(Transfer) Using JSON in PHP language, phpjson_PHP tutorial

(Transferred) Using JSON in PHP language, phpjson

Original text:

http://www.ruanyifeng.com/blog/2011/01/json_in_php.html

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Author: Ruan Yifeng

Date: January 14, 2011

At present, JSON has become one of the most popular data exchange formats, and almost all APIs of major websites support it.

I wrote an article "Data Types and JSON Format" to discuss its design ideas. Today, I would like to summarize the PHP language's support for it, which is what you must know to develop Internet applications (especially writing APIs).

Starting from version 5.2, PHP natively provides json_encode() and json_decode() functions, the former is used for encoding, and the latter is used for decoding.

1. json_encode()

This function is mainly used to convert arrays and objects into json format. Let’s first look at an example of array conversion:

$arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);
echo json_encode($arr);

The result is

　{"a":1,"b":2,"c":3,"d":4,"e":5}

Look at another example of object conversion:

$obj->body           = 'another post';
　　
$obj->id             = 21;
　　
$obj->approved       = true;
　　
$obj->favorite_count = 1;
　　
$obj->status         = NULL;
　　
echo json_encode($obj);

The result is

{
　　　　"body":"another post",
　　
　　　　"id":21,
　　
　　　　"approved":true,
　　
　　　　"favorite_count":1,
　　
　　　　"status":null
} 
　　

Since json only accepts utf-8 encoded characters, the parameters of json_encode() must be utf-8 encoded, otherwise you will get empty characters or null. When Chinese uses GB2312 encoding, or foreign languages ​​use ISO-8859-1 encoding, special attention should be paid to this point.

2. Index array and associative array

PHP supports two types of arrays, one is an indexed array that only stores "value" (value), and the other is an associative array that stores "name/value" (name/value) .

Since javascript does not support associative arrays, json_encode() only converts the indexed array to array format, and converts the associative array to object format.

For example, now there is an index array

$arr = Array('one', 'two', 'three');
　　
echo json_encode($arr);

The result is:

["one","two","three"] 

If you change it to an associative array:

$arr = Array('1'=>'one', '2'=>'two', '3'=>'three');
 　　
echo json_encode($arr);

The result changed:

{"1":"one","2":"two","3":"three"} 

Note that the data format has changed from "[]" (array) to "{}" (object).

If you need to force "index array" into "object", you can write like this

json_encode( (object)$arr );

or

json_encode ( $arr, JSON_FORCE_OBJECT );

3. Class conversion

The following is a PHP class:

class Foo {
　　
　　　　const     ERROR_CODE = '404';
　　
　　　　public    $public_ex = 'this is public';
　　
　　　　private   $private_ex = 'this is private!';
　　
　　　　protected $protected_ex = 'this should be protected'; 
 　　
　　　　public function getErrorCode() {
　　
　　　　　　return self::ERROR_CODE;
　　
　　　　}
　　
}
　　

Now, perform a json conversion on an instance of this class:

$foo = new Foo;
　　
$foo_json = json_encode($foo);
　　
echo $foo_json;

The output result is

{"public_ex":"this is public"} 

As you can see, except for public variables (public), other things (constants, private variables, methods, etc.) are missing.

4. json_decode()

This function is used to convert json text into the corresponding PHP data structure. Here is an example:

$json = '{"foo": 12345}';
 　　
$obj = json_decode($json);
　　
print $obj->{'foo'}; // 12345
　　

Normally, json_decode() always returns a PHP object, not an array. For example:

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
 　　
var_dump(json_decode($json));
　　

The result is a PHP object:

object(stdClass)#1 (5) {
　　
　　　　["a"] => int(1)
　　　　["b"] => int(2)
　　　　["c"] => int(3)
　　　　["d"] => int(4)
　　　　["e"] => int(5)
　　
}
　　

If you want to force the generation of PHP associative array, json_decode() needs to add a parameter true:

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
 　　
var_dump(json_decode($json,true));

The result is an associative array:

array(5) {
　　
　　 　　["a"] => int(1)
　　 　　["b"] => int(2)
　　 　　["c"] => int(3)
　　 　　["d"] => int(4)
　　 　　["e"] => int(5)
　　
}
　　

5. Common errors of json_decode()

The following three ways of writing json are all wrong. Can you see where the error is?

$bad_json = "{ 'bar': 'baz' }";
　　
$bad_json = '{ bar: "baz" }';
　　
$bad_json = '{ "bar": "baz", }';

Executing json_decode() on these three strings will return null and report an error.

The first error is that the json delimiter only allows the use of double quotes, not single quotes. The second mistake is that the "name" (the part to the left of the colon) of the json name-value pair must use double quotes in any case. The third error is that you cannot add a trailing comma after the last value.

In addition, json can only be used to represent objects and arrays. If json_decode() is used on a string or value, null will be returned.

var_dump(json_decode("Hello World")); //null

6. Reference Materials

[1] PHP Manual

[2] Ed Finkler, JSON is Everybody's Friend

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