indexer-csv plugin is used for writing documents to a CSV file. It does not work in distributed mode, the output is written to the local filesystem, not to HDFS, see NUTCH-1541. The configuration for the index writers is on conf/index-writers.xml file, included in the official Nutch distribution and it's as follow:
<writer id="<writer_id>" class="org.apache.nutch.indexwriter.csv.CSVIndexWriter"> <mapping> ... </mapping> <parameters> ... </parameters> </writer>
Each <writer> element has two mandatory attributes:
<writer_id> is a unique identification for each configuration. This feature allows Nutch to distinguish each configuration, even when they are for the same index writer. In addition, it allows to have multiple instances for the same index writer, but with different configurations.
org.apache.nutch.indexwriter.csv.CSVIndexWriter corresponds to the canonical name of the class that implements the IndexWriter extension point. This value should not be modified for the indexer-csv plugin.
The mapping section is explained here. The structure of this section is general for all index writers.
Each parameter has the form <param name="<name>" value="<value>"/> and the parameters for this index writer are:
| Parameter Name | Description | Default value |
|---|---|---|
| fields | Ordered list of fields (columns) in the CSV file | id,title,content |
| charset | Encoding of CSV file | UTF-8 |
| separator | Separator between fields (columns) | , |
| valuesep | Separator between multiple values of one field | | |
| quotechar | Quote character used to quote fields containing separators or quotes | " |
| escapechar | Escape character used to escape a quote character | " |
| maxfieldlength | Max. length of a single field value in characters | 4096 |
| maxfieldvalues | Max. number of values of one field, useful for, e.g., the anchor texts field | 12 |
| header | Write CSV column headers | true |
| outpath | Output path / directory (local filesystem path, relative to current working directory) | csvindexwriter |