PHP解析JSON数组的几种方法

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JSON（JavaScript Object Notation）作为一种轻量级的数据交换格式，在Web应用中被广泛用于前后端数据传输。在PHP中处理JSON数据是日常开发中的常见任务，尤其是当JSON结构中包含多层嵌套的数组时，如何高效、准确地读取这些数据成为了关键。

1. JSON数据结构概述

JSON数据主要由两种结构组成：

• 对象（Object）：由键值对组成，键是字符串，值可以是字符串、数字、布尔值、null、对象或数组。在PHP中通常被解析为关联数组。
• 数组（Array）：由有序的值列表组成，值可以是任意JSON数据类型。在PHP中通常被解析为索引数组。

当JSON中包含嵌套的对象和数组时，理解其层级关系对于正确解析至关重要。例如，以下JSON片段展示了典型的嵌套结构：

{
  "success": 1,
  "results": [
    {
      "Id": 202322021,
      "SportName": "Football",
      "HomeTeam": "Kayserispor",
      "optionMarkets": [
        {
          "name": {
            "value": "Match Result"
          },
          "options": [
            {
              "name": {
                "value": "Kayserispor"
              },
              "price": {
                "odds": 1.055
              }
            },
            {
              "name": {
                "value": "X"
              },
              "price": {
                "odds": 11
              }
            }
          ]
        },
        {
          "name": {
            "value": "Double Chance"
          },
          "options": [
            {
              "value": "Kayserispor or X"
            },
            {
              "value": "X or Artvin Hopaspor"
            }
          ]
        }
      ]
    }
  ]
}

在这个结构中，results是一个数组，其每个元素都是一个对象。每个对象内部又包含optionMarkets数组，而optionMarkets数组的每个元素又是一个对象，其中包含options数组，等等。

2. 使用 json_decode 解析JSON字符串

在PHP中，json_decode()函数是解析JSON字符串的核心工具。它将JSON格式的字符串转换为PHP变量。

函数签名：mixed json_decode ( string $json [, bool $associative = false [, int $depth = 512 [, int $options = 0 ]]] )

• $json：要解码的JSON字符串。
• $associative：如果设置为true，JSON对象将被转换为PHP关联数组；如果设置为false（默认），JSON对象将被转换为PHP stdClass对象。对于处理嵌套结构，通常建议设置为true以便于数组方式访问。

