java/src/main/com/google/appengine/api/search/ExpressionTreeBuilder.java

   1 // Copyright 2011 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.search;
   4
   5 import com.google.apphosting.api.AppEngineInternal;
   6
   7 import org.antlr.runtime.ANTLRStringStream;
   8 import org.antlr.runtime.RecognitionException;
   9 import org.antlr.runtime.TokenRewriteStream;
  10 import org.antlr.runtime.tree.CommonTree;
  11 import org.antlr.runtime.tree.CommonTreeAdaptor;
  12
  13 /**
  14  * A generator of AST representation of an expression. This class can use an
  15  * optionally supplied CommonTreeAdaptor to process the tree further.
  16  * If successful it returns the root of an AST representing the parsed query.
  17  *
  18  */
  19 @AppEngineInternal
  20 public class ExpressionTreeBuilder {
  21   private final CommonTreeAdaptor adaptor;
  22
  23   public ExpressionTreeBuilder() {
  24     this(new CommonTreeAdaptor());
  25   }
  26
  27   public ExpressionTreeBuilder(CommonTreeAdaptor adaptor) {
  28     this.adaptor = adaptor;
  29   }
  30
  31   /**
  32    * Parses the user expression and returns a {@link CommonTree}.
  33    *
  34    * @param expression the expression to parse
  35    * @return a CommonTree constructed from the expression
  36    * @throws RecognitionException if the user expression is invalid
  37    */
  38   public CommonTree parse(String expression) throws RecognitionException {
  39     ANTLRStringStream stream = new ANTLRStringStream(expression);
  40     ExpressionLexer lexer = new ExpressionLexer(stream);
  41     TokenRewriteStream tokens = new TokenRewriteStream(lexer);
  42     ExpressionParser parser = new ExpressionParser(tokens);
  43     parser.setTreeAdaptor(adaptor);
  44     return (CommonTree) parser.expression().getTree();
  45   }
  46 }