Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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 org.apache.ambari.view.tez; import org.apache.ambari.view.URLConnectionProvider; import org.apache.ambari.view.ViewContext; import org.apache.commons.io.IOUtils; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import javax.servlet.ServletConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.ws.rs.HttpMethod; import javax.ws.rs.core.Response; import javax.ws.rs.core.Response.Status; import java.net.HttpURLConnection; import java.net.URLDecoder; import java.util.Collections; import java.util.Map; /** * Simple servlet for proxying requests with doAs impersonation. */ public class ProxyServlet extends HttpServlet { private static final Logger LOG = LoggerFactory.getLogger(ProxyServlet.class); private URLConnectionProvider urlConnectionProvider; private final static String nullData = null; private final static Map<String, String> emptyHeaders = Collections.EMPTY_MAP; @Override public void init(ServletConfig config) throws ServletException { super.init(config); ServletContext context = config.getServletContext(); ViewContext viewContext = (ViewContext) context.getAttribute(ViewContext.CONTEXT_ATTRIBUTE); this.urlConnectionProvider = viewContext.getURLConnectionProvider(); } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { String urlToRead = URLDecoder.decode(request.getParameter("url")); response.setContentType(request.getContentType()); if (LOG.isDebugEnabled()) { LOG.debug("Requesting data from ATS, url=" + urlToRead); } InputStream resultInputStream; String result = ""; // When in doubt, assume error int responseCode = Status.INTERNAL_SERVER_ERROR.getStatusCode(); HttpURLConnection connection; try { // Use nullData as null string and null inputstream cannot be disambiguated // URL Stream Provider will automatically inject the doAs param with the current // user's info connection = urlConnectionProvider.getConnectionAsCurrent(urlToRead, HttpMethod.GET, nullData, emptyHeaders); responseCode = connection.getResponseCode(); if (LOG.isDebugEnabled()) { LOG.debug("Received response from ATS, url=" + urlToRead + ", responseCode=" + responseCode); } if (responseCode >= Response.Status.BAD_REQUEST.getStatusCode()) { resultInputStream = connection.getErrorStream(); } else { resultInputStream = connection.getInputStream(); } result = IOUtils.toString(resultInputStream); if (LOG.isDebugEnabled()) { LOG.debug("Received response from ATS, url=" + urlToRead + ", responseCode=" + responseCode + ", responseBodyLen=" + result.length()); } } catch (IOException e) { // We might kill the ambari server by logging this error every time a call fails if (LOG.isDebugEnabled()) { LOG.warn("Failed to retrieve data from ATS, url=" + urlToRead, e); } responseCode = Status.INTERNAL_SERVER_ERROR.getStatusCode(); result = e.toString(); } catch (Exception e) { LOG.warn("Unknown Exception: Failed to retrieve data from ATS, url=" + urlToRead, e); responseCode = Status.INTERNAL_SERVER_ERROR.getStatusCode(); result = e.toString(); } finally { // not disconnecting http conn as it might be cached/re-used internally // in the UrlStreamProvider } response.setStatus(responseCode); if (result != null) { PrintWriter writer = response.getWriter(); writer.print(result); } } }