<h1 class="post-title entry-title">Java分布式爬虫Nutch教程——导入Nutch工程，执行完整爬取</h1>
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<p>在使用本教程之前，需要满足条件：</p>
- 1）有一台Linux或Linux虚拟机
- 2）安装JDK（推荐1.7）
- 3）安装Apache Ant
下载Nutch源码：
推荐使用Nutch 1.9,官方下载地址：http://mirrors.hust.edu.cn/apache/nutch/1.9/apache-nutch-1.9-src.zip
安装IDE：
推荐使用Intellij或者Netbeans，如果用eclipse也可以，不推荐。
Intellij官方下载地址：http://www.jetbrains.com/idea/download/
转换：
Nutch源码是用ant进行构建的，需要转换成eclipse工程才可以导入IDE正确使用,Intellij和Netbeans都可以支持ecilpse工程。
解压下载的apache-nutch-1.9-src.zip，得到文件夹apache-nutch-1.9。
在执行转换之前，我们先修改一下ivy中的一个源，将它改为开源中国的镜像，否则转换的过程会非常缓慢。(ant源码中并没有附带依赖jar包，ivy负责从网上自动下载jar包）。
修改apache-nutch-1.9文件夹中的ivy/ivysettings.xml：
找到：
<property name="repo.maven.org"
value="http://repo1.maven.org/maven2/"
override="false"/> 
将value修改为http://maven.oschina.net/content/groups/public/ ,修改后：
<property name="repo.maven.org"
value="http://maven.oschina.net/content/groups/public/"
override="false"/> 
保存并退出，保证当前目录为apache-nutch-1.9，执行命令：
ant eclipse -verbose 然后耐心等待，这个过程ant会根据ivy从中心仓库下载各种依赖jar包，可能要十几分钟。
-verbose参数加上之后可以看到ant过程的详细信息。
10分钟左右，转换成功：
打开Intellij, File -> Import Project ->选择apache-nutch-1.9文件夹，确定后选择Import project from external model(Eclipse)
一直点击next到结束。成功将项目导入Intellij:
源码导入工程后，并不能执行完整的爬取。Nutch将爬取的流程切分成很多阶段，每个阶段分别封装在一个类的main函数中。在外面通过Linux Shell调用这些main函数，来完整爬取的流程。我们在后续教程中会对流程调度做一个详细的说明。
下面我们来运行Nutch中最简单的流程：Inject。我们知道爬虫在初始阶段，是需要人工给出一个或多个url，作为起始点（广度遍历树的树根）。Inject的作用，就是把用户写在文件里的种子(一行一个url，是TextInputFormat)，插入到爬虫的URL管理文件(crawldb，是SequenceFile)中。
从src文件夹中找到org.apache.nutch.crawl.Injector类：
在阅读Nutch源码的过程中，最重要的就是找到每个类的main函数：
可以看到,main函数其实是利用ToolRunner，执行了run(String[] args)。这里ToolRunner.run会从第二个参数(new Injector())这个对象中，找到run(String[] args)这个方法执行。
从run方法中可以看出来，String[] args需要有2个参数，第一个参数表示爬虫的URL管理文件夹(输出），第二个参数表示种子文件夹（输入）。对hadoop中的map reduce程序来说，输入文件夹是必须存在的，输出文件夹应该不存在。我们创建一个文件夹 /tmp/urls，来存放种子文件（作为输入）。
在seed.txt中加入一个种子URL
http://www.cnbeta.com/ 指定一个文件夹/tmp/crawldb来作为URL管理文件夹（输出）
有一种简单的方法来指定args，直接在main函数下加一行：
args=new String[]{"/tmp/crawldb","/tmp/urls"}; 运行这个类，我们会发现报错了（下面只给了错误的一部分）：
Caused by: java.lang.RuntimeException: x point org.apache.nutch.net.URLNormalizer not found.
