Run Nutch In Eclipse on Linux and Windows nutch version 1.0

参考官方文档，通过努力终于我nutch在eclispe下跑通了：），真的很好，很详细，不知道自己有没耐心些这样的文章：）
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Tested with
Nutch release 1.0

Eclipse 3.3 (Europa) and 3.4 (Ganymede)

Java 1.6

Ubuntu (should work on most platforms though)

Windows XP and Vista

Before you start
Setting up Nutch to run into Eclipse can be tricky, and most of the time it is much faster if you edit Nutch in Eclipse but run the scripts from the command line (my 2 cents). However, it's very useful to be able to debug Nutch in Eclipse. Sometimes examining the logs (logs/hadoop.log) is quicker to debug a problem.

Steps
For Windows Users
If you are running Windows (tested on Windows XP) you must first install cygwin. Download it from  http://www.cygwin.com/setup.exe

Install cygwin and set the PATH environment variable for it. You can set it from the Control Panel, System, Advanced Tab, Environment Variables and edit/add PATH.

Example PATH:

C:\Sun\SDK\bin;C:\cygwin\bin
If you run "bash" from the Windows command line (Start > Run... > cmd.exe) it should successfully run cygwin.

If you are running Eclipse on Vista, you will need to either give cygwin administrative privileges or  turn off Vista's User Access Control (UAC). Otherwise Hadoop will likely complain that it cannot change a directory permission when you later run the crawler:

org.apache.hadoop.util.Shell$ExitCodeException: chmod: changing permissions of ... Permission denied
See  this for more information about the UAC issue.

Install Nutch
Grab a  fresh release of Nutch 1.0 or download and untar the  official 1.0 release.

Do not build Nutch yet. Make sure you have no .project and .classpath files in the Nutch directory

Create a new Java Project in Eclipse
File > New > Project > Java project > click Next

Name the project (Nutch_Trunk for instance)

Select "Create project from existing source" and use the location where you downloaded Nutch

Click on Next, and wait while Eclipse is scanning the folders

Add the folder "conf" to the classpath (click the "Libraries" tab, click "Add Class Folder..." button, and select "conf" from the list)

Go to "Order and Export" tab, find the entry for added "conf" folder and move it to the top (by checking it and clicking the "Top" button). This is required so Eclipse will take config (nutch-default.xml, nutch-final.xml, etc.) resources from our "conf" folder and not from somewhere else.

Eclipse should have guessed all the Java files that must be added to your classpath. If that's not the case, add "src/java", "src/test" and all plugin "src/java" and "src/test" folders to your source folders. Also add all jars in "lib" and in the plugin lib folders to your libraries

Click the "Source" tab and set the default output folder to "Nutch_Trunk/bin/tmp_build". (You may need to create the tmp_build folder.)

Click the "Finish" button

DO NOT add "build" to classpath

Configure Nutch
See the  Tutorial

Change the property "plugin.folders" to "./src/plugin" on $NUTCH_HOME/conf/nutch-defaul.xml

Make sure Nutch is configured correctly before testing it into Eclipse 

Missing org.farng and com.etranslate
Eclipse will complain about some import statements in parse-mp3 and parse-rtf plugins (30 errors in my case). Because of incompatibility with the Apache license, the .jar files that define the necessary classes were not included with the source code.

Download them here:

http://nutch.cvs.sourceforge.net/nutch/nutch/src/plugin/parse-mp3/lib/

http://nutch.cvs.sourceforge.net/nutch/nutch/src/plugin/parse-rtf/lib/

Copy the jar files into src/plugin/parse-mp3/lib and src/plugin/parse-rtf/lib/ respectively. Then add the jar files to the build path (First refresh the workspace by pressing F5. Then right-click the project folder > Build Path > Configure Build Path... Then select the Libraries tab, click "Add Jars..." and then add each .jar file individually).

Two Errors with RTFParseFactory
If you are trying to build the official 1.0 release, Eclipse will complain about 2 errors regarding the RTFParseFactory (this is after adding the RTF jar file from the previous step). This problem was fixed (see  NUTCH-644 and  NUTCH-705) but was not included in the 1.0 official release because of licensing issues. So you will need to manually alter the code to remove these 2 build errors.

In RTFParseFactory.java:

Add the following import statement: import org.apache.nutch.parse.ParseResult;

Change

public Parse getParse(Content content) {
to

public ParseResult getParse(Content content) {
In the getParse function, replace

return new ParseStatus(ParseStatus.FAILED,
                               ParseStatus.FAILED_EXCEPTION,
                               e.toString()).getEmptyParse(conf);
with

return new ParseStatus(ParseStatus.FAILED,
                ParseStatus.FAILED_EXCEPTION,
              e.toString()).getEmptyParseResult(content.getUrl(), getConf());
In the getParse function, replace

return new ParseImpl(text,
                         new ParseData(ParseStatus.STATUS_SUCCESS,
                                       title,
                                       OutlinkExtractor.getOutlinks(text, this.conf),
                                       content.getMetadata(),
                                       metadata));
with

return ParseResult.createParseResult(content.getUrl(),
                             new ParseImpl(text,
                                     new ParseData(ParseStatus.STATUS_SUCCESS,
                                             title,
                                             OutlinkExtractor.getOutlinks(text, this.conf),
                                             content.getMetadata(),
                                             metadata)));

In TestRTFParser.java, replace

parse = new ParseUtil(conf).parseByExtensionId("parse-rtf", content);
with

parse = new ParseUtil(conf).parseByExtensionId("parse-rtf", content).get(urlString);
Once you have made these changes and saved the files, Eclipse should build with no errors.

