抓取淘宝天猫的商品的促销价格

通过商品的url获取促销价，天猫淘宝的促销价并不是直接生成的，而是通过js间接生成的。所以通过jsoup等工具无法抓取。

首先是尝试使用htmlUnit,因为其可以，模拟浏览器运行js、css。经试验，htmlunit确实可以运行js，尝试抓取我自己的网站，可成功获取ajax、js生成的内容。但在抓取淘宝网站时出现异常，htmlunit对网站内容的格式有一定的要求，于是只能想其他办法(以后再尝试此方法)。

接着使用httpwatch分析淘宝的请求，发现其中一个请求返回的值中有促销价的信息。

这个请求有2个关键点，关键1：参数itemid（就是商品的id）。关键2：是请求header的Referer。

具体代码如下：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;


public class Test4Taobao {

	public static void main(String[] args) throws ClientProtocolException, IOException {
		HttpClient httpclient = new DefaultHttpClient();
		String url="http://detail.tmall.com/item.htm?spm=a230r.1.14.44.RoTYht&id=43508885384&ns=1&abbucket=20";
		String id=getStrByPrePost(url, "id=", "&");//根据url获取商品的id
		if(id!=null){
			//组装出获取商品信息的url
			String detailUrl="http://mdskip.taobao.com/core/initItemDetail.htm?itemId="+id+"×tamp=1429065419751&tgTag=false&cartEnable=true&addressLevel=2&progressiveSupport=false&isUseInventoryCenter=false&household=false¬AllowOriginPrice=false&isRegionLevel=false&sellerUserTag=303632416&sellerUserTag2=18020085046181888&tmallBuySupport=true&isAreaSell=false&queryMemberRight=true&isIFC=false&sellerUserTag3=70368779862144&sellerUserTag4=8800522208643&service3C=true&tryBeforeBuy=false&isSecKill=false&isForbidBuyItem=false&sellerPreview=false&itemTags=843,1163,1478,1483,1547,1611,1803,1867,2049,2059,2443,2507,2635,3787,3974,4166,4555,4811,5323,21762,21826,25282,28802,29122,34178,56130,56194&isApparel=false&offlineShop=false&showShopProm=false&callback=setMdskip";
			HttpGet get = new HttpGet(detailUrl);
			get.addHeader("Referer", url);//Referer必须要设置
			HttpResponse response = httpclient.execute(get);
			String content =  getContent(response);
			content=getStrByPrePost(content, "setMdskip(", ")");
			//返回的内容是json格式，可以通过gson等来解析，为了方便，此处直接截取。
			System.out.println("商品信息:"+content);
			String promotionPrice = getStrByPrePost(content, "promotionList", null);
			promotionPrice = getStrByPrePost(promotionPrice, "\"price\":", ",");
			System.out.println("商品价格:"+promotionPrice);
		}
		
	}
	
	/**
	 * 获取返回内容的string
	 * @param response
	 * @return
	 * @throws IllegalStateException
	 * @throws IOException
	 */
	private static String getContent(HttpResponse response) throws IllegalStateException, IOException {
		java.io.InputStream is = response.getEntity().getContent();
		BufferedReader br = new BufferedReader(new InputStreamReader(is, "GBK"));//response.getEntity().getContentEncoding().getName()
		String line = "";
		String temp= null;
		while ((temp = br.readLine()) != null) {
			line+=temp;
		}
		return line;
		
	}

	/**
	 * 根据前后的文本截取指定的内容。
	 * @param str
	 * @param pre
	 * @param post
	 * @return
	 */
	public static String getStrByPrePost(String str,String pre,String post){
		if(str!=null){
			if(pre!=null){
				int s = str.indexOf(pre);
				if(s>-1){
					str = str.substring(s+pre.length(), str.length());
				}else{
					return null;
				}
				
			}
			if(post!=null){
				int e =  str.indexOf(post);
				if(e>-1){
					str = str.substring(0,e);
				}else{
					return null;
				}
				
			}
		}
		
		return str;
	}
}

to be continued