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My passion is building crawlers and search engines. In particular, I specialize in building vertical search engines like Indeed.com, Homethinking.com, Bright.com and Enormo.com (all companies I've worked with). I've also worked on products such as Atlassian Jira and Confluence to improve their search capabilities. Kelvin has posted 22 posts at DZone. You can read more from them at their website. View Full User Profile

Create a Custom Solr QueryParser for Fun and Profit

12.24.2013
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In this post, I'll show you what you need to do to implement a custom Solr QueryParser.

Step 1

Extend the QParserPlugin:

public class TestQueryParserPlugin extends QParserPlugin {
  public void init(NamedList namedList) {
  }

  @Override public QParser createParser(String s, SolrParams localParams, SolrParams params, SolrQueryRequest req) {
    return new TestQParser(s, localParams, params, req);
  }
}

This is the class you'll define in solrconfig.xml, informing Solr of your queryparser. Define it like so:

<queryParser name="myfunparser" 
class="org.supermind.solr.queryparser.TestQParserPlugin"/>

Step 2

Extend QParser:

  public class TestQParser extends QParser {
    public TestQParser(String qstr, SolrParams localParams, SolrParams params, SolrQueryRequest req) {
      super(qstr, localParams, params, req);
    }

    @Override public Query parse() throws SyntaxError {
      return null;
    }
  }

Step 3

Actually implement the parsing in the parse() method.

Suppose we want to make a really simple parser for term queries, which are space-delimited. Here's how I'd do it:

@Override public Query parse() throws SyntaxError {
      String defaultField = req.getSchema().getDefaultSearchFieldName();
      QueryParser.Operator defaultOperator = QueryParser.Operator.valueOf(req.getSchema().getQueryParserDefaultOperator());
      BooleanClause.Occur op = (defaultOperator == QueryParser.Operator.AND) ? BooleanClause.Occur.MUST : BooleanClause.Occur.SHOULD;
      String[] arr = qstr.split(" ");
      BooleanQuery bq = new BooleanQuery(true);
      for(String s: arr) {
        if(s.trim().length() == 0) continue;
        bq.add(new TermQuery(new Term(defaultField, s)), op);
      }
      return bq;
    }

Step 4

In your query, use the nested query syntax to call your QueryParser:

http://localhost:8983/solr/collection1/select?q={!myfunparser}foo+bar+car

Maybe in a follow-up post I'll include the full code with jars and all.

Published at DZone with permission of its author, Kelvin Tan. (source)

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