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.hadoop.hbase.http.jmx; import java.io.IOException; import java.io.PrintWriter; import java.lang.management.ManagementFactory; import javax.management.MBeanServer; import javax.management.MalformedObjectNameException; import javax.management.ObjectName; import javax.management.openmbean.CompositeData; import javax.management.openmbean.TabularData; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.hbase.http.HttpServer; import org.apache.hadoop.hbase.util.JSONBean; /* * This servlet is based off of the JMXProxyServlet from Tomcat 7.0.14. It has * been rewritten to be read only and to output in a JSON format so it is not * really that close to the original. */ /** * Provides Read only web access to JMX. * <p> * This servlet generally will be placed under the /jmx URL for each * HttpServer. It provides read only * access to JMX metrics. The optional <code>qry</code> parameter * may be used to query only a subset of the JMX Beans. This query * functionality is provided through the * {@link MBeanServer#queryNames(ObjectName, javax.management.QueryExp)} * method. * </p> * <p> * For example <code>http://.../jmx?qry=Hadoop:*</code> will return * all hadoop metrics exposed through JMX. * </p> * <p> * The optional <code>get</code> parameter is used to query an specific * attribute of a JMX bean. The format of the URL is * <code>http://.../jmx?get=MXBeanName::AttributeName</code> * </p> * <p> * For example * <code> * http://../jmx?get=Hadoop:service=NameNode,name=NameNodeInfo::ClusterId * </code> will return the cluster id of the namenode mxbean. * </p> * <p> * If the <code>qry</code> or the <code>get</code> parameter is not formatted * correctly then a 400 BAD REQUEST http response code will be returned. * </p> * <p> * If a resouce such as a mbean or attribute can not be found, * a 404 SC_NOT_FOUND http response code will be returned. * </p> * <p> * The return format is JSON and in the form * </p> * <pre><code> * { * "beans" : [ * { * "name":"bean-name" * ... * } * ] * } * </code></pre> * <p> * The servlet attempts to convert the the JMXBeans into JSON. Each * bean's attributes will be converted to a JSON object member. * * If the attribute is a boolean, a number, a string, or an array * it will be converted to the JSON equivalent. * * If the value is a {@link CompositeData} then it will be converted * to a JSON object with the keys as the name of the JSON member and * the value is converted following these same rules. * * If the value is a {@link TabularData} then it will be converted * to an array of the {@link CompositeData} elements that it contains. * * All other objects will be converted to a string and output as such. * * The bean's name and modelerType will be returned for all beans. * * Optional paramater "callback" should be used to deliver JSONP response. * </p> * */ public class JMXJsonServlet extends HttpServlet { private static final Log LOG = LogFactory.getLog(JMXJsonServlet.class); private static final long serialVersionUID = 1L; private static final String CALLBACK_PARAM = "callback"; /** * If query string includes 'description', then we will emit bean and attribute descriptions to * output IFF they are not null and IFF the description is not the same as the attribute name: * i.e. specify an URL like so: /jmx?description=true */ private static final String INCLUDE_DESCRIPTION = "description"; /** * MBean server. */ protected transient MBeanServer mBeanServer; protected transient JSONBean jsonBeanWriter; /** * Initialize this servlet. */ @Override public void init() throws ServletException { // Retrieve the MBean server mBeanServer = ManagementFactory.getPlatformMBeanServer(); this.jsonBeanWriter = new JSONBean(); } /** * Process a GET request for the specified resource. * * @param request * The servlet request we are processing * @param response * The servlet response we are creating */ @Override public void doGet(HttpServletRequest request, HttpServletResponse response) { try { if (!HttpServer.isInstrumentationAccessAllowed(getServletContext(), request, response)) { return; } String jsonpcb = null; PrintWriter writer = null; JSONBean.Writer beanWriter = null; try { writer = response.getWriter(); beanWriter = this.jsonBeanWriter.open(writer); // "callback" parameter implies JSONP outpout jsonpcb = request.getParameter(CALLBACK_PARAM); if (jsonpcb != null) { response.setContentType("application/javascript; charset=utf8"); writer.write(jsonpcb + "("); } else { response.setContentType("application/json; charset=utf8"); } // Should we output description on each attribute and bean? String tmpStr = request.getParameter(INCLUDE_DESCRIPTION); boolean description = tmpStr != null && tmpStr.length() > 0; // query per mbean attribute String getmethod = request.getParameter("get"); if (getmethod != null) { String[] splitStrings = getmethod.split("\\:\\:"); if (splitStrings.length != 2) { beanWriter.write("result", "ERROR"); beanWriter.write("message", "query format is not as expected."); beanWriter.flush(); response.setStatus(HttpServletResponse.SC_BAD_REQUEST); return; } if (beanWriter.write(this.mBeanServer, new ObjectName(splitStrings[0]), splitStrings[1], description) != 0) { beanWriter.flush(); response.setStatus(HttpServletResponse.SC_BAD_REQUEST); } return; } // query per mbean String qry = request.getParameter("qry"); if (qry == null) { qry = "*:*"; } if (beanWriter.write(this.mBeanServer, new ObjectName(qry), null, description) != 0) { beanWriter.flush(); response.setStatus(HttpServletResponse.SC_BAD_REQUEST); } } finally { if (beanWriter != null) beanWriter.close(); if (jsonpcb != null) { writer.write(");"); } if (writer != null) { writer.close(); } } } catch (IOException e) { LOG.error("Caught an exception while processing JMX request", e); response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); } catch (MalformedObjectNameException e) { LOG.error("Caught an exception while processing JMX request", e); response.setStatus(HttpServletResponse.SC_BAD_REQUEST); } } }