示例代码：

<?php
// 示例JSON字符串
$json_string = '{"success":1,"pager":{"page":1,"per_page":250,"total":1813},"results":[{"Id":202322021,"SportId":4,"SportName":"Football","RegionId":31,"RegionName":"Turkey","LeagueId":102729,"LeagueName":"Turkiye Kupasi","BetRadarId":29664196,"our_event_id":4157451,"IsPreMatch":true,"Date":"2021-10-27T17:45:00Z","updated_at":"1635354806","HomeTeam":"Kayserispor","HomeTeamId":230391,"AwayTeam":"Artvin Hopaspor","AwayTeamId":228914,"Markets":[],"optionMarkets":[{"properties":[],"comboPrevention":"NoFixtureCombo","templateCategory":{"category":"Gridable","id":0},"status":"Visible","isMain":true,"grouping":{"gridGroups":["ls8o6ll2v"],"detailed":[{"name":"Match Result","marketTabId":1,"marketHelpPath":"Football\/Match Result (Regular Time)","index":7930,"displayType":"Regular","group":0}],"parameters":{"marketType":"ThreeWay","period":"RegularTime","happening":"Goal"}},"id":29622716,"name":{"value":"Match Result","sign":"9Vlc5w=="},"minCombo":1,"options":[{"name":{"value":"Kayserispor","sign":"tyg4wg=="},"id":96896088,"sourceName":{"value":"1"},"status":"Visible","price":{"id":145532907,"odds":1.055,"americanOdds":-2000,"denominator":18,"numerator":1}},{"price":{"id":145532911,"odds":11,"americanOdds":1000,"numerator":10,"denominator":1},"status":"Visible","name":{"value":"X","sign":"JHhicw=="},"id":96896089},{"price":{"id":145532915,"odds":31,"americanOdds":3000,"numerator":30,"denominator":1},"status":"Visible","sourceName":{"value":"2"},"id":96896090,"name":{"value":"Artvin Hopaspor","sign":"2ruL4g=="}}],"parameters":[{"key":"Happening","value":"Goal","type":"String"},{"key":"MarketType","value":"3way","type":"String"},{"type":"String","value":"RegularTime","key":"Period"}]},{"minCombo":1,"id":29622721,"name":{"value":"Double Chance","sign":"WRDxhg=="},"parameters":[{"key":"Happening","type":"String","value":"Goal"},{"key":"MarketType","value":"DoubleChance","type":"String"},{"type":"String","value":"RegularTime","key":"Period"}],"options":[{"status":"Suspended","price":{"odds":1,"id":145532955},"id":96896100,"name":{"sign":"YrFHYg==","value":"Kayserispor or X"}},{"name":{"value":"X or Artvin Hopaspor","sign":"knPxTA=="},"id":96896101,"status":"Visible","price":{"americanOdds":825,"denominator":4,"numerator":33,"id":145532959,"odds":9.25}},{"price":{"id":145532963,"odds":1.04,"americanOdds":-2500,"numerator":1,"denominator":25},"status":"Visible","name":{"sign":"fwDTwg==","value":"Kayserispor or Artvin Hopaspor"},"id":96896102}],"comboPrevention":"NoFixtureCombo","properties":[],"isMain":false,"status":"Visible","templateCategory":{"id":0,"category":"Gridable"},"grouping":{"parameters":{"period":"RegularTime","marketType":"DoubleChance","happening":"Goal"},"detailed":[{"marketTabId":1,"name":"Double Chance","group":0,"displayType":"Regular","marketHelpPath":"Football\/Double Chance","index":17230}],"gridGroups":["e8vi2hdwz"]}},{"options":[{"price":{"numerator":87,"denominator":100,"americanOdds":-115,"odds":1.87,"id":155223689},"status":"Visible","name":{"sign":"5Rageg==","value":"Over 3,5"},"id":100328998},{"price":{"numerator":5,"denominator":6,"americanOdds":-120,"odds":1.83,"id":155223693},"status":"Visible","id":100328999,"name":{"value":"Under 3,5","sign":"KP8xUw=="}}],"parameters":[{"type":"Decimal","value":"3.5000","key":"DecimalValue"},{"key":"Happening","value":"Goal","type":"String"},{"type":"String","value":"Over\/Under","key":"MarketType"},{"key":"Period","type":"String","value":"RegularTime"}],"name":{"value":"Total Goals","sign":"Y9HR2w=="},"id":30811485,"minCombo":1,"spread":0.04,"grouping":{"parameters":{"period":"RegularTime","marketType":"OverUnder","attr":"3.5000","happening":"Goal","attrType":"Decimal"},"detailed":[{"name":"Over\/Under Total Goals","marketTabId":1,"subIndex":4,"displayType":"OverUnder","index":27330,"group":0},{"subIndex":4,"marketTabId":1,"group":0,"displayType":"OverUnder","index":35130},{"group":2,"displayType":"OverUnder","index":11730,"subIndex":4,"marketTabId":1,"name":"Over\/Under Total Goals"},{"index":19530,"displayType":"OverUnder","group":2,"marketTabId":1,"subIndex":4}],"gridGroups":["tabpo1c9n"]},"balanced":1,"status":"Visible","attr":"3,5","isMain":false,"templateCategory":{"category":"Gridable","id":0},"properties":[],"comboPrevention":"NoFixtureCombo"}]}]}';

$json_data = json_decode($json_string, true);

// 检查解码是否成功
if (json_last_error() !== JSON_ERROR_NONE) {
    echo "JSON解码错误: " . json_last_error_msg() . "\n";
    exit;
}

// 访问顶层数据
echo "Success: " . $json_data['success'] . "\n";
echo "Total Results: " . $json_data['pager']['total'] . "\n";
?>

3. 遍历和访问嵌套数组

一旦JSON字符串被解码为PHP关联数组，就可以使用标准的数组访问语法（[]）和循环结构（foreach）来遍历和提取嵌套数据。

以前面的JSON数据为例，我们将演示如何读取results数组中的每个比赛信息，并进一步深入读取每个比赛的optionMarkets及其options。

<?php
// ... (接上文的 $json_string 和 $json_data 定义) ...

if (!empty($json_data['results'])) {
    foreach ($json_data['results'] as $event) {
        // 访问直接属性
        echo "----------------------------------------\n";
        echo "比赛ID: " . $event['Id'] . "\n";
        echo "运动类型: " . $event['SportName'] . "\n";
        echo "主队: " . $event['HomeTeam'] . "\n";
        echo "客队: " . $event['AwayTeam'] . "\n";
        echo "联赛名称: " . $event['LeagueName'] . "\n";
        echo "日期: " . $event['Date'] . "\n";

        // 访问 optionMarkets 数组
        if (!empty($event['optionMarkets'])) {
            echo "  市场选项 (optionMarkets):\n";
            foreach ($event['optionMarkets'] as $market) {
                // 访问市场名称
                $market_name = isset($market['name']['value']) ? $market['name']['value'] : 'N/A';
                echo "    - 市场名称: " . $market_name . "\n";

