JSON 是一项旨在允许中间件创建使用 JavaScript 固有格式的对象的协议。它最强大的属性是它是一种轻量级协议。简单处理 RSS 聚合或 recipe 列表时，您不需要在 JavaScript 中使用 XML 的全部功能。不需要验证格式或确保严格的数据键入。
PHP JSON扩展编码和解码
有两个函数用于PHP JSON扩展：encode 和 decode。第一个函数将把任意类型的数据对象转换为一组序列化数据，以供 JavaScript 处理。第二个函数将把序列化数据解码，并将其转换为基本 PHP 对象或联合数组。我们来看一看 json_decode()。
json_decode() 的示例
<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php </span></span></span></li>
<li>
<span>$</span><span class="attribute">jsonObject</span><span> = </span><span class="attribute-value">'{"21":{"url":"www.blah.com<br>/story1.html","title":"JSON is sweeping<br> AJAX world","viewed":false},"22":{"url":<br>"www.blah.com/story2.html","title":"JSON <br>is great","viewed":false}}'</span><span>; </span>
</li>
<li class="alt">
<span>$</span><span class="attribute">decodedObject</span><span> = </span><span class="attribute-value">json_decode</span><span>($jsonObject); </span>
</li>
<li>
<span>$</span><span class="attribute">decodedArray</span><span> = </span><span class="attribute-value">json_decode</span><span>($jsonObject, true); </span>
</li>
<li class="alt"><span>print_r($decodedObject); </span></li>
<li>
<span>echo "</span><span class="tag"><span> </span><span class="tag-name">br</span><span class="tag">></span><span class="tag"><span> </span><span class="tag-name">br</span><span class="tag">></span><span>"; </span></span></span>
</li>
<li class="alt"><span>print_r($decodedArray); </span></li>
<li>
<span class="tag">?></span><span> </span>
</li>
<li class="alt"><span> </span></li>
</ol>如上，我们有一个 PHP 脚本，该脚本将获取 $jsonObject 并将其解码回 PHP 固有对象。我们进行了两次解码。第一次，使用未经修改的用法，这将得到 stdClass 的对象；第二次，使用布尔型参数来创建联合数组。
以下是decode的输出：
<ol class="dp-xml"> <li class="alt"><span><span>stdClass Object ( [21] =</span><span class="tag">></span><span> <br>stdClass Object ( [url] =</span><span class="tag">></span><span> <br>www.blah.com/story1.html [title] =</span><span class="tag">></span><span> <br>JSON is sweeping AJAX world [viewed] =</span><span class="tag">><br></span><span> ) [22] =</span><span class="tag">></span><span> stdClass Object ( [url] =</span><span class="tag">><br></span><span> www.blah.com/story2.html [title] =</span><span class="tag">></span><span> <br>JSON is great [viewed] =</span><span class="tag">></span><span> ) ) Array ( [21] =</span><span class="tag">></span><span> <br>Array ( [url] =</span><span class="tag">></span><span> www.blah.com/story1.html <br>[title] =</span><span class="tag">></span><span> JSON is sweeping AJAX world<br> [viewed] =</span><span class="tag">></span><span> ) [22] =</span><span class="tag">></span><span> Array ( [url] =</span><span class="tag">><br></span><span> www.blah.com/story2.html [title] =</span><span class="tag">><br></span><span> JSON is great [viewed] =</span><span class="tag">></span><span> ) ) </span></span></li> <li><span> </span></li> </ol>
我们再来看看encode:
<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php </span></span></span></li>
<li>
<span>$</span><span class="attribute">results</span><span> = </span><span class="attribute-value">array</span><span>("21" =</span><span class="tag">></span><span> </span>
</li>
<li class="alt">
<span>array("url" =</span><span class="tag">></span><span> </span>
</li>
<li>
<span>"www.blah.com/story1.html", "title" =</span><span class="tag">></span><span> </span>
</li>
<li class="alt">
<span>"JSON is sweeping AJAX world", "viewed" =</span><span class="tag">></span><span> </span>
</li>
<li>
<span>FALSE), "22" =</span><span class="tag">></span><span> array("url"=</span><span class="tag">></span><span> </span>
</li>
<li class="alt">
<span>"www.blah.com/story2.html", "title" =</span><span class="tag">></span><span> </span>
</li>
<li>
<span>"JSON is great", "viewed" =</span><span class="tag">></span><span> FALSE)); </span>
</li>
<li class="alt">
<span>$</span><span class="attribute">jsonObject</span><span> = </span><span class="attribute-value">json_encode</span><span>($results); </span>
</li>
<li><span>echo $jsonObject; </span></li>
<li class="alt">
<span class="tag">?></span><span> </span>
</li>
<li><span> </span></li>
</ol>没有使用递归。没有添加标记。只需将其传入 json_encode() 函数，然后它将从另一端作为 JSON 序列化对象传出。
结束语
JSON 是一种有用的、轻量级协议，现在可用于 PHP V5.2，它可以轻松地实现从 PHP 应用程序中提取出数据，并将其放入 Ajax 应用程序的过程。相应地，PHP JSON扩展同样也是轻量级且十分有用的，只包含两个易于使用的函数。
使用这些函数，我们可以转换和导出对象结构，还可以使用 json_encode() 使来自 PHP 数据库连接的数据可用于 Ajax 应用程序。在 Ajax 应用程序中处理完数据后，可以将数据返回 PHP 脚本并用 json_decode() 重新创建可用的对象数据结构。当把数据返回到 PHP 后，我们可以将其存储到数据库中，或使用 PHP 提供的众多选择中的任何其他数据处理方法。
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