Java Streams功能转换/丰富数据

如何解决Java Streams功能转换/丰富数据

我想将DataX写入List<DataY>变换/丰富函数

class DataX {
    private String a;
    private List<String> c;
}

class DataY {
    private String a;
    private String b;
    private String cx;
}

JSON表示形式

输入

{
    "a": "abc-123","c": ["c1","c2","c3","c4","c5"]
}

在处理c的每个元素时，将根据查找表（可以是数据库，本地缓存或REST查找）检查该值，并且某些值会从1映射到许多。

c1 -> c1 
c2 -> c2 
c3 -> c31,c32,c33 
c4 -> c4 
c5 -> c51,c52

预期输出

[
    {
        "a": "abc-123","b": "xyz-1","cx": "c1"
    },{
        "a": "abc-123","b": "xyz-2","cx": "c2"
    },"b": "xyz-3","cx": "c31"
    },"b": "xyz-4","cx": "c32"
    },"b": "xyz-5","cx": "c33"
    },"b": "xyz-6","cx": "c4"
    },"b": "xyz-7","cx": "c51"
    },"b": "xyz-8","cx": "c52"
    }
]

注意：值b表示通过UUID.randomUUID（）方法生成的UUID

---

我的尝试

public class Test {
    public static void main(String[] args) {
        DataX dataX = new DataX("abc-123",Arrays.asList("c1","c5"));

        List<DataY> collect = dataX.getC().stream()
                .map(c -> new DataY(dataX.getA(),UUID.randomUUID().toString(),c))
                .map(dataY -> {       // use flatMap here?
                    if (isOneToMany(dataY.getCx()))
                        return operationOneToMany(dataY.getCx());
                    else
                        return dataY.getCx();
                })
                .collect(Collectors.toList());
    }

    private static boolean isOneToMany(String input) {
        return (Arrays.asList("c3","c5").contains(input));
    }

    // Shall I apply this to each element,and return list of 1 or list of many elements 
    private static Optional<List<String>> operationOneToMany(String input) {
        if ("c3".equals(input))
            return Optional.of(Arrays.asList("c31","c32","c33"));
        else if ("c5".equals(input))
            return Optional.of(Arrays.asList("c51","c52"));
        else
            return Optional.empty();
    }

}

顺便说一句，它不起作用

---

工作代码，但不确定是否经过优化

public class Test2 {
    public static void main(String[] args) {
        DataX dataX = new DataX("abc-123","c5"));
        System.out.println("dataX = " + dataX);

        List<DataY> collect = dataX.getC().stream()
                .map(c -> operationOneToMany(c))
                .flatMap(e -> e.stream())
                .map(c -> new DataY(dataX.getA(),c))
                .collect(Collectors.toList());

        System.out.println("collect = " + collect);
    }

    private static List<String> operationOneToMany(String input) {
        if ("c3".equals(input))
            return Arrays.asList("c31","c33");
        else if ("c5".equals(input))
            return Arrays.asList("c51","c52");
        else
            return Arrays.asList(input);
    }

}

解决方法

如@Rono所建议

public class Test2 {
    public static void main(String[] args) {
        DataX dataX = new DataX("abc-123",Arrays.asList("c1","c2","c3","c4","c5"));
        System.out.println("dataX = " + dataX);

        List<DataY> collect = dataX.getC().stream()
                .flatMap(e -> operationOneToMany(e).stream())
                .map(c -> new DataY(dataX.getA(),UUID.randomUUID().toString(),c))
                .collect(Collectors.toList());

        System.out.println("collect = " + collect);
    }

    private static List<String> operationOneToMany(String input) {
        if ("c3".equals(input))
            return Arrays.asList("c31","c32","c33");
        else if ("c5".equals(input))
            return Arrays.asList("c51","c52");
        else
            return Arrays.asList(input);
    }

}