使用Java 8按属性对自定义对象列表进行分组 [英] Grouping the custom object list by properties using Java 8

问题描述

我正在学习lambda的许多新功能，并且想知道如何基于某些属性作为键将自定义对象列表分组? 例如，我在json中有这样的对象列表.

I am learning many new features of lambda and wondering how can I group by my custom object list based on certain properties as key? For example, I have list of object like this in json.

[{ "account" : "checking", "source" : "BOA" }, { "account" : "checking", "source" : "TD" }, { "account" : "saving", "source" : "WS" } ]

[{ "account" : "checking", "source" : "BOA" }, { "account" : "checking", "source" : "TD" }, { "account" : "saving", "source" : "WS" } ]

我正在寻找使用Java 8功能进行分组以获取这样的输出的方式(将源分组为逗号分隔的同一帐户.

I am looking for way to group using java 8 feature to get output like this (grouping source as comma separated for same account.

[{ "account" : "checking", "source" : "BOA, TD" }, { "account" : "saving", "source" : "WS" } ]

[{ "account" : "checking", "source" : "BOA, TD" }, { "account" : "saving", "source" : "WS" } ]

谢谢

推荐答案

该解决方案如何

    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;
    import java.util.stream.Collectors;

    public class Data {

        public static void main(String ab[]) {
            List<Data> dataList = Arrays.asList(new Data("checking", "BOA"), new Data("checking", "TD")
                    , new Data("saving", "WS"));
            List<Data> newList = new ArrayList<>(dataList.stream()
            .collect(Collectors.toMap(Data::getAccount, d -> d, (d1, d2) -> new Data(d1.account, d1.source + ", " + d2.source)))
            .values());
            System.out.println("dataList = " + dataList);
            System.out.println("newList = " + newList);
        }

        private String account;
        private String source;

        Data(String account, String source) {
            this.account = account;
            this.source = source;
        }

        @Override
        public String toString() {//just override toString as json object with out using jon passer  
            return "{ \"account\" : \""+account+"\", \"source\" : \""+source+"\" }";
        }

        public String getAccount() {
            return account;
        }

        public void setAccount(String account) {
            this.account = account;
        }

        public String getSource() {
            return source;
        }

        public void setSource(String source) {
            this.source = source;
        }
    }

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