只需添加这个条件:

check if the type is string and then json decode <?php $subject = ['description' => '200 extra contacts','value' => '15','product_code' => 'OS_CONT12']; $subject = '{"description":"200 extra contacts","value":15,"product_code":"OS_CONT12"}'; if(gettype($subject) == 'string'){ $data = json_decode($subject, true); print_r($data); } else{ print_r("saurabh kasmble"); } ?> OUTPUT : Array ( [description] => 200 extra contacts [value] => 15 [product_code] => OS_CONT12 )

应该是这样的:

 function isJson($string)
 {
    // 1. Speed up the checking & prevent exception throw when non string is passed
    if (is_numeric($string) ||
        !is_string($string) ||
        !$string) {
        return false;
    }

    $cleaned_str = trim($string);
    if (!$cleaned_str || !in_array($cleaned_str[0], ['{', '['])) {
        return false;
    }

    // 2. Actual checking
    $str = json_decode($string);
    return (json_last_error() == JSON_ERROR_NONE) && $str && $str != $string;
}

单元测试

public function testIsJson()
{
    $non_json_values = [
        "12",
        0,
        1,
        12,
        -1,
        '',
        null,
        0.1,
        '.',
        "''",
        true,
        false,
        [],
        '""',
        '[]',
        '   {',
        '   [',
    ];

   $json_values = [
        '{}',
        '{"foo": "bar"}',
        '[{}]',
        '  {}',
        ' {}  '
    ];

   foreach ($non_json_values as $non_json_value) {
        $is_json = isJson($non_json_value);
        $this->assertFalse($is_json);
    }

    foreach ($json_values as $json_value) {
        $is_json = isJson($json_value);
        $this->assertTrue($is_json);
    }
}

使用PHPBench和下面的类，得到了以下结果:

<?php

declare(strict_types=1);

/**
 * @Revs(1000)
 * @Iterations(100)
 */
class BenchmarkJson
{
    public function benchCatchValid(): bool
    {
        $validJson = '{"validJson":true}';
        try {
            json_decode($validJson, true, 512, JSON_THROW_ON_ERROR);
            return true;
        } catch(\JsonException $exception) {}
        return false;
    }

    public function benchCatchInvalid(): bool
    {
        $invalidJson = '{"invalidJson"';
        try {
            json_decode($invalidJson, true, 512, JSON_THROW_ON_ERROR);
            return true;
        } catch(\JsonException $exception) {}
        return false;
    }

    public function benchLastErrorValid(): bool
    {
        $validJson = '{"validJson":true}';
        json_decode($validJson, true);
        return (json_last_error() === JSON_ERROR_NONE);
    }

    public function benchLastErrorInvalid(): bool
    {
        $invalidJson = '{"invalidJson"';
        json_decode($invalidJson, true);
        return (json_last_error() === JSON_ERROR_NONE);
    }

    public function benchNullValid(): bool
    {
        $validJson = '{"validJson":true}';
        return (json_decode($validJson, true) !== null);
    }

    public function benchNullInvalid(): bool
    {
        $invalidJson = '{"invalidJson"';
        return (json_decode($invalidJson, true) !== null);
    }
}

6 subjects, 600 iterations, 6,000 revs, 0 rejects, 0 failures, 0 warnings
(best [mean mode] worst) = 0.714 [1.203 1.175] 1.073 (μs)
⅀T: 721.504μs μSD/r 0.089μs μRSD/r: 7.270%
suite: 1343ab9a3590de6065bc0bc6eeb344c9f6eba642, date: 2020-01-21, stime: 12:50:14
+---------------+-----------------------+-----+------+-----+------------+---------+---------+---------+---------+---------+--------+-------+
| benchmark     | subject               | set | revs | its | mem_peak   | best    | mean    | mode    | worst   | stdev   | rstdev | diff  |
+---------------+-----------------------+-----+------+-----+------------+---------+---------+---------+---------+---------+--------+-------+
| BenchmarkJson | benchCatchValid       | 0   | 1000 | 100 | 2,980,168b | 0.954μs | 1.032μs | 1.016μs | 1.428μs | 0.062μs | 6.04%  | 1.33x |
| BenchmarkJson | benchCatchInvalid     | 0   | 1000 | 100 | 2,980,184b | 2.033μs | 2.228μs | 2.166μs | 3.001μs | 0.168μs | 7.55%  | 2.88x |
| BenchmarkJson | benchLastErrorValid   | 0   | 1000 | 100 | 2,980,184b | 1.076μs | 1.195μs | 1.169μs | 1.616μs | 0.083μs | 6.97%  | 1.54x |
| BenchmarkJson | benchLastErrorInvalid | 0   | 1000 | 100 | 2,980,184b | 0.785μs | 0.861μs | 0.863μs | 1.132μs | 0.056μs | 6.54%  | 1.11x |
| BenchmarkJson | benchNullValid        | 0   | 1000 | 100 | 2,980,168b | 0.985μs | 1.124μs | 1.077μs | 1.731μs | 0.114μs | 10.15% | 1.45x |
| BenchmarkJson | benchNullInvalid      | 0   | 1000 | 100 | 2,980,184b | 0.714μs | 0.775μs | 0.759μs | 1.073μs | 0.049μs | 6.36%  | 1.00x |
+---------------+-----------------------+-----+------+-----+------------+---------+---------+---------+---------+---------+--------+-------+

结论:检查json是否有效的最快方法是返回json_decode($json, true) !== null)。

2023年的今天,时代的回答:

虽然PHP 8.3仍在开发中，将提供新的内存效率高的json_validate()函数，但由于神奇的Symfony Polyfill组件，您可以在较旧的PHP版本(7.1和更新的版本)中使用它。

只需将以下包添加到您的项目:

composer require symfony/polyfill-php83

并在应用程序中使用它:

if (json_validate($data)) {
  // do sometihng
}

由于这种方法，您可以在旧的应用程序中使用新的PHP特性，并且在将来无需任何代码更改就可以迁移到PHP 8.3，因为当内置函数可用时，您的代码将自动使用它。

function is_json($input) {

    $input = trim($input);

    if (substr($input,0,1)!='{' OR substr($input,-1,1)!='}')
        return false;

    return is_array(@json_decode($input, true));
}

使用json_decode“探测”它实际上可能不是最快的方法。如果它是一个嵌套很深的结构，那么实例化大量数组对象来丢弃它们是浪费内存和时间。

所以使用preg_match和RFC4627正则表达式来确保有效性可能会更快:

  // in JS:
  var my_JSON_object = !(/[^,:{}\[\]0-9.\-+Eaeflnr-u \n\r\t]/.test(
         text.replace(/"(\\.|[^"\\])*"/g, '')));

在PHP中也一样:

  return !preg_match('/[^,:{}\\[\\]0-9.\\-+Eaeflnr-u \\n\\r\\t]/',
       preg_replace('/"(\\.|[^"\\\\])*"/', '', $json_string));

不过，我不是一个性能爱好者，不会在这里费心进行基准测试。