摘要：支持基于段方法和查詢字符串方法兩種形式的。里的方法就是利用類來實現解析出類名方法名。在類的構造函數里有一步方法代碼如下如果你的原始是的話，經過這個方法處理，你會得到參考文章

路由的目的是為了從URL中解析出class類名是什么，method方法名是什么，所傳的參數有哪些，參數值又是什么，類文件存在的路徑是哪。最終實現方法的調度。

CI支持基于段方法和查詢字符串方法兩種形式的URL。

基于段形式：

example.com/news/article/my_article.html

查詢字符串形式：

index.php?c=products&m=view&id=345

URL的獲取方法有如下幾種：PATH_INFO、QUERY_STRING、REQUEST_URI、ORIG_PATH_INFO。比較常用的是PATH_INFO。幾種方式的差異可以簡單通過打印$_SERVER來查看。比如xxx.com/welcome/test_search.html?c=welcome&d=test_search，打印的結果是（只挑了這幾部分）：

Array
(
    [QUERY_STRING] => c=welcome&d=test_search
    [REQUEST_URI] => /welcome/test_search.html?c=welcome&d=test_search
    [PATH_INFO] => /welcome/test_search.html
)

下面是源碼config文件里關于這幾種方法的定義。

/*
|--------------------------------------------------------------------------
| URI PROTOCOL
|--------------------------------------------------------------------------
|
| This item determines which server global should be used to retrieve the
| URI string.  The default setting of "AUTO" works for most servers.
| If your links do not seem to work, try one of the other delicious flavors:
|
| "AUTO"            Default - auto detects
| "PATH_INFO"       Uses the PATH_INFO
| "QUERY_STRING"    Uses the QUERY_STRING
| "REQUEST_URI"     Uses the REQUEST_URI
| "ORIG_PATH_INFO"  Uses the ORIG_PATH_INFO
|
*/
$config["uri_protocol"] = "PATH_INFO";

我們這里用的也是PATH_INFO來獲取。

至此，我們就擁有了URL地址，接下來我們就要分析地址。URL類就是來做分析的事情。

system/core/Router.php里的_set_routing()方法就是利用URL類來實現解析出類名方法名。

看下代碼（下面的代碼都是CodeIgniter-3.0.6版本的），英文注釋已經很詳細了，我在關鍵點額外加了點中文注釋：

/**
 * Set route mapping
 *
 * Determines what should be served based on the URI request,
 * as well as any "routes" that have been set in the routing config file.
 *
 * @return    void
 */
protected function _set_routing()
{
    // Load the routes.php file. It would be great if we could
    // skip this for enable_query_strings = TRUE, but then
    // default_controller would be empty ...
    if (file_exists(APPPATH."config/routes.php"))
    {
        include(APPPATH."config/routes.php");
    }

    if (file_exists(APPPATH."config/".ENVIRONMENT."/routes.php"))
    {
        include(APPPATH."config/".ENVIRONMENT."/routes.php");
    }

    // Validate & get reserved routes
    if (isset($route) && is_array($route))
    {
        isset($route["default_controller"]) && $this->default_controller = $route["default_controller"];
        isset($route["translate_uri_dashes"]) && $this->translate_uri_dashes = $route["translate_uri_dashes"];
        unset($route["default_controller"], $route["translate_uri_dashes"]);
        $this->routes = $route;
    }

    // Are query strings enabled in the config file? Normally CI doesn"t utilize query strings
    // since URI segments are more search-engine friendly, but they can optionally be used.
    // If this feature is enabled, we will gather the directory/class/method a little differently
    // 這段不用看，我們項目中是FALSE
    if ($this->enable_query_strings)
    {
        // If the directory is set at this time, it means an override exists, so skip the checks
        if ( ! isset($this->directory))
        {
            $_d = $this->config->item("directory_trigger");
            $_d = isset($_GET[$_d]) ? trim($_GET[$_d], "