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.jmx; import java.io.IOException; import java.io.PrintWriter; import java.lang.management.ManagementFactory; import java.lang.reflect.Array; import java.util.Iterator; import java.util.Set; import javax.management.AttributeNotFoundException; import javax.management.InstanceNotFoundException; import javax.management.IntrospectionException; import javax.management.MBeanAttributeInfo; import javax.management.MBeanException; import javax.management.MBeanInfo; import javax.management.MBeanServer; import javax.management.MalformedObjectNameException; import javax.management.ObjectName; import javax.management.ReflectionException; import javax.management.RuntimeMBeanException; import javax.management.openmbean.CompositeData; import javax.management.openmbean.CompositeType; 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.http.HttpServer; import org.codehaus.jackson.JsonFactory; import org.codehaus.jackson.JsonGenerator; /* * 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> * For example <code>http