Scrapy 爬取动态页面

　　目前绝大多数的网站的页面都是冬天页面，动态页面中的部分内容是浏览器运行页面中的JavaScript 脚本动态生成的，爬取相对比较困难

先来看一个很简单的动态页面的例子，在浏览器中打开 http://quotes.toscrape.com/js，显示如下：

页面总有十条名人名言，每一条都包含在<div class = "quote">元素中，现在我们在 Scrapy shell中尝试爬取页面中的名人名言：

$ scrapy shell http://quotes.toscrape.com/js/
...
>>> response.css(''div.quote)
[]

从结果可以看出，爬取失败了，在页面中没有找到任何包含名人名言的 <div class = 'quote'>元素。这些 <div class = 'qoute'>就是动态内容，从服务器下载的页面中并不包含他们（多以我们爬去失败），浏览器执行了页面中的一段 JavaScript 代码后，他们才被生成出来。

　　

图中的 JavaScript 代码如下：

　　

 var data = [
    {
        "tags": [
            "change",
            "deep-thoughts",
            "thinking",
            "world"
        ],
        "author": {
            "name": "Albert Einstein",
            "goodreads_link": "/author/show/9810.Albert_Einstein",
            "slug": "Albert-Einstein"
        },
        "text": "\u201cThe world as we have created it is a process of our thinking. It cannot be changed without changing our thinking.\u201d"
    },
    {
        "tags": [
            "abilities",
            "choices"
        ],
        "author": {
            "name": "J.K. Rowling",
            "goodreads_link": "/author/show/1077326.J_K_Rowling",
            "slug": "J-K-Rowling"
        },
        "text": "\u201cIt is our choices, Harry, that show what we truly are, far more than our abilities.\u201d"
    },
    {
        "tags": [
            "inspirational",
            "life",
            "live",
            "miracle",
            "miracles"
        ],
        "author": {
            "name": "Albert Einstein",
            "goodreads_link": "/author/show/9810.Albert_Einstein",
            "slug": "Albert-Einstein"
        },
        "text": "\u201cThere are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.\u201d"
    },
    {
        "tags": [
            "aliteracy",
            "books",
            "classic",
            "humor"
        ],
        "author": {
            "name": "Jane Austen",
            "goodreads_link": "/author/show/1265.Jane_Austen",
            "slug": "Jane-Austen"
        },
        "text": "\u201cThe person, be it gentleman or lady, who has not pleasure in a good novel, must be intolerably stupid.\u201d"
    },
    {
        "tags": [
            "be-yourself",
            "inspirational"
        ],
        "author": {
            "name": "Marilyn Monroe",
            "goodreads_link": "/author/show/82952.Marilyn_Monroe",
            "slug": "Marilyn-Monroe"
        },
        "text": "\u201cImperfection is beauty, madness is genius and it's better to be absolutely ridiculous than absolutely boring.\u201d"
    },
    {
        "tags": [
            "adulthood",
            "success",
            "value"
        ],
        "author": {
            "name": "Albert Einstein",
            "goodreads_link": "/author/show/9810.Albert_Einstein",
            "slug": "Albert-Einstein"
        },
        "text": "\u201cTry not to become a man of success. Rather become a man of value.\u201d"
    },
    {
        "tags": [
            "life",
            "love"
        ],
        "author": {
            "name": "Andr\u00e9 Gide",
            "goodreads_link": "/author/show/7617.Andr_Gide",
            "slug": "Andre-Gide"
        },
        "text": "\u201cIt is better to be hated for what you are than to be loved for what you are not.\u201d"
    },
    {
        "tags": [
            "edison",
            "failure",
            "inspirational",
            "paraphrased"
        ],
        "author": {
            "name": "Thomas A. Edison",
            "goodreads_link": "/author/show/3091287.Thomas_A_Edison",
            "slug": "Thomas-A-Edison"
        },
        "text": "\u201cI have not failed. I've just found 10,000 ways that won't work.\u201d"
    },
    {
        "tags": [
            "misattributed-eleanor-roosevelt"
        ],
        "author": {
            "name": "Eleanor Roosevelt",
            "goodreads_link": "/author/show/44566.Eleanor_Roosevelt",
            "slug": "Eleanor-Roosevelt"
        },
        "text": "\u201cA woman is like a tea bag; you never know how strong it is until it's in hot water.\u201d"
    },
    {
        "tags": [
            "humor",
            "obvious",
            "simile"
        ],
        "author": {
            "name": "Steve Martin",
            "goodreads_link": "/author/show/7103.Steve_Martin",
            "slug": "Steve-Martin"
        },
        "text": "\u201cA day without sunshine is like, you know, night.\u201d"
    }
];
    for (var i in data) {
        var d = data[i];
        var tags = $.map(d['tags'], function(t) {
            return "<a class='tag'>" + t + "</a>";
        }).join(" ");
        document.write("<div class='quote'><span class='text'>" + d['text'] + "</span><span>by <small class='author'>" + d['author']['name'] + "</small></span><div class='tags'>Tags: " + tags + "</div></div>");
        }

　　阅读代码可以了解页面中动态生成的细节，所有名人名言信息被保存在数组 data 中，最后的 for 循环迭代 data 中的每项信息，使用 document。write 生成每条名人名言对应的 <div class = ‘quote’>元素。

　　上面是动态页面中最简单的一个例子，数据被应编码到 JavaScript 代码中， 实际中更常见的是JavaScript 通过 HTTP 请求跟网站动态交互获取数据（AJAX），然后使用数据更新 HTMML 页面。爬取此类动态网页需要先执行页面使用 JavaScript 渲染引擎页面，咋进行爬取。