#2101 HostURLFilter: drop the source host memoization shared by all fetcher threads (#2167) The last source URL, host and domain were kept in three plain instance fields and compared by identity. StatusEmitterBolt builds one URLFilters instance per bolt and FetcherBolt runs fetcher.threads.number threads through it, so those fields were written and read concurrently without any synchronisation, and the three writes were not atomic with each other. A thread could therefore see its own URL in previousSourceUrl next to another thread's host in previousSourceHost and compare the candidate against the wrong origin, dropping a same-host URL or admitting one outside the source host. The memoization only saved one PaidLevelDomain.getPLD call, so it is removed rather than synchronised.
Apache StormCrawler is an open source collection of resources for building low-latency, scalable web crawlers on Apache Storm. It is provided under Apache License and is written mostly in Java.
NOTE: These instructions assume that you have Apache Maven installed. You will need to install Apache Storm 3.1.0 to run the crawler.
StormCrawler requires Java 25 or above. To execute tests, it requires you to have a locally installed and working Docker environment.
Once Storm is installed, the easiest way to get started is to generate a new StormCrawler project following the instructions below:
mvn archetype:generate -DarchetypeGroupId=org.apache.stormcrawler -DarchetypeArtifactId=stormcrawler-archetype -DarchetypeVersion=<CURRENT_VERSION>
Be sure to replace <CURRENT_VERSION> with the latest released version, which you can find on search.maven.org.
You'll be asked to enter a groupId (e.g. com.mycompany.crawler), an artefactId (e.g. stormcrawler), a version, a package name and details about the user agent to use.
This will not only create a fully formed project containing a POM with the dependency above but also the default resource files, a default CrawlTopology class and a configuration file. Enter the directory you just created (should be the same as the artefactId you specified earlier) and follow the instructions on the README file.
Alternatively if you can‘t or don’t want to use the Maven archetype above, you can simply copy the files from archetype-resources.
Have a look at crawler.flux, the crawler-conf.yaml file as well as the files in src/main/resources/, they are all that is needed to run a crawl topology : all the other components come from the core module.
The documentation is a good place to start your investigations but if you are stuck please use the tag stormcrawler on StackOverflow or ask a question in the discussions section.
The project website has a page listing companies providing commercial support for Apache StormCrawler.
Please format your code before submitting a PR with
mvn git-code-format:format-code -Dgcf.globPattern="**/*" -Dskip.format.code=false
You can enable pre-commit format hooks by running:
mvn clean install -Dskip.format.code=false
The requirements for building from source are as follows
The build itself is straightforward:
mvn clean install
Note: We use some binary files for testing advanced crawler functionality. These files are located exclusively in the src/test directories of the respective modules.
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