java - 如何使用Stream API从对象中检索嵌套列表？

Question

你知道如何检索所有SimpleProperty吗？来自 TopComplexity目的？
我需要改变那个 for 循环 进入 流 “亲切”的一段代码。

@Data
public class TopComplexity {
   List<SuperComplexProperty> superComplexProperties;
}
@Data
public class SuperComplexProperty {
   List<SimpleProperty> simpleProperties;
   ComplexProperty complexProperty;
}

@Data
public class ComplexProperty {
   List<SimpleProperty> simpleProperties;
}

public class MainClass {
   public static void main(String[] args) {

       TopComplexity top = null;
       List<SimpleProperty> result = new ArrayList<>();
      
       for(SuperComplexProperty prop : top.getSuperComplexProperties) {
          result.addAll(prop.getSimpleProperties());
      
          if(Objects.nonNull(prop.getComplexProperty()) {
              result.addAll(prop.getComplexProperty().getSimpleProperties());
         }
      }
   }
}

真的很感谢任何帮助

Answer 1

你可以混淆 flatMap带有涉及 Stream 的连接和三元运算符比如:

List<SimpleProperty> result = top.getSuperComplexProperties().stream()
        .flatMap(scp -> Stream.concat(
                scp.getSimpleProperties().stream(),
                scp.getComplexProperty() == null ?
                        Stream.empty() :
                        scp.getComplexProperty().getSimpleProperties().stream()))
        .collect(Collectors.toList());