Currently, 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:
<ol class="dp-c"> <li class="alt"><span><span class="vars">$arr</span><span> = </span><span class="keyword">array</span><span> (</span><span class="string">'a'</span><span>=>1,</span><span class="string">'b'</span><span>=>2,</span><span class="string">'c'</span><span>=>3,</span><span class="string">'d'</span><span>=>4,</span><span class="string">'e'</span><span>=>5); </span></span></li> <li> <span class="func">echo</span><span> json_encode(</span><span class="vars">$arr</span><span>); </span> </li> </ol>
and the result is
<ol class="dp-c"><li class="alt"><span><span>{</span><span class="string">"a"</span><span>:1,</span><span class="string">"b"</span><span>:2,</span><span class="string">"c"</span><span>:3,</span><span class="string">"d"</span><span>:4,</span><span class="string">"e"</span><span>:5} </span></span></li></ol>. Then look at an example of object conversion:
<ol class="dp-c"> <li class="alt"><span><span class="vars">$obj</span><span>->body = </span><span class="string">'another post'</span><span>; </span></span></li> <li> <span class="vars">$obj</span><span>->id = 21; </span> </li> <li class="alt"> <span class="vars">$obj</span><span>->approved = true; </span> </li> <li> <span class="vars">$obj</span><span>->favorite_count = 1; </span> </li> <li class="alt"> <span class="vars">$obj</span><span>->status = NULL; </span> </li> <li> <span class="func">echo</span><span> json_encode(</span><span class="vars">$obj</span><span>); </span> </li> </ol>
and the result is
<ol class="dp-c">
<li class="alt"><span><span>{ </span></span></li>
<li>
<span class="string">"body"</span><span>:</span><span class="string">"another post"</span><span>, </span>
</li>
<li class="alt">
<span class="string">"id"</span><span>:21, </span>
</li>
<li>
<span class="string">"approved"</span><span>:true, </span>
</li>
<li class="alt">
<span class="string">"favorite_count"</span><span>:1, </span>
</li>
<li>
<span class="string">"status"</span><span>:null </span>
</li>
<li class="alt"><span>} </span></li>
</ol>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. Indexed arrays and associative arrays
PHP supports two types of arrays, one is an indexed array that only stores "value" (value), The other is an associative array that stores name/value pairs.
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
<ol class="dp-c"> <li class="alt"><span><span class="vars">$arr</span><span> = Array(</span><span class="string">'one'</span><span>, </span><span class="string">'two'</span><span>, </span><span class="string">'three'</span><span>); </span></span></li> <li> <span class="func">echo</span><span> json_encode(</span><span class="vars">$arr</span><span>); </span> </li> </ol>
and the result is:
<ol class="dp-c"><li class="alt"><span><span>[</span><span class="string">"one"</span><span>,</span><span class="string">"two"</span><span>,</span><span class="string">"three"</span><span>] </span></span></li></ol>
If you change it to an associative array:
<ol class="dp-c"> <li class="alt"><span><span class="vars">$arr</span><span> = Array(</span><span class="string">'1'</span><span>=></span><span class="string">'one'</span><span>, </span><span class="string">'2'</span><span>=></span><span class="string">'two'</span><span>, </span><span class="string">'3'</span><span>=></span><span class="string">'three'</span><span>); </span></span></li> <li> <span class="func">echo</span><span> json_encode(</span><span class="vars">$arr</span><span>); </span> </li> </ol>
The result changes:
<ol class="dp-c"><li class="alt"><span><span>{</span><span class="string">"1"</span><span>:</span><span class="string">"one"</span><span>,</span><span class="string">"2"</span><span>:</span><span class="string">"two"</span><span>,</span><span class="string">"3"</span><span>:</span><span class="string">"three"</span><span>} </span></span></li></ol>Note that the data format changes from "[]" (array) to "{}" (object).
If you need to force "index array" into "object", you can write like this
<ol class="dp-c"><li class="alt"><span><span>json_encode( (object)</span><span class="vars">$arr</span><span> ); </span></span></li></ol>
or
<ol class="dp-c"><li class="alt"><span><span>json_encode ( </span><span class="vars">$arr</span><span>, JSON_FORCE_OBJECT ); </span></span></li></ol>
3. Class ( class) conversion
The following is a PHP class:
<ol class="dp-c">
<li class="alt"><span><span class="keyword">class</span><span> Foo { </span></span></li>
<li>
<span class="keyword">const</span><span> ERROR_CODE = </span><span class="string">'404'</span><span>; </span>
</li>
<li class="alt">
<span class="keyword">public</span><span> </span><span class="vars">$public_ex</span><span> = </span><span class="string">'this is public'</span><span>; </span>
</li>
<li>
<span class="keyword">private</span><span> </span><span class="vars">$private_ex</span><span> = </span><span class="string">'this is private!'</span><span>; </span>
</li>
<li class="alt">
<span class="keyword">protected</span><span> </span><span class="vars">$protected_ex</span><span> = </span><span class="string">'this should be protected'</span><span>; </span>
</li>
<li>
<span class="keyword">public</span><span> </span><span class="keyword">function</span><span> getErrorCode() { </span>
</li>
<li class="alt">
<span class="keyword">return</span><span> self::ERROR_CODE; </span>
</li>
<li><span>} </span></li>
<li class="alt"><span>} </span></li>
</ol>Now, perform json conversion on the instance of this class:
<ol class="dp-c"> <li class="alt"><span><span class="vars">$foo</span><span> = </span><span class="keyword">new</span><span> Foo; </span></span></li> <li> <span class="vars">$foo_json</span><span> = json_encode(</span><span class="vars">$foo</span><span>); </span> </li> <li class="alt"> <span class="func">echo</span><span> </span><span class="vars">$foo_json</span><span>; </span> </li> </ol>
Output The result is
<ol class="dp-c"><li class="alt"><span><span>{</span><span class="string">"public_ex"</span><span>:</span><span class="string">"this is public"</span><span>} </span></span></li></ol>You can see that except for public variables (public), other things (constants, private variables, methods, etc.) are missing.
