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

   1 package com.google.appengine.api.search.query;
   2
   3 import com.google.common.base.Preconditions;
   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 public class QueryTreeBuilder {
  17   private static final ThreadLocal<QueryLexer> LEXER_POOL = new ThreadLocal<QueryLexer>() {
  18     @Override
  19     protected QueryLexer initialValue() {
  20       return new QueryLexer();
  21     }
  22   };
  23
  24   private final QueryParserFactory parserFactory;
  25   private final CommonTreeAdaptor adaptor = new CommonTreeAdaptor();
  26
  27   public QueryTreeBuilder() {
  28     this.parserFactory = new QueryParserFactory();
  29   }
  30
  31   public QueryTreeBuilder(QueryParserFactory parserFactory) {
  32     this.parserFactory = parserFactory;
  33   }
  34
  35   /**
  36    * Parses the user query and returns its AST.
  37    *
  38    * @param query the user query to be parsed
  39    * @return a CommonTree constructed from the query
  40    * @throws RecognitionException if the user query is invalid
  41    * @throws NullPointerException if query is null
  42    */
  43   public CommonTree parse(String query) throws RecognitionException {
  44     Preconditions.checkNotNull(query, "query must not be null");
  45     ANTLRStringStream stream = new ANTLRStringStream(query);
  46     QueryLexer lexer = LEXER_POOL.get();
  47     lexer.setCharStream(stream);
  48     TokenRewriteStream tokens = new TokenRewriteStream(lexer);
  49     QueryParser parser = parserFactory.newParser(tokens);
  50     CommonTree tree =  (CommonTree) parser.query().getTree();
  51     if (tree.getType() == QueryParser.EMPTY && tree.getChildCount() == 0) {
  52       tree = (CommonTree) adaptor.nil();
  53     }
  54     return tree;
  55   }
  56 }