使用可选字段解析 JSON

Question

我正在尝试在 android studio 中解析一个包含以下内容的 JSON：

"stops": 
[
    {
        "num": 1,
        "time": "2016-04-27T06:15:00.000Z",
        "title":"Flight to London",
        "desc":"Barcelona BCN-London-Gatwick LGW",
        "type":"0",
        "subtype":0
    },
    {
        "num": 2,
        "time": "2016-04-27T10:35:00.000Z",
        "title":"Gatwick express",
        "desc":"From Airport to London",
        "type":"0",
        "subtype":1
    },
    {
        "num": 3,
        "time": "2016-04-27T12:15:00.000Z",
        "title":"Pub the black horse",
        "desc":"From Airport to London",
        "type":1,
        "subtype":1,
        "location": "51.476334, -0.062700",
        "images": [                 "https://fitzrovianews.files.wordpress.com/2011/01/black_horse_rathbone_pl.jpg" 
        ]               
    },
    {
        "num": 4,
        "time": "2016-04-27T12:16:47.000Z",
        "title":"The Tower Bridge",
        "desc":"# The Tower Bridge Facts\n## Architecture\n**Tower Bridge** is a combined bascule and suspension bridge in London built in _1886–1894_. The bridge crosses the River Thames close to the Tower of London and has become an iconic symbol of London. Tower Bridge is one of five London bridges now owned and maintained by the Bridge House Estates, a charitable trust overseen by the City of London Corporation. \n>It is the only one of the Trust's bridges not to connect the City of London directly to the Southwark bank, as its northern landfall is in Tower Hamlets.\n## The bridge Exhibition\nThis must-see London attraction invites you to step inside the most famous bridge in the world to explore its iconic structure, spectacular views and glass floor, modern exhibitions and magnificent Victorian Engine Rooms! ",
        "type":1,
        "subtype":6,
        "location": "51.507792, -0.087786",
        "images": [                 
"https://i.ytimg.com/vi/nby0Mr2LfBQ/hqdefault.jpg",
"http://raindropsofsapphire.com/wp-content/uploads/2011/10/london-bridge.jpg",
"http://www.londonforfree.net/gizmo/wp-content/uploads/2015/02/southwark-bridge.jpg"
        ]               
    },
    {
        "num": 5,
        "time": "2016-04-27T12:18:10.000Z",
        "title":"St. Paul Cathedral",
        "desc":"# HISTORY \nSt **Paul's Cathedral**, London, is an _Anglican cathedral_, the seat of the _Bishop of London_ and the mother church of the Diocese of London.  \n * It sits on Ludgate Hill at the highest point of the City of London and is a Grade 1 listed building. \n * Its dedication to Paul the Apostle dates back to the original church on this site, founded in AD 604.",
        "type":1,
        "subtype":6,
        "location": "51.513825, -0.098351",
        "images": [                 
"https://d1wgio6yfhqlw1.cloudfront.net/sysimages/product/resized6/Interior_St_Pauls_Cathedral_132_12992.jpg",
"https://d1kioxk2jrdjp.cloudfront.net/resized/486x324/48-st_pauls_ctahedral_millenirm_bridge.jpg",
"http://i4.mirror.co.uk/incoming/article8299330.ece/ALTERNATES/s615b/LOND-2016-052-HMQ-St-Pauls-Thanks-Giving-704JPG.jpg"
        ]               
    }
] 

问题是，我不知道如何处理可选的“位置”或“图像”字段。我知道如何处理第一个“停止”，我正在这样做：

JSONArray stops = jsonObj.getJSONArray("stops");

        for (int i = 0; i < stops.length(); i++) {
            JSONObject c = stops.getJSONObject(i);

            String num = c.getString("num");
            String time = c.getString("time");
            String title = c.getString("title");
            String descripcion = c.getString("desc");
            String type = c.getString("type");
            String subtype = c.getString("subtype");
......

}

但我不知道如何在这里检查它是一个元素位置还是一个 jsonArray“图像”......

Answer 1

处理 JSON 中可选字段的最佳方法是使用opt而不是get

如果请求的键不存在，则 opt 提供解析值（如果存在）或该数据类型的默认值。

最好的事情是，它甚至不需要 try catch 块，因为它总是返回一个值，并且在服务器出现任何错误的情况下，它不会让您的应用程序崩溃或阻止其他值被解析。

String location = response.optString("location");

如果 location 存在于响应中，则它将使用该值进行初始化，或者将字符串保留为空。在 int 或 long 的情况下默认为 0，在 boolean 的情况下默认为 false。阅读关于选择更多详细信息。