                // 访问 options 数组
                if (!empty($market['options'])) {
                    echo "      选项 (options):\n";
                    foreach ($market['options'] as $option) {
                        $option_name = isset($option['name']['value']) ? $option['name']['value'] : 'N/A';
                        $option_price = isset($option['price']['odds']) ? $option['price']['odds'] : 'N/A';
                        echo "        -> 名称: " . $option_name . ", 赔率: " . $option_price . "\n";
                    }
                } else {
                    echo "      无可用选项。\n";
                }
            }
        } else {
            echo "  无可用市场选项。\n";
        }
    }
} else {
    echo "JSON数据中没有 'results' 数组或其为空。\n";
}
?>

代码解析：

1. 首先通过$json_data['results']访问到顶层的results数组。
2. 使用第一个foreach循环遍历results数组中的每一个比赛事件（$event）。
3. 在每个$event内部，直接访问HomeTeam、AwayTeam等简单键值。
4. 为了访问optionMarkets这个嵌套数组，我们再次使用if (!empty(...))进行存在性检查，然后使用第二个foreach循环遍历optionMarkets中的每个市场（$market）。
5. 同理，对于options数组，也进行存在性检查，并使用第三个foreach循环遍历每个选项（$option）。
6. 在访问深层嵌套的值（如$market['name']['value']和$option['price']['odds']）时，务必进行isset()或empty()检查，以避免在某些键不存在时产生PHP警告或错误。

4. 使用 RecursiveArrayIterator 进行深度遍历

对于结构深度不确定或需要通用遍历所有键值对的场景，PHP的RecursiveArrayIterator和RecursiveIteratorIterator提供了一种更优雅的解决方案。它们允许你以递归方式遍历多维数组，而无需手动编写多层嵌套循环。

<?php
// ... (接上文的 $json_string 和 $json_data 定义) ...

echo "\n--- 使用 RecursiveArrayIterator 遍历所有键值对 ---\n";

// 将解码后的数据放入一个ArrayObject，以便RecursiveArrayIterator使用
$data_obj = new ArrayObject($json_data);

// 创建RecursiveIteratorIterator实例，它将遍历RecursiveArrayIterator生成的所有元素
$iterator = new RecursiveIteratorIterator(
    new RecursiveArrayIterator($data_obj)
);

foreach ($iterator as $key => $value) {
    // 获取当前元素的深度，用于格式化输出
    $depth = $iterator->getDepth();
    echo str_repeat("  ", $depth) . $key . ": " . (is_array($value) ? "Array" : $value) . "\n";
}
?>

代码解析：

1. new ArrayObject($json_data)：将PHP数组包装成一个ArrayObject，这是RecursiveArrayIterator的构造函数所接受的类型。
2. new RecursiveArrayIterator($data_obj)：创建一个递归数组迭代器，它知道如何深入遍历数组的子元素。
3. new RecursiveIteratorIterator(...)：这是一个外部迭代器，它接受一个递归迭代器作为参数，并将其扁平化，使其可以像单层数组一样被foreach遍历。getDepth()方法可以获取当前元素的嵌套深度。
4. 这种方法适用于需要检查JSON中所有键值对的场景，但如果只需要特定路径下的数据，手动遍历可能更直接。

5. 注意事项与最佳实践

• JSON有效性验证：在json_decode之前或之后，始终使用json_last_error()和json_last_error_msg()检查JSON字符串是否有效以及解码过程中是否发生错误。无效的JSON字符串会导致json_decode返回null。
• 键的存在性检查：在访问数组元素之前，使用isset()或array_key_exists()检查键是否存在，尤其是在处理来自外部源的JSON数据时，以防止因键缺失而导致的PHP通知或错误。
• 性能考量：对于非常大的JSON字符串（几十MB甚至更大），json_decode会一次性将整个字符串加载到内存中。如果内存成为瓶颈，可能需要考虑使用流式解析器（如json_stream库）来逐块处理JSON数据。
• 数据类型转换：json_decode会尝试将JSON值转换为相应的PHP类型（例如，JSON数字转换为PHP整数或浮点数，JSON布尔值转换为PHP布尔值）。了解这些转换有助于避免意外的数据类型问题。
• 编码问题：确保JSON字符串的编码是UTF-8，并且PHP脚本的编码设置也正确，以避免中文或其他非ASCII字符乱码。

总结

在PHP中读取JSON中的数组数据，核心在于理解JSON的嵌套结构，并结合json_decode()函数将其转换为PHP关联数组。通过多层foreach循环可以精确地访问特定路径下的数据，而RecursiveArrayIterator则为深度或通用遍历提供了强大的工具。在实际开发中，务必结合错误处理和键存在性检查，以确保代码的健壮性和稳定性。掌握这些技巧，将使你能够高效地处理各种复杂的JSON数据。

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