如何在 PHP 中解析嵌套数组中的 JSON 数据

Question

我正在努力从格式如下的 JSON 文件中检索一些值：

{
"@context": [
    "https://raw.githubusercontent.com/geojson/geojson-ld/master/contexts/geojson-base.jsonld",
    {
        "wx": "https://api.weather.gov/ontology#",
        "@vocab": "https://api.weather.gov/ontology#"
    }
],
"type": "FeatureCollection",
"features": [
    {
        "id": "https://api.weather.gov/alerts/NWS-IDP-PROD-2485131-2320093",
        "type": "Feature",
        "geometry": {
            "type": "Polygon",
            "coordinates": [
                [
                    [
                        -95.45,
                        32.36
                    ],
                    [
                        -96.07,
                        32.36
                    ],
                    [
                        -96.08,
                        32.76
                    ],
                    [
                        -95.92,
                        32.82
                    ],
                    [
                        -95.85,
                        32.77
                    ],
                    [
                        -95.77,
                        32.77
                    ],
                    [
                        -95.76,
                        32.75
                    ],
                    [
                        -95.71,
                        32.75
                    ],
                    [
                        -95.66,
                        32.71
                    ],
                    [
                        -95.64,
                        32.72
                    ],
                    [
                        -95.59,
                        32.68
                    ],
                    [
                        -95.6,
                        32.48
                    ],
                    [
                        -95.47,
                        32.37
                    ],
                    [
                        -95.45,
                        32.36
                    ]
                ]
            ]
        },
        "properties": {
            "@id": "https://api.weather.gov/alerts/NWS-IDP-PROD-2485131-2320093",
            "@type": "wx:Alert",
            "id": "NWS-IDP-PROD-2485131-2320093",
            "areaDesc": "Van Zandt",
            "geocode": {
                "UGC": [
                    "TXC467"
                ],
                "SAME": [
                    "048467"
                ]
            },
            "references": [],
            "sent": "2017-08-13T00:03:41+00:00",
            "effective": "2017-08-13T00:03:41+00:00",
            "onset": "2017-08-13T00:03:00+00:00",
            "expires": "2017-08-13T01:00:00+00:00",
            "ends": "2017-08-13T01:00:00+00:00",
            "status": "Actual",
            "messageType": "Alert",
            "category": "Met",
            "severity": "Severe",
            "certainty": "Observed",
            "urgency": "Immediate",
            "event": "Severe Thunderstorm Warning",
            "sender": "NWS Fort Worth TX",
            "headline": "Severe Thunderstorm Warning issued August 12 at 7:03PM CDT expiring August 12 at 8:00PM CDT by NWS Fort Worth TX",
            "description": "The National Weather Service in Fort Worth has issued a\n\n* Severe Thunderstorm Warning for...\nVan Zandt County in north central Texas...\n\n* Until 800 PM CDT.\n\n* At 703 PM CDT, a severe thunderstorm was located near Wills Point,\nmoving east at 25 mph.\n\nHAZARD...65 mph wind gusts and quarter size hail.\n\nSOURCE...Radar indicated.\n\nIMPACT...Hail damage to vehicles is expected. Expect wind damage\nto roofs, siding, and trees.\n\n* This severe thunderstorm will be near,\nCanton around 710 PM CDT.\nEdgewood around 715 PM CDT.\nFruitvale around 725 PM CDT.\nGrand Saline around 735 PM CDT.\nVan around 750 PM CDT.\n\nThis includes Interstate 20 between mile markers 513 and 542.",
            "instruction": "For your protection get inside a sturdy structure and stay away from\nwindows.\n\nContinuous cloud to ground lightning is occurring with this storm.\nMove indoors immediately. Lightning can kill.\n\nHeavy rainfall is occurring with this storm, and may lead to flash\nflooding. Do not drive your vehicle through flooded roadways.",
            "response": "Shelter",
            "parameters": {
                "eventMotionDescription": [
                    "2017-08-13T00:03:00.000-05:00...storm...277DEG...23KT...32.62,-95.97"
                ],
                "hailSize": [
                    "1.00"
                ],
                "windGust": [
                    65
                ],
                "tornadoDetection": [
                    "POSSIBLE"
                ],
                "VTEC": [
                    "/O.NEW.KFWD.SV.W.0313.170813T0003Z-170813T0100Z/"
                ],
                "EAS-ORG": [
                    "WXR"
                ],
                "PIL": [
                    "FWDSVRFWD"
                ],
                "BLOCKCHANNEL": [
                    "CMAS",
                    "EAS",
                    "NWEM"
                ],
                "eventEndingTime": [
                    "2017-08-13T01:00:00Z"
                ]
            }
        }
    },

我正在尝试从“属性”键下的键中获取值。我正在努力解决的是数组是否以嵌套在@context 或“功能”下的“属性”开头？我不熟悉使用 @ 键的 JSON 数据。

我需要更多的价值观。但是对于初学者来说，我只是使用嵌套在“功能”->“属性”下的事件键，其中大多数键是我需要的值。我没有得到输出。

    <?php

$url = 'http://stream.dfwstormforce.com/json/nat_alerts.json'; // path to your JSON file
$data = file_get_contents($url); // put the contents of the file into a variable
$result = json_decode($data, true); // decode the JSON feed


foreach($results as $result) {
    dump($result); //this will dump the array
    foreach($results['features'] as $data) {
        dump($data['event']);
    }
}

?>

-谢谢

编辑：为 json_decode 代码添加了建议

Answer 1

正如其他人所说，如果您希望结果是关联数组，则需要将 true 作为第二个参数传递给 json_decode。

层次结构是功能/属性/事件，因此您可以查看功能并从每个功能的属性中提取您想要的内容。

<?php
$url = 'http://stream.dfwstormforce.com/json/nat_alerts.json'; // path to your JSON file
$data = file_get_contents($url); // put the contents of the file into a variable
$results = json_decode($data, true); // decode the JSON feed

foreach($results['features'] as $currFeature)
{
    $currEvent = $currFeature['properties']['event'];
    echo $currEvent."\n";
}

Answer 2

使用json_decode($data, true)。 true 告诉 json_decode 返回嵌套的关联数组而不是对象。

Answer 3

正如 BarNakedCoder 所说： json_decode($data, true) 但你也需要更换

dump($data['event']

与：

dump($data[0]['event'])