com.google.appengine.api.search.query.ExpressionTreeBuilder Maven / Gradle / Ivy

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/*
 * Copyright 2021 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.appengine.api.search.query;

import org.antlr.runtime.ANTLRStringStream;
import org.antlr.runtime.RecognitionException;
import org.antlr.runtime.TokenRewriteStream;
import org.antlr.runtime.tree.CommonTree;
import org.antlr.runtime.tree.CommonTreeAdaptor;

/**
 * A generator of AST representation of an expression. This class can use an
 * optionally supplied CommonTreeAdaptor to process the tree further.
 * If successful it returns the root of an AST representing the parsed query.
 *
 */
public class ExpressionTreeBuilder {
  private final CommonTreeAdaptor adaptor;

  public ExpressionTreeBuilder() {
    this(new CommonTreeAdaptor());
  }

  public ExpressionTreeBuilder(CommonTreeAdaptor adaptor) {
    this.adaptor = adaptor;
  }

  /**
   * Parses the user expression and returns a {@link CommonTree}.
   *
   * @param expression the expression to parse
   * @return a CommonTree constructed from the expression
   * @throws RecognitionException if the user expression is invalid
   */
  public CommonTree parse(String expression) throws RecognitionException {
    ANTLRStringStream stream = new ANTLRStringStream(expression);
    ExpressionLexer lexer = new ExpressionLexer(stream);
    TokenRewriteStream tokens = new TokenRewriteStream(lexer);
    ExpressionParser parser = new ExpressionParser(tokens);
    parser.setTreeAdaptor(adaptor);
    return (CommonTree) parser.expression().getTree();
  }
}