BaseContext.java

// =================================================================================================
// Copyright 2011 Twitter, Inc.
// -------------------------------------------------------------------------------------------------
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this work except in compliance with the License.
// You may obtain a copy of the License in the LICENSE file, or at:
//
//  http://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.twitter.common.thrift.text;

import com.google.gson.JsonElement;

import org.apache.thrift.TException;
import org.apache.thrift.protocol.TField;

/**
 * A base parsing context. Used as a root level parsing context for
 * parsing Json Objects
 *
 * @author Alex Roetter
 */
class BaseContext {

  /**
   * Called before we write an item
   */
  protected void write() {
  }

  /** Called before we read an item.
   */
  protected void read() {
  }

  /**
   * Thrift maps are made up of name value pairs, are we parsing a
   * thrift map name (e.g. left hand side of a map entry) here?
   */
  protected boolean isMapKey() {
    return false;
  }

  /**
   * Return the TField struct describing a Thrift struct item with
   * the given name.
   */
  protected TField getTFieldByName(String name) throws TException {
    return unsupportedOperation();
  }

  /**
   * Return the json element that should be processed next. Used for
   * Contexts that have child JsonElements, e.g. Sequences, Maps, etc.
   */
  protected JsonElement getCurrentChild() {
    return unsupportedOperation();
  }

  /**
   * Are there more child elements to process?
   */
  protected boolean hasMoreChildren() {
    return (Boolean) unsupportedOperation();
  }

  /**
   * Complain about a method called on a BaseContext that shouldn't have been.
   */
  private static <T> T unsupportedOperation() {
    throw new UnsupportedOperationException("Not supported by BaseContext.");
  }
}