001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.conf;
019
020import java.io.IOException;
021import java.io.Writer;
022
023import javax.servlet.ServletException;
024import javax.servlet.http.HttpServlet;
025import javax.servlet.http.HttpServletRequest;
026import javax.servlet.http.HttpServletResponse;
027
028import org.apache.hadoop.classification.InterfaceAudience;
029import org.apache.hadoop.classification.InterfaceStability;
030import org.apache.hadoop.http.HttpServer2;
031
032/**
033 * A servlet to print out the running configuration data.
034 */
035@InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
036@InterfaceStability.Unstable
037public class ConfServlet extends HttpServlet {
038  private static final long serialVersionUID = 1L;
039
040  private static final String FORMAT_JSON = "json";
041  private static final String FORMAT_XML = "xml";
042  private static final String FORMAT_PARAM = "format";
043
044  /**
045   * Return the Configuration of the daemon hosting this servlet.
046   * This is populated when the HttpServer starts.
047   */
048  private Configuration getConfFromContext() {
049    Configuration conf = (Configuration)getServletContext().getAttribute(
050        HttpServer2.CONF_CONTEXT_ATTRIBUTE);
051    assert conf != null;
052    return conf;
053  }
054
055  @Override
056  public void doGet(HttpServletRequest request, HttpServletResponse response)
057      throws ServletException, IOException {
058
059    if (!HttpServer2.isInstrumentationAccessAllowed(getServletContext(),
060                                                   request, response)) {
061      return;
062    }
063
064    String format = request.getParameter(FORMAT_PARAM);
065    if (null == format) {
066      format = FORMAT_XML;
067    }
068
069    if (FORMAT_XML.equals(format)) {
070      response.setContentType("text/xml; charset=utf-8");
071    } else if (FORMAT_JSON.equals(format)) {
072      response.setContentType("application/json; charset=utf-8");
073    }
074
075    Writer out = response.getWriter();
076    try {
077      writeResponse(getConfFromContext(), out, format);
078    } catch (BadFormatException bfe) {
079      response.sendError(HttpServletResponse.SC_BAD_REQUEST, bfe.getMessage());
080    }
081    out.close();
082  }
083
084  /**
085   * Guts of the servlet - extracted for easy testing.
086   */
087  static void writeResponse(Configuration conf, Writer out, String format)
088    throws IOException, BadFormatException {
089    if (FORMAT_JSON.equals(format)) {
090      Configuration.dumpConfiguration(conf, out);
091    } else if (FORMAT_XML.equals(format)) {
092      conf.writeXml(out);
093    } else {
094      throw new BadFormatException("Bad format: " + format);
095    }
096  }
097
098  public static class BadFormatException extends Exception {
099    private static final long serialVersionUID = 1L;
100
101    public BadFormatException(String msg) {
102      super(msg);
103    }
104  }
105
106}