4. json_decode()
This function is used to convert json text into the corresponding PHP data structure. Here is an example:
<ol class="dp-c">
<li class="alt"><span><span class="vars">$json</span><span> = </span><span class="string">'{"foo": 12345}'</span><span>; </span></span></li>
<li>
<span class="vars">$obj</span><span> = json_decode(</span><span class="vars">$json</span><span>); </span>
</li>
<li class="alt">
<span>print </span><span class="vars">$obj</span><span>->{</span><span class="string">'foo'</span><span>}; </span><span class="comment">// 12345</span><span> </span>
</li>
</ol>Normally, json_decode() always returns a PHP object, not an array. For example:
<ol class="dp-c">
<li class="alt"><span><span class="vars">$json</span><span> = </span><span class="string">'{"a":1,"b":2,"c":3,"d":4,"e":5}'</span><span>; </span></span></li>
<li>
<span>var_dump(json_decode(</span><span class="vars">$json</span><span>)); </span>
</li>
</ol>The result is to generate a PHP object:
<ol class="dp-c">
<li class="alt"><span><span>object(stdClass)#1 (5) { </span></span></li>
<li>
<span>[</span><span class="string">"a"</span><span>] => int(1) </span>
</li>
<li class="alt">
<span>[</span><span class="string">"b"</span><span>] => int(2) </span>
</li>
<li>
<span>[</span><span class="string">"c"</span><span>] => int(3) </span>
</li>
<li class="alt">
<span>[</span><span class="string">"d"</span><span>] => int(4) </span>
</li>
<li>
<span>[</span><span class="string">"e"</span><span>] => int(5) </span>
</li>
<li class="alt"><span>} </span></li>
</ol>If you want to force the generation of a PHP associative array, json_decode() needs to add a parameter true:
<ol class="dp-c">
<li class="alt"><span><span class="vars">$json</span><span> = </span><span class="string">'{"a":1,"b":2,"c":3,"d":4,"e":5}'</span><span>; </span></span></li>
<li>
<span>var_dump(json_decode(</span><span class="vars">$json</span><span>),true); </span>
</li>
</ol>The result is an associative array:
<ol class="dp-c">
<li class="alt"><span><span class="keyword">array</span><span>(5) { </span></span></li>
<li>
<span>[</span><span class="string">"a"</span><span>] => int(1) </span>
</li>
<li class="alt">
<span>[</span><span class="string">"b"</span><span>] => int(2) </span>
</li>
<li>
<span>[</span><span class="string">"c"</span><span>] => int(3) </span>
</li>
<li class="alt">
<span>[</span><span class="string">"d"</span><span>] => int(4) </span>
</li>
<li>
<span>[</span><span class="string">"e"</span><span>] => int(5) </span>
</li>
<li class="alt"><span>} </span></li>
</ol>5. Common errors of json_decode()
The following three ways of writing json are all wrong , can you see where the error is?
<ol class="dp-c">
<li class="alt"><span><span class="vars">$bad_json</span><span> = </span><span class="string">"{ 'bar': 'baz' }"</span><span>; </span></span></li>
<li>
<span class="vars">$bad_json</span><span> = </span><span class="string">'{ bar: "baz" }'</span><span>; </span>
</li>
<li class="alt">
<span class="vars">$bad_json</span><span> = </span><span class="string">'{ "bar": "baz", }'</span><span>; </span>
</li>
</ol>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.
<ol class="dp-c"><li class="alt"><span><span>var_dump(json_decode(</span><span class="string">"Hello World"</span><span>)); </span><span class="comment">//null</span><span> </span></span></li></ol>
6. Reference Materials
* PHP Manual (http://php.net/manual/en/book.json.php)
* Ed Finkler, JSON is Everybody's Friend (http://phpadvent.org/2008/json-is-everybodys-friend-by-ed-finkler)
Original address: http://www .ruanyifeng.com/blog/2011/01/json_in_php.html
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