at org.apache.nutch.net.URLNormalizers.<init>(URLNormalizers.java:123)
at org.apache.nutch.crawl.Injector$InjectMapper.configure(Injector.java:84)
... 23 more 这是因为用这种方式执行，按照Nutch默认的配置，不能正确地加载插件。我们需要修改Nutch的配置文件，为插件文件夹指定一个绝对路径，修改conf/nutch-default.xml文件，找到：
<property>
<name>plugin.folders</name>
<value>plugins</value>
<description>Directories where nutch plugins are located. Each
element may be a relative or absolute path. If absolute, it is used
as is. If relative, it is searched for on the classpath.</description>
</property> 将value修改为绝对路径 apache-nutch-1.9所在文件夹+”/src/plugin”，比如我的配置：
<property>
<name>plugin.folders</name>
<value>/home/hu/apache/apache-nutch-1.9/src/plugin</value>
<description>Directories where nutch plugins are located. Each
element may be a relative or absolute path. If absolute, it is used
as is. If relative, it is searched for on the classpath.</description>
</property> 建议在修改nutch-default.xml时，将原来的配置注释，并复制一份新的修改，方便还原：
现在再运行Injector.java,看到结果：
运行成功。
读取爬虫文件：
我们查看程序的输出 tree /tmp/crawldb ,如果没有tree命令，就直接用资源管理器之类的查看吧：
查看里面的data文件：
vim /tmp/crawldb/current/part-00000/data 
这是一个SequenceFile，Nutch中除了Inject的输入（种子）之外，其他文件 全部以SequenceFile的形式存储。SequenceFile的结构如下：
key0 value0
key1 value1
key2 value2
......
keyn valuen 以key value的形式，将对象序列（key value序列）存储到文件中。我们从SequenceFile头部可以看出来key value的类型。
上面的SequenceFile中，可以看出来，key的类型是org.apache.hadoop.io.Text，value的类型是org.apache.nutch.crawl.CrawlDatum。
下面教程给出如何读取SequenceFile的代码。
新建一个类org.apache.nutch.example.InjectorReader
package org.apache.nutch.example;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.nutch.crawl.CrawlDatum;
import java.io.IOException;
/**
- Created by hu on 15-2-9.
*/
public class InjectorReader {
public static void main(String[] args) throws IOException {
Configuration conf=new Configuration();
Path dataPath=new Path("/tmp/crawldb/current/part-00000/data");
FileSystem fs=dataPath.getFileSystem(conf);
SequenceFile.Reader reader=new SequenceFile.Reader(fs,dataPath,conf);
Text key=new Text();
CrawlDatum value=new CrawlDatum();
while(reader.next(key,value)){
System.out.println("key:"+key);
System.out.println("value:"+value);
}
reader.close();
}
} 运行结果：
key:http://www.cnbeta.com/
value:Version: 7
Status: 1 (db_unfetched)
Fetch time: Mon Feb 09 13:20:36 CST 2015
Modified time: Thu Jan 01 08:00:00 CST 1970
Retries since fetch: 0
Retry interval: 2592000 seconds (30 days)
Score: 1.0
Signature: null
Metadata:
_maxdepth_=1000
_depth_=1 我们可以看到，程序读出了刚才Inject到crawldb的url，key是url，value是一个CrawlDatum对象，这个对象用来维护爬虫的URL管理信息，我们可以看到一行：
Status: 1 (db_unfetched) 表示当前url为未爬取状态，在后续流程中，爬虫会从crawldb取未爬取的url进行爬取。
完整爬取：
下面给出的是各位最期待的代码，就是如何用Nutch完成一次完整的爬取。官方代码在1.7之前（包括1.7），包含一个Crawl.java，这个代码的main函数可以执行一次完整的爬取，但是从1.7之后就取消了。只保留了使用Linux Shell来调用每个流程，来完成爬取的方法。但是好在取消的Crawl.java修改一下，还是可以使用的。
在爬取之前，我们先修改一下conf/nutch-default.xml中的一个地方，找到：
<property>
<name>http.agent.name</name>
<value></value>
<description>HTTP 'User-Agent' request header. MUST NOT be empty -
please set this to a single word uniquely related to your organization.
NOTE: You should also check other related properties:
http.robots.agents
http.agent.description
http.agent.url
http.agent.email
http.agent.version
and set their values appropriately.
