simple-scrapy

#详解Node.js API系列 Http模块(2) CNodejs爬虫实现

##简单爬虫设计

var http = require('http');
http.get("http://cnodejs.org/", function(res) {
	var size = 0;
	var chunks = [];
  res.on('data', function(chunk){
  	size += chunk.length;
  	chunks.push(chunk);
  });
  res.on('end', function(){
  	var data = Buffer.concat(chunks, size);
  	console.log(data.toString())
  });
}).on('error', function(e) {
  console.log("Got error: " + e.message);
});

###http.get(options, callback)

http://cnodejs.org/ 爬行目标地址。
res.on('data') 监听data事件。
res.on('end') 数据获取完毕事件。
Buffer.concat(chunks, size); 连接多次data的buff。
data.toString() 将data二进制数据转换成utf-8的字符串，如果页面是GBK的时候，请使用iconv模块进行转换，原生Node.js不支持GBK。

##设计目标

制定爬虫的url规则
分析页面信息
清洗没用数据
存储有用数据

##制定爬虫的url规则

观察 http://cnodejs.org/ 的url规则，http://cnodejs.org/?page=页数，根据规则，不难想出处理的思路，首先获取用迭代器模式是最方便的，首先，获取单个page页里面的单个page路径，通过路径爬取page的页面内容。采用迭代器模式是最方便的，next()做page的页面索引，hasNext()判断page页是否超出了有效范围,超出范围则停止索引，下面是伪代码

var Urls = function(start_url){
  this.start_url = start_url; //base url
  this.page = 0;  //url page
  this.targetPage = ''; //topic page
}
Urls.prototype.next = function(){
  var data;
  if (!this.hasNext()) {
      return null;
  }
  this.page += 1;
  data = request.get(this.targetPage)  //get topic page
  return data;
}
Urls.prototype.hasNext = function(){
  //http://cnodejs.org/p=[1,2,3,4]
  var url = this.start_url + this.page;
  // if get page success from url,return ture,or return false
  // get topic page url
}
// main     
var urls = new Urls();
while(urls.hasNext()){
  console.log(urls.next());
}

##分析页面数据

分析页面的过程，主要工作是分析页面的元素提取出目标的内容，例如正文和评论等。这里我们需要采用cheerio的第三方库,该模块采取类似Jquery方式的DOM选择器，通过DOM选择器来实现信息提取。

npm install cheerio

项目地址：https://github.com/MatthewMueller/cheerio

官方demo例子

var cheerio = require('cheerio'),
    $ = cheerio.load('<h2 class="title">Hello world</h2>');

$('h2.title').text('Hello there!');
$('h2').addClass('welcome');

$.html();
//=> <h2 class="title welcome">Hello there!</h2>

提取cnodejs的topics 链接

$ = cheerio.load(data); //data是的页面数据
topics = $('.cell .topic_wrap a')
for(var i=0; i < topics.length; i++){
console.log(topics[i].attribs['href'])

result：

/topic/52386d26101e574521a12ccd
/topic/5232cd39101e57452106ce5a
/topic/52390cdb101e574521b1e252
/topic/521b1dcabee8d3cb128c56dd
/topic/5238c6d2101e574521aaca13
/topic/52380b4e101e57452193617c

内容信息提取

提取condejs帖子内容和标题

$ = cheerio.load(data);  
var topic = $('.inner.topic');  
console.log(topic.children('h3').text()) //标题
var content = topic.children('.topic_content').text()
console.log(content);   //文章内容

##清洗没用的数据

由于爬取的内容，可能带有html标签或者表情方面的信息，可能跟目标内容不符合，通过这个环节来过滤，这里向大家推荐一个模块 validator,该模块可以过滤xss攻击，字符串里面的空格，判断内容的属性等，详细可以到项目地址学习 https://github.com/chriso/node-validator

