PHP实现过滤掉非汉字字符只保留中文字符

<div class="jb51code">
<pre class="brush:PHP;">
<?php

$str = "a 1b 2b＜中文＞。xxyy字符";

//转换 GB2312 -> UTF-8
$str = mb_convert_encoding($str,'UTF-8','GB2312');

preg_match_all('/[\x{4e00}-\x{9fff}]+/u',$str,$matches);
$str = join('',$matches[0]);

//转换 UTF-8 -> GB2312
$str = mb_convert_encoding($str,'GB2312','UTF-8');

echo $str; //输出 中文字符

?>