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 * <p> * http://www.apache.org/licenses/LICENSE-2.0 * <p> * 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.sentry.api.service.thrift; import org.apache.sentry.core.common.utils.PubSub; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter; import static org.apache.commons.lang.StringEscapeUtils.escapeHtml; /** * This servlet facilitates sending {topic, message } tuples to Servlet components * subscribed to specific topics. * <p> * It uses publish-subscribe mechanism implemented by PubSub class. * The form generated by this servlet consists of the following elements: * <p> * a) Topic: pull-down menu of existing topics, i.e. the topics registered with * PubSub by calling PubSub.subscribe() API. This prevents entering invalid topic. * <p> * b) Message: text field for entering a message * <p> * c) Submit: button to submit (topic, message) tuple * <p> * d) Status: text area printing status of the request or help information. */ public class PubSubServlet extends HttpServlet { private static final Logger LOGGER = LoggerFactory.getLogger(PubSubServlet.class); private static final String FORM_GET = "<!DOCTYPE html>" + "<html>" + "<body>" + "<form>" + "<br><br><b>Topic:</b><br><br>" + "<select name='topic'/>%s</select>" + "<br><br><b>Message:</b><br><br>" + "<input type='text' size='50' name='message'/>" + "<br><br>" + "<input type='submit' value='Submit'/>" + "</form>" + "<br><br><b>Status:</b><br><br>" + "<textarea rows='4' cols='50'>%s</textarea>" + "</body>" + "</html>"; /** * Return parameter on servlet request for the given name * * @param request: Servlet request * @param name: Name of parameter in servlet request * @return Parameter in servlet request for the given name, return null if can't find parameter. */ private static String getParameter(ServletRequest request, String name) { String s = request.getParameter(name); if (s == null) { return null; } s = s.trim(); return s.isEmpty() ? null : s; } /** * Parse the topic and message values and submit them via PubSub.submit() API. * Reject request for unknown topic, i.e. topic no one is subscribed to. */ @Override public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String topic = getParameter(request, "topic"); String message = getParameter(request, "message"); response.setContentType("text/html;charset=utf-8"); response.setStatus(HttpServletResponse.SC_OK); PrintWriter out = response.getWriter(); String msg = "Topic is required, Message is optional.\nValid topics: " + PubSub.getInstance().getTopics(); if (topic != null) { LOGGER.info("Submitting topic " + topic + ", message " + message); try { PubSub.getInstance().publish(PubSub.Topic.fromString(topic), message); msg = "Submitted topic " + topic + ", message " + message; } catch (Exception e) { msg = "Failed to submit topic " + topic + ", message " + message + " - " + e.getMessage(); LOGGER.error(msg); response.sendError(HttpServletResponse.SC_BAD_REQUEST, msg); return; } } StringBuilder topics = new StringBuilder(); for (PubSub.Topic t : PubSub.getInstance().getTopics()) { topics.append("<option>").append(t.getName()).append("</option>"); } String output = String.format(FORM_GET, topics.toString(), escapeHtml(msg)); if (LOGGER.isDebugEnabled()) { LOGGER.debug("HTML Page: " + output); } out.write(output); out.close(); response.flushBuffer(); } }