</description>
</property> 在
<property>
<name>http.agent.name</name>
<value>test</value>
<description>HTTP 'User-Agent' request header. MUST NOT be empty -
please set this to a single word uniquely related to your organization.
NOTE: You should also check other related properties:
http.robots.agents
http.agent.description
http.agent.url
http.agent.email
http.agent.version
and set their values appropriately.
</description>
</property> 这个值会在发送http请求时，作为User-Agent字段。
下面给出代码：
package org.apache.nutch.crawl;
import java.util.;
import java.text.;
// Commons Logging imports
import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hadoop.fs.;
import org.apache.hadoop.conf.;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
import org.apache.nutch.parse.ParseSegment;
import org.apache.nutch.indexer.IndexingJob;
//import org.apache.nutch.indexer.solr.SolrDeleteDuplicates;
import org.apache.nutch.util.HadoopFSUtil;
import org.apache.nutch.util.NutchConfiguration;
import org.apache.nutch.util.NutchJob;
import org.apache.nutch.fetcher.Fetcher;
public class Crawl extends Configured implements Tool {
public static final Logger LOG = LoggerFactory.getLogger(Crawl.class);
</span></span><span class="kwd"><span class="kwd">private</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">static</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">String</span></span><span class="pln"><span class="pln"> getDate</span></span><span class="pun"><span class="pun">()</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">return</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">SimpleDateFormat</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"yyyyMMddHHmmss"</span></span><span class="pun"><span class="pun">).</span></span><span class="pln"><span class="pln">format
</span></span><span class="pun"><span class="pun">(</span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Date</span></span><span class="pun"><span class="pun">(</span></span><span class="typ"><span class="typ">System</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">currentTimeMillis</span></span><span class="pun"><span class="pun">()));</span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
</span></span><span class="com"><span class="com">/* Perform complete crawling and indexing (to Solr) given a set of root urls and the -solr
parameter respectively. More information and Usage parameters can be found below. */</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">public</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">static</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">void</span></span><span class="pln"><span class="pln"> main</span></span><span class="pun"><span class="pun">(</span></span><span class="typ"><span class="typ">String</span></span><span class="pln"><span class="pln"> args</span></span><span class="pun"><span class="pun">[])</span></span><span class="pln"><span class="pln"> throws </span></span><span class="typ"><span class="typ">Exception</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Configuration</span></span><span class="pln"><span class="pln"> conf </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">NutchConfiguration</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">create</span></span><span class="pun"><span class="pun">();</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">int</span></span><span class="pln"><span class="pln"> res </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">ToolRunner</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">run</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">conf</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Crawl</span></span><span class="pun"><span class="pun">(),</span></span><span class="pln"><span class="pln"> args</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">System</span></span><span class="pun"><span class="pun">.</span></span><span class="kwd"><span class="kwd">exit</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">res</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
</span></span><span class="lit"><span class="lit">@Override</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">public</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">int</span></span><span class="pln"><span class="pln"> run</span></span><span class="pun"><span class="pun">(</span></span><span class="typ"><span class="typ">String</span></span><span class="pun"><span class="pun">[]</span></span><span class="pln"><span class="pln"> args</span></span><span class="pun"><span class="pun">)</span></span><span class="pln"><span class="pln"> throws </span></span><span class="typ"><span class="typ">Exception</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln">
</span></span><span class="com"><span class="com">/*种子所在文件夹*/</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> rootUrlDir </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"/tmp/urls"</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="com"><span class="com">/*存储爬取信息的文件夹*/</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> dir </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"/tmp"</span></span><span class="pun"><span class="pun">,</span></span><span class="str"><span class="str">"crawl-"</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> getDate</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">int</span></span><span class="pln"><span class="pln"> threads </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="lit"><span class="lit">50</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln">
</span></span><span class="com"><span class="com">/*广度遍历时爬取的深度，即广度遍历树的层数*/</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">int</span></span><span class="pln"><span class="pln"> depth </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="lit"><span class="lit">2</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">long</span></span><span class="pln"><span class="pln"> topN </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="lit"><span class="lit">10</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">JobConf</span></span><span class="pln"><span class="pln"> job </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">NutchJob</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">FileSystem</span></span><span class="pln"><span class="pln"> fs </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">FileSystem</span></span><span class="pun"><span class="pun">.</span></span><span class="kwd"><span class="kwd">get</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">job</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">if</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">isInfoEnabled</span></span><span class="pun"><span class="pun">())</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln">
LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"crawl started in: "</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> dir</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"rootUrlDir = "</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> rootUrlDir</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"threads = "</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> threads</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"depth = "</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> depth</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">if</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">topN </span></span><span class="pun"><span class="pun">!=</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Long</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">MAX_VALUE</span></span><span class="pun"><span class="pun">)</span></span><span class="pln"><span class="pln">
LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"topN = "</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> topN</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> crawlDb </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">dir </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> </span></span><span class="str"><span class="str">"/crawldb"</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> linkDb </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">dir </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> </span></span><span class="str"><span class="str">"/linkdb"</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> segments </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">dir </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> </span></span><span class="str"><span class="str">"/segments"</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> indexes </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">dir </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> </span></span><span class="str"><span class="str">"/indexes"</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> index </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">dir </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> </span></span><span class="str"><span class="str">"/index"</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pln"><span class="pln"> tmpDir </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> job</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">getLocalPath</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"crawl"</span></span><span class="pun"><span class="pun">+</span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">SEPARATOR</span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln">getDate</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Injector</span></span><span class="pln"><span class="pln"> injector </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Injector</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Generator</span></span><span class="pln"><span class="pln"> generator </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Generator</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Fetcher</span></span><span class="pln"><span class="pln"> fetcher </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">Fetcher</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">ParseSegment</span></span><span class="pln"><span class="pln"> parseSegment </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">ParseSegment</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">CrawlDb</span></span><span class="pln"><span class="pln"> crawlDbTool </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">CrawlDb</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">LinkDb</span></span><span class="pln"><span class="pln"> linkDbTool </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">new</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">LinkDb</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">getConf</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="com"><span class="com">// initialize crawlDb </span></span><span class="pln"><span class="pln">
injector</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">inject</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">crawlDb</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> rootUrlDir</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">int</span></span><span class="pln"><span class="pln"> i</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">for</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">i </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> </span></span><span class="lit"><span class="lit">0</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln"> i </span></span><span class="pun"><span class="pun"><</span></span><span class="pln"><span class="pln"> depth</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln"> i</span></span><span class="pun"><span class="pun">++)</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln"> </span></span><span class="com"><span class="com">// generate new segment </span></span><span class="pln"><span class="pln">
</span></span><span class="typ"><span class="typ">Path</span></span><span class="pun"><span class="pun">[]</span></span><span class="pln"><span class="pln"> segs </span></span><span class="pun"><span class="pun">=</span></span><span class="pln"><span class="pln"> generator</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">generate</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">crawlDb</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> segments</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">-</span></span><span class="lit"><span class="lit">1</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> topN</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> </span></span><span class="typ"><span class="typ">System</span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">currentTimeMillis</span></span><span class="pun"><span class="pun">());</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">if</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">segs </span></span><span class="pun"><span class="pun">==</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">null</span></span><span class="pun"><span class="pun">)</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln">
LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"Stopping at depth="</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> i </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> </span></span><span class="str"><span class="str">" - no more URLs to fetch."</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">break</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
fetcher</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">fetch</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">segs</span></span><span class="pun"><span class="pun">[</span></span><span class="lit"><span class="lit">0</span></span><span class="pun"><span class="pun">],</span></span><span class="pln"><span class="pln"> threads</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln"> </span></span><span class="com"><span class="com">// fetch it </span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">if</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">(!</span></span><span class="typ"><span class="typ">Fetcher</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">isParsing</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">job</span></span><span class="pun"><span class="pun">))</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln">
parseSegment</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">parse</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">segs</span></span><span class="pun"><span class="pun">[</span></span><span class="lit"><span class="lit">0</span></span><span class="pun"><span class="pun">]);</span></span><span class="pln"><span class="pln"> </span></span><span class="com"><span class="com">// parse it, if needed </span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
crawlDbTool</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">update</span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">crawlDb</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> segs</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">true</span></span><span class="pun"><span class="pun">,</span></span><span class="pln"><span class="pln"> </span></span><span class="kwd"><span class="kwd">true</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln"> </span></span><span class="com"><span class="com">// update crawldb </span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
</span></span><span class="com"><span class="com">/*
if (i > 0) {
linkDbTool.invert(linkDb, segments, true, true, false); // invert links
if (solrUrl != null) {
// index, dedup & merge
FileStatus[] fstats = fs.listStatus(segments, HadoopFSUtil.getPassDirectoriesFilter(fs));
IndexingJob indexer = new IndexingJob(getConf());
indexer.index(crawlDb, linkDb,
Arrays.asList(HadoopFSUtil.getPaths(fstats)));
SolrDeleteDuplicates dedup = new SolrDeleteDuplicates();
dedup.setConf(getConf());
dedup.dedup(solrUrl);
}
} else {
LOG.warn("No URLs to fetch - check your seed list and URL filters.");
}
*/</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">if</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">(</span></span><span class="pln"><span class="pln">LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">isInfoEnabled</span></span><span class="pun"><span class="pun">())</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">{</span></span><span class="pln"><span class="pln"> LOG</span></span><span class="pun"><span class="pun">.</span></span><span class="pln"><span class="pln">info</span></span><span class="pun"><span class="pun">(</span></span><span class="str"><span class="str">"crawl finished: "</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">+</span></span><span class="pln"><span class="pln"> dir</span></span><span class="pun"><span class="pun">);</span></span><span class="pln"><span class="pln"> </span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
</span></span><span class="kwd"><span class="kwd">return</span></span><span class="pln"><span class="pln"> </span></span><span class="lit"><span class="lit">0</span></span><span class="pun"><span class="pun">;</span></span><span class="pln"><span class="pln">
</span></span><span class="pun"><span class="pun">}</span></span><span class="pln"><span class="pln">
} 运行成功，对网站进行了一个2层的爬取，爬取信息都保存在/tmp/crawl+时间的文件夹中。
2015-02-09 14:23:17,171 INFO crawl.CrawlDb (CrawlDb.java:update(115)) - CrawlDb update: finished at 2015-02-09 14:23:17, elapsed: 00:00:01
2015-02-09 14:23:17,171 INFO crawl.Crawl (Crawl.java:run(117)) - crawl finished: /tmp/crawl-20150209142212 有些时候爬虫爬一层就停止了，有几种原因：
- 1）种子对应的页面大小超过配置的上限，页面被忽略。
- 2）nutch默认遵循robots协议，有可能robots协议禁止了爬取，不过出现这种情况日志会给出相关信息。
- 3）网页没有被正确爬取（这种情况少）。
爬很多门户网站时容易出现第一种情况，这种情况只需要找到conf/nutch-default.xml中的：
<property>
<name>http.content.limit</name>
<value>65536</value>
<description>The length limit for downloaded content using the http://
protocol, in bytes. If this value is nonnegative (>=0), content longer
than it will be truncated; otherwise, no truncation at all. Do not
confuse this setting with the file.content.limit setting.
</description>
</property> 将value设置为-1即可
<property>
<name>http.content.limit</name>
<value>-1</value>
<description>The length limit for downloaded content using the http://
protocol, in bytes. If this value is nonnegative (>=0), content longer
than it will be truncated; otherwise, no truncation at all. Do not
confuse this setting with the file.content.limit setting.
</description>
</property> 如果看到日志中有说被robots协议阻拦，修改Fetcher.java的源码，找到：
if (!rules.isAllowed(fit.u.toString())) {
// unblock
fetchQueues.finishFetchItem(fit, true);
if (LOG.isDebugEnabled()) {
LOG.debug("Denied by robots.txt: " + fit.url);
}
output(fit.url, fit.datum, null, ProtocolStatus.STATUS_ROBOTS_DENIED, CrawlDatum.STATUS_FETCH_GONE);
reporter.incrCounter("FetcherStatus", "robots_denied", 1);
continue;
} 将整段代码注释即可。
教程持续更新中。。。。
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