How does PHP determine whether the returned data is in json format?

In development, it often involves the processing of data returned from interfaces or other data sources. Among them, processing JSON format data is a very common task. As a highly dynamically typed language, PHP provides a variety of built-in functions and extension libraries to process JSON format data. However, in actual development, we may face a problem, how to determine whether the returned data is in JSON format?

In this article, we will explore how to solve this problem using PHP.

1. What is JSON format?

Before we start discussing how to determine whether the returned data is JSON formatted, let us first understand the JSON format.

JSON is the abbreviation of JavaScript Object Notation (JavaScript Object Notation), which is a lightweight data exchange format. It is a text format that can be parsed and generated by any programming language. JSON data consists of key-value pairs, where the key is a string and the value can be a string, number, Boolean value, object, array and other data types.

The following is a simple JSON data example:

{
    "name": "John",
    "age": 30,
    "married": true,
    "pets": ["dog", "cat"]
}

2. How to determine whether the returned data is JSON formatted?

In PHP, we can use some built-in functions to determine whether the returned data is JSON formatted. The following are two common methods:

Method 1: Use json_decodeFunction

json_decode function is a built-in function in PHP that can convert JSON format strings into PHP variables. If the incoming string is not in valid JSON format, a NULL value will be returned.

We can use the following code to determine whether the returned data is in JSON format:

function isJson($string) {
    json_decode($string);
    return (json_last_error() == JSON_ERROR_NONE);
}

In this method, we first call the json_decode function to try to parse the JSON string. If the parsing fails, it means that the string is not JSON formatted.

Next, we call the json_last_error function to get the error code of the last call to the json_decode function. If JSON_ERROR_NONE is returned, the string is JSON formatted, otherwise it is not.

Method 2: Use the json_last_error function

json_last_error function is a built-in function in PHP that can obtain the error code that occurred last time JSON encoding and decoding occurred. If this function returns JSON_ERROR_NONE, it means that the incoming string is JSON formatted, otherwise it is not.

We can use the following code to determine whether the returned data is in JSON format:

function isJson($string) {
    return is_string($string) && is_array(json_decode($string, true)) && (json_last_error() == JSON_ERROR_NONE);
}

In this method, we first use the is_string function to determine whether the incoming value is String type. Next, we call the json_decode function to try to parse the JSON string and convert it into a PHP array. If this function returns an array and the return value of the json_last_error function is successful, it means that the incoming string is JSON formatted, otherwise it is not.

3. Summary

In this article, we discussed how to use PHP to determine whether the returned data is JSON formatted. We have introduced two common methods. The first is to use the json_decode function and the json_last_error function to judge. The second is to use the json_last_error function to judge. No matter which method is used, we can quickly determine whether the data is in JSON format for subsequent processing.

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