.stream()
                     .filter(object -> object.objectStatus().equals("ACTIVE"))
                     .toList();

       // If no active object found just return the first business object sorted url

       if (listOfActiveObjects.isEmpty()) {
           return listOfObjects.stream()
                .sorted(Comparator.comparing(CustomObject::url))
                .toList().get(0).getUrl();
       }

       // Active objects are present so now filtered with proper locale

       List<CustomObject> listOfActiveObjectsWithLocale = listOfActiveObjects.stream()
                    .filter(object -> object.locale().equals("en-US"))
                    .toList();

       // If no locale was found just return the first sorted business active url

       if (listOfActiveObjectsWithLocale.isEmpty()) {
           return listOfActiveObjects.stream()
                 .sorted(Comparator.comparing(CustomObject::url))
                 .toList().get(0).getUrl();
       }

       // All filters applied, so within these objects return the sorted business/active/locale url
       return listOfActiveObjectsWithLocale.stream()
              .sorted(Comparator.comparing(CustomObject::url))
              .toList().get(0).getUrl();
   }

Answer 1

为了使其不那么复杂，您可以将过滤器与可选类一起使用。这将处理过滤过程中未找到对象的情况。

使用Java Streams内置的过滤器功能可以顺利地处理流，过滤后可以使用map函数并调用findFirst()作为故障转移机制，您可以使用orElseGet()函数

请参阅以下有关 Oracle Stream API 的官方 Oracle 指南。

https://www.oracle.com/technical-resources/articles/java/ma14-java-se-8-streams.html

https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html