java+json : how to get an element from a json object that contains an array of objects {[ {}, {}]}

Question

需要一些有关 java+json 的帮助。大家好!我需要按歌曲标题对数据进行排序并提供异常情况的处理。我需要编写对 json 文件中的数据进行排序的方法。例如，此方法还必须能够对具有相同字段的数据进行排序。该文件的解析有效。但它的结构如下:

{
    "musicAlbum": [
        {
            "groupname": "twenty one pilots",
            "songduration": 3.27,
            "songname": "Heathens"
        },
        {
            "groupname": "twenty one pilots",
            "songduration": 4.4,
            "songname": "Car Radio"
        },
        {
            "groupname": "Linkin Park",
            "songduration": 3.06,
            "songname": "Numb"
        }
    ]
}

我现在不知道如何从对象数组中获取任何元素。例如，当我尝试执行:.getSongName() 时，我得到“null”。

我有一个带有 String groupName 的 Record 类；字符串歌曲名称；和双倍歌曲持续时间；所有 getter 和 setter 。还有带有解析方法的 JsonParser 类。和 MusicAlbum 类与列表专辑。还有 main 类:

import java.io.IOException;
import java.util.List;

public class App {
public static void main(String[] args) throws IOException // exception to be 
handled
{
    List<Record> album = JsonParser.parseJson();
    System.out.println(album); 

    for (int i = 0; i < album.size(); i++) {
        System.out.println(album.get(i));
    }
    Record songName = new Record();
    System.out.println(songName); 
    System.out.println(songName.getSongName());

}
}

我现在在控制台中拥有的内容:

[MusicAlbum [album=[Record [groupName=twenty one pilots, songName=Heathens, songDuration=3.27] , Record [groupName=twenty one pilots, songName=Car Radio, songDuration=4.4] , Record [groupName=Linkin Park, songName=Numb, songDuration=3.06] , Record [groupName=Lana Del Rey, songName=Summertime sadness, songDuration=3.56] , Record [groupName=Imagine Dragons, songName=Thunder, songDuration=3.24] , Record [groupName=Three Days Grace, songName=Outsider, songDuration=2.43] , Record [groupName=ONUKA, songName=When I Met You, songDuration=4.04] , Record [groupName=Foster The People, songName=Best Friend, songDuration=4.25] , Record [groupName=Massive Attack, songName=Angel, songDuration=6.18] , Record [groupName=Florence + The Machine, songName=Big God, songDuration=4.28] , Record [groupName=Die antwoord, songName=banana brain, songDuration=7.12] , Record [groupName=Coldplay, songName=Hypnotised, songDuration=5.54] ]]]

MusicAlbum [album=[Record [groupName=twenty one pilots, songName=Heathens, songDuration=3.27] , Record [groupName=twenty one pilots, songName=Car Radio, songDuration=4.4] , Record [groupName=Linkin Park, songName=Numb, songDuration=3.06] , Record [groupName=Lana Del Rey, songName=Summertime sadness, songDuration=3.56] , Record [groupName=Imagine Dragons, songName=Thunder, songDuration=3.24] , Record [groupName=Three Days Grace, songName=Outsider, songDuration=2.43] , Record [groupName=ONUKA, songName=When I Met You, songDuration=4.04] , Record [groupName=Foster The People, songName=Best Friend, songDuration=4.25] , Record [groupName=Massive Attack, songName=Angel, songDuration=6.18] , Record [groupName=Florence + The Machine, songName=Big God, songDuration=4.28] , Record [groupName=Die antwoord, songName=banana brain, songDuration=7.12] , Record [groupName=Coldplay, songName=Hypnotised, songDuration=5.54] ]]

Record [groupName=null, songName=null, songDuration=0.0] 

null

我不知道该怎么做以及如何编写数据接收方法。

感谢您对此方法的任何帮助!

Answer 1

好吧，如果没有有关您的 Record 类和解析器的更多详细信息，我只能进行一些逆向工程。

这就是您的数据的样子。

MusicAlbum [
    album= [
        Record [groupName=twenty one pilots, songName=Heathens, songDuration=3.27] ,
        Record [groupName=twenty one pilots, songName=Car Radio, songDuration=4.4] ,
        Record [groupName=Linkin Park, songName=Numb, songDuration=3.06] ,
        Record [groupName=Lana Del Rey, songName=Summertime sadness, songDuration=3.56] ,
        Record [groupName=Imagine Dragons, songName=Thunder, songDuration=3.24] ,
        Record [groupName=Three Days Grace, songName=Outsider, songDuration=2.43] ,
        Record [groupName=ONUKA, songName=When I Met You, songDuration=4.04] ,
        Record [groupName=Foster The People, songName=Best Friend, songDuration=4.25] ,
        Record [groupName=Massive Attack, songName=Angel, songDuration=6.18] ,
        Record [groupName=Florence + The Machine, songName=Big God, songDuration=4.28] ,
        Record [groupName=Die antwoord, songName=banana brain, songDuration=7.12] , Record [groupName=Coldplay, songName=Hypnotised, songDuration=5.54]
    ]
]

MusicAlbum 有一个记录数组，每个记录都有一些字段，songName 就是其中之一。

因此，获取记录详细信息的整体算法如下所示:

List<Album> albums = parseJson("{...}");
for (Album album : albums) {
    // 'album' is a bad name here, it's storing records, not albums
    List<Record> records = album.getAlbum();
    for (Record record : records) {
        System.out.println(record.getSonName());
    }
}

这基本上是伪代码，它不会编译，只是为了给你一个想法。