The method to verify whether a string is legal in PHP is to use json_decode to judge the parsing result with json_last_error. The specific steps are as follows: 1. Use json_decode to try parsing the string; 2. Check whether there is an error through json_last_error. If you return JSON_ERROR_NONE, it means that it is legal; 3. For empty strings or simple values such as "null", you need to judge the type according to business needs; 4. If the expected result is an array, you can add is_array verification; 5. When processing unreliable input, it is recommended to use trim to remove the whitespace, and note that single quotes should be replaced with double quotes.
Sometimes you get a string, not sure if it is a legitimate JSON format, especially when dealing with API interfaces or user input. In PHP, there are actually relatively simple and reliable ways to verify this.
Use json_decode to judge
The json_decode function that comes with PHP can try to parse whether a string is legal JSON. If parsing fails, it means that the string is not a valid JSON.
You can write this way:
function is_valid_json($string) {
json_decode($string);
return json_last_error() === JSON_ERROR_NONE;
} The core of this method is: first try parsing with json_decode , and then check whether there are errors through json_last_error() . If there is no error, it means it is a legal JSON.
Some common mistakes include:
-
JSON_ERROR_SYNTAX: Syntax errors, such as mismatch in brackets, unclosed quotes, etc. -
JSON_ERROR_UTF8: Encoding issues, such as strings containing illegal UTF-8 characters.
Pay attention to handling null values and arrays
Sometimes, json_decode can successfully parse even an empty string, or a simple value like "null" or "true" , but it may not meet your business needs.
for example:
- An empty string
""will be considered not a legitimate JSON. - The string
"null"is a legal JSON value. - If you want to make sure it is an object or array, you also need to judge the type additionally.
So if you want this JSON to end up being an array or object, you can add the type to judge:
function is_valid_json_and_assoc($string) {
$result = json_decode($string, true);
return json_last_error() === JSON_ERROR_NONE && is_array($result);
}This ensures that the parsed result is an array (rather than a scalar value or other types).
Tips for handling original input
When the data source you want to check is unreliable, such as from user submissions or third-party interfaces, it is recommended to do basic filtering first, such as removing the beginning and end blank characters:
$string = trim($string);
Because sometimes extra spaces or newlines can cause parsing to fail, and these characters themselves do not affect the content of JSON.
Another small detail is: if the input looks like JSON, but uses single quotes, such as '{"name": "John"}' , this format will also be considered illegal by json_decode in PHP. At this time, you need to replace the single quotes with double quotes in advance, or prompt the user to correct the format.
Basically that's it. Just remember that the core method is json_decode json_last_error , and the rest are supplementary judgments based on actual scenarios.
The above is the detailed content of How to check if a string is valid JSON in PHP. For more information, please follow other related articles on the PHP Chinese website!
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