安装

npm install validator

demo例子

var check = require('validator').check,
    sanitize = require('validator').sanitize
//Validate
check('test@email.com').len(6, 64).isEmail();        //Methods are chainable
check('abc').isInt();                                //Throws 'Invalid integer'
check('abc', 'Please enter a number').isInt();       //Throws 'Please enter a number'
check('abcdefghijklmnopzrtsuvqxyz').is(/^[a-z]+$/);
//Set a message per validator
check('foo', {
    isNumeric: 'This is not a number',
    contains: 'The value doesn\'t have a 0 in it'
}).isNumeric().contains('0');
//Referencing validator args from the message
check('foo', 'The message needs to be between %1 and %2 characters long (you passed "%0")').len(2, 6);
//Sanitize / Filter
var int = sanitize('0123').toInt();                  //123
var bool = sanitize('true').toBoolean();             //true
var str = sanitize(' \t\r hello \n').trim();         //'hello'
var str = sanitize('aaaaaaaaab').ltrim('a');         //'b'
var str = sanitize(large_input_str).xss();
var str = sanitize('&lt;a&gt;').entityDecode();      //'<a>'

过滤刚才爬取的内容，主要是过滤空格

var topic = $('.inner.topic');  
title = topic.children('h3').text() //标题
sanitize(title).trim()

##存储有用数据

咸鱼白菜各有所需，对于游泳的数据，可以存成文本，也可以存到数据库，本次实例，为了足够精简，所以不采用数据库存储，采用文本的方式记录和json的格式记录数据。

一个爬虫的流程完成了，我们来重新看看实现代码

vi url.js

var http = require('http');
var cheerio = require('cheerio');
var sanitize = require('validator').sanitize;
var async = require('async');
var fs = require('fs');

var BASE_URL = 'http://cnodejs.org'
var scrapy = {}
/**
 * Get page from url.
 *
 * Examples:
 *
 *     scrapy.get('http://www.baidu.com', cb);
 *     // => 'baidu page html
 * 
 * @interface
 * @param {String} url:ex http://www.baidu.com
 * @param {Function} cb
 * @private
 */
scrapy.get = function(url, cb){
  http.get(url, function(res) {

    var size = 0;
    var chunks = [];

    res.on('data', function(chunk){
      size += chunk.length;
      chunks.push(chunk);
    });

    res.on('end', function(){
      var data = Buffer.concat(chunks, size);
      cb(null, data);
    });

  }).on('error', function(e) {
    cb(e, null);
  });
}

var Urls = function(startUrl){
  this.startUrl = startUrl;
  this.page = 0;
  this.homePage = '';
}

Urls.prototype.next = function(cb){
  var self = this;

  this.hasNext(function(err, bRet){
    if(!bRet){
      return null;
    }

    self.homeParse(function(err, topics){
      self.page += 1;
      cb(null, topics);
    })
  })
}

Urls.prototype.hasNext = function(cb){
  var self = this;
  var url = this.startUrl + this.page;

  scrapy.get(url, function(err, data){
    var html = data.toString();
    $ = cheerio.load(html);
    self.homePage = $('.cell .topic_wrap a');

    if(self.homePage.length === 0){
      return cb(null, false);
    }
    return cb(null, true);

  });
};

Urls.prototype.homeParse = function(cb){
  var self = this;
  var topics = [];

  async.filter(self.homePage, function(i, cb){
    var url = BASE_URL + self.homePage[i].attribs['href']
    scrapy.get(url, function(err, topic){
      topics.push(topic.toString());
      cb(null);
    })
    
  },function(err){
    cb(err, topics);
  });
}

Urls.prototype.parseTopic = function(html){
  $ = cheerio.load(html);
  var topic = $('.inner.topic');
  var item = {};
  item.title = sanitize(topic.children('h3').text()).trim();
  item.content = sanitize(topic.children('.topic_content').text()).trim();

  return item;
};

Urls.prototype.Pipeline = function(items){

  var result = JSON.stringify(items);
  fs.writeFileSync('result.txt', result)

}

exports = module.exports = Urls

vi app.js

var Urls = require('./lib/url.js');
var async = require('async');


var startUrl = 'http://cnodejs.org/?page='

var urls = new Urls(startUrl);

urls.next(function(err, topics){
  var self = this;
  var items = [];
  async.filter(topics, function(topic, cb){
    items.push(urls.parseTopic(topic));
    cb(null);
  },function(err){
    urls.Pipeline(items);
  })
})

完整项目地址：https://github.com/youyudehexie/simple-scrapy

Name		Name	Last commit message	Last commit date
Latest commit History 4 Commits
lib		lib
node_modules		node_modules
README.md		README.md
app.js		app.js

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