Build Nutch
If you setup the project correctly, Eclipse will build Nutch for you into "tmp_build". See below for problems you could run into.

Create Eclipse launcher
Menu Run > "Run..."

create "New" for "Java Application"

set in Main class

org.apache.nutch.crawl.Crawl
on tab Arguments, Program Arguments

urls -dir crawl -depth 3 -topN 50
in VM arguments

-Dhadoop.log.dir=logs -Dhadoop.log.file=hadoop.log
click on "Run"

if all works, you should see Nutch getting busy at crawling 

Debug Nutch in Eclipse (not yet tested for 0.9)
Set breakpoints and debug a crawl

It can be tricky to find out where to set the breakpoint, because of the Hadoop jobs. Here are a few good places to set breakpoints:

Fetcher [line: 371] - run
Fetcher [line: 438] - fetch
Fetcher$FetcherThread [line: 149] - run()
Generator [line: 281] - generate
Generator$Selector [line: 119] - map
OutlinkExtractor [line: 111] - getOutlinks
If things do not work...
Yes, Nutch and Eclipse can be a difficult companionship sometimes 

Java Heap Size problem
If the crawler throws an IOException exception early in the crawl (Exception in thread "main" java.io.IOException: Job failed!), check the logs/hadoop.log file for further information. If you find in hadoop.log lines similar to this:

2009-04-13 13:41:06,105 WARN  mapred.LocalJobRunner - job_local_0001
java.lang.OutOfMemoryError: Java heap space
then you should increase amount of RAM for running applications from Eclipse.

Just set it in:

Eclipse -> Window -> Preferences -> Java -> Installed JREs -> edit -> Default VM arguments

I've set mine to

-Xms5m -Xmx150m
because I have like 200MB RAM left after running all apps

-Xms (minimum ammount of RAM memory for running applications) -Xmx (maximum)

Eclipse: Cannot create project content in workspace
The nutch source code must be out of the workspace folder. My first attempt was download the code with eclipse (svn) under my workspace. When I try to create the project using existing code, eclipse don't let me do it from source code into the workspace. I use the source code out of my workspace and it work fine.

plugin dir not found
Make sure you set your plugin.folders property correct, instead of using a relative path you can use a absolute one as well in nutch-defaults.xml or may be better in nutch-site.xml

<property>
  <name>plugin.folders</name>
  <value>/home/....../nutch-0.9/src/plugin</value>
No plugins loaded during unit tests in Eclipse
During unit testing, Eclipse ignored conf/nutch-site.xml in favor of src/test/nutch-site.xml, so you might need to add the plugin directory configuration to that file as well.

Unit tests work in eclipse but fail when running ant in the command line
Suppose your unit tests work perfectly in eclipse, but each and everyone fail when running ant test in the command line - including the ones you haven't modified. Check if you defined the plugin.folders property in hadoop-site.xml. In that case, try removing it from that file and adding it directly to nutch-site.xml

Run ant test again. That should have solved the problem.

If that didn't solve the problem, are you testing a plugin? If so, did you add the plugin to the list of packages in plugin\build.xml, on the test target?

classNotFound
open the class itself, rightclick

refresh the build dir

debugging hadoop classes
Sometime it makes sense to also have the hadoop classes available during debugging. So, you can check out the Hadoop sources on your machine and add the sources to the hadoop-xxx.jar. Alternatively, you can:

Remove the hadoopXXX.jar from your classpath libraries

Checkout the hadoop brunch that is used within nutch

configure a hadoop project similar to the nutch project within your eclipse

add the hadoop project as a dependent project of nutch project

you can now also set break points within hadoop classes lik inputformat implementations etc.

Failed to get the current user's information
On Windows, if the crawler throws an exception complaining it "Failed to get the current user's information" or 'Login failed: Cannot run program "bash"', it is likely you forgot to set the PATH to point to cygwin. Open a new command line window (All Programs > Accessories > Command Prompt) and type "bash". This should start cygwin. If it doesn't, type "path" to see your path. You should see within the path the cygwin bin directory (e.g., C:\cygwin\bin). See the steps to adding this to your PATH at the top of the article under "For Windows Users". After setting the PATH, you will likely need to restart Eclipse so it will use the new PATH.

Original credits: RenaudRichardet