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     */
018    package org.apache.hadoop.conf;
019    
020    import java.io.IOException;
021    import java.io.OutputStreamWriter;
022    import java.io.Writer;
023    
024    import javax.servlet.ServletException;
025    import javax.servlet.http.HttpServlet;
026    import javax.servlet.http.HttpServletRequest;
027    import javax.servlet.http.HttpServletResponse;
028    
029    import org.apache.hadoop.classification.InterfaceAudience;
030    import org.apache.hadoop.classification.InterfaceStability;
031    import org.apache.hadoop.http.HttpServer;
032    
033    /**
034     * A servlet to print out the running configuration data.
035     */
036    @InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
037    @InterfaceStability.Unstable
038    public class ConfServlet extends HttpServlet {
039      private static final long serialVersionUID = 1L;
040    
041      private static final String FORMAT_JSON = "json";
042      private static final String FORMAT_XML = "xml";
043      private static final String FORMAT_PARAM = "format";
044    
045      /**
046       * Return the Configuration of the daemon hosting this servlet.
047       * This is populated when the HttpServer starts.
048       */
049      private Configuration getConfFromContext() {
050        Configuration conf = (Configuration)getServletContext().getAttribute(
051            HttpServer.CONF_CONTEXT_ATTRIBUTE);
052        assert conf != null;
053        return conf;
054      }
055    
056      @Override
057      public void doGet(HttpServletRequest request, HttpServletResponse response)
058          throws ServletException, IOException {
059    
060        // Do the authorization
061        if (!HttpServer.hasAdministratorAccess(getServletContext(), request,
062            response)) {
063          return;
064        }
065    
066        String format = request.getParameter(FORMAT_PARAM);
067        if (null == format) {
068          format = FORMAT_XML;
069        }
070    
071        if (FORMAT_XML.equals(format)) {
072          response.setContentType("text/xml; charset=utf-8");
073        } else if (FORMAT_JSON.equals(format)) {
074          response.setContentType("application/json; charset=utf-8");
075        }
076    
077        Writer out = response.getWriter();
078        try {
079          writeResponse(getConfFromContext(), out, format);
080        } catch (BadFormatException bfe) {
081          response.sendError(HttpServletResponse.SC_BAD_REQUEST, bfe.getMessage());
082        }
083        out.close();
084      }
085    
086      /**
087       * Guts of the servlet - extracted for easy testing.
088       */
089      static void writeResponse(Configuration conf, Writer out, String format)
090        throws IOException, BadFormatException {
091        if (FORMAT_JSON.equals(format)) {
092          Configuration.dumpConfiguration(conf, out);
093        } else if (FORMAT_XML.equals(format)) {
094          conf.writeXml(out);
095        } else {
096          throw new BadFormatException("Bad format: " + format);
097        }
098      }
099    
100      public static class BadFormatException extends Exception {
101        private static final long serialVersionUID = 1L;
102    
103        public BadFormatException(String msg) {
104          super(msg);
105        }
106      }
107    
108    }