The situation is simple: I have a list of object List<ParentClass> list and would like to convert it to Map<orderKey, price>,java,java-stream"/>

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The situation is simple: I have a list of object List<ParentClass> list and would like to convert it to Map<orderKey, price>

java - Java 8 转换列表 to Map using the fields of the object's children?

The situation is simple: I have a list of object List<ParentClass> list and would like to convert it to Map<orderKey, price>

问题描述

The situation is simple: I have a list of object List<ParentClass> list and would like to convert it to Map<orderKey, price>

The class looks like the following

class ParentClass{
   Child1Class a;
   Child2Class b;
}

The orderKey class looks like this

class orderKey{
   String id;
   String itemName;
}

The children classes look like this

class Child1Class{
   String id;
   String itemName;
   Date date;
   .....
}

class Child2Class{
   BigDecimal price;
   ....
}

All of the classes have corresponded getters and setters for each field. So I essentially want to map the fields of the children's fields. How can I do this? 

-----------------------------MY ATTEMPT IS SOMETHING LIKE THIS--------------------------------------
list.stream().
.collect(Collectors
.toMap(ParentClass::getA, ParentClass::getB)
.entrySet().stream()
......
then I'm stuck

Not sure how I can construct the temp object orderKey as the key for the new map. Any help would be appreciated.

May be this not related directly to your situation, using this we can pick/sort/filter based on file extensions. this code, at-present extract .jpg/.jpeg extension files

package main

import (
    "fmt"
    "os"
    "path/filepath"
)

func main() {

    filepath.Walk("../searchStartFromWhere/", func(path string, info os.FileInfo, err error) error {
        if info.IsDir() {
            return nil
        }

        ext := filepath.Ext(path)
        switch ext {
        case ".jpg", ".jpeg": // Add more switch cases if required 
            fmt.Println(path)
        }
        return nil
    })
}

标签： javajava-stream

解决方案

像这样试试。由于您没有提供吸气剂，因此我不得不访问这些字段。它还假定一个OrderKey构造函数。

Map<OrderKey,BigDecimal> map = list
               .stream()
               .collect(Collectors
                         .toMap(parent ->
                             new OrderKey(parent.a.id,
                                  parent.a.itemName),
                          parent->parent.b.price));

，getters它看起来像这样。

    Map<OrderKey,BigDecimal> map=   
        list.stream()
            .collect(Collectors
                .toMap(parent ->
                      new OrderKey(parent.getA().getId(),
                                   parent.getA().getItemName()),
                       parent->parent.getB().getPrice()));

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