net.lshift.diffa.participant.scanning.ScanningParticipantServlet Maven / Gradle / Ivy

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/**
 * Copyright (C) 2010-2011 LShift Ltd.
 *
 * 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
 *
 *         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 net.lshift.diffa.participant.scanning;

import net.lshift.diffa.participant.common.JSONHelper;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * Base support servlet for implementing a Diffa scanning participant.
 */
public abstract class ScanningParticipantServlet extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {

    List constraints = determineConstraints(req);
    List aggregations = determineAggregations(req);

    List entries = doQuery(constraints, aggregations);
    resp.setContentType("application/json");
    JSONHelper.writeQueryResult(resp.getOutputStream(), entries);
  }

  /**
   * Callback to be implemented by sub-classes to determine the constraints relevant to a request.
   * @param req the request to check for constraints.
   * @return the constraints. Default implementation is to return no constraints.
   */
  protected List determineConstraints(HttpServletRequest req) {
    return new ArrayList();
  }

  /**
   * Callback to be implemented by sub-classes to determine the aggregations relevant to a request.
   * @param req the request to check for aggregations.
   * @return the aggregations. Default implementation is to return no aggregations.
   */
  protected List determineAggregations(HttpServletRequest req) {
    return new ArrayList();
  }

  /**
   * Callback to be implemented by sub-classes to query for data relevant to this query.
   * @param constraints the constraints to apply.
   * @param aggregations the aggregations to apply.
   * @return the result entries.
   */
  protected abstract List doQuery(List constraints, List aggregations);
}