java/src/main/com/google/appengine/api/search/query/QueryTreeBuilder.java

   1 // Copyright 2011 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.search.query;
   4
   5 import org.antlr.runtime.ANTLRStringStream;
   6 import org.antlr.runtime.RecognitionException;
   7 import org.antlr.runtime.TokenRewriteStream;
   8 import org.antlr.runtime.tree.CommonTree;
   9 import org.antlr.runtime.tree.CommonTreeAdaptor;
  10
  11 /**
  12  * A generator of AST representation of a query. This class uses the given factory
  13  * to produce a query parser which parses user specified query. If successful it
  14  * returns the root of an AST representing the parsed query.
  15  *
  16  */
  17 public class QueryTreeBuilder {
  18
  19   private QueryParserFactory parserFactory;
  20   private final CommonTreeAdaptor adaptor = new CommonTreeAdaptor();
  21
  22   public QueryTreeBuilder() {
  23     this.parserFactory = new QueryParserFactory();
  24   }
  25
  26   public QueryTreeBuilder(QueryParserFactory parserFactory) {
  27     this.parserFactory = parserFactory;
  28   }
  29
  30   /**
  31    * Parses the user query and returns a CommonTree.
  32    *
  33    * @param query the user query to be parsed
  34    * @return a CommonTree constructed from the query
  35    * @throws RecognitionException if the user query is invalid
  36    * @throws NullPointerException if query is null
  37    */
  38   public CommonTree parse(String query) throws RecognitionException {
  39     if (query == null) {
  40       throw new NullPointerException("query must not be null");
  41     }
  42     String trimmed = query.trim();
  43     if (trimmed.isEmpty()) {
  44       return (CommonTree) adaptor.nil();
  45     }
  46     ANTLRStringStream stream = new ANTLRStringStream(query);
  47     QueryLexer lexer = new QueryLexer(stream);
  48     TokenRewriteStream tokens = new TokenRewriteStream(lexer);
  49     QueryParser parser = parserFactory.newParser(tokens);
  50     return (CommonTree) parser.query().getTree();
  51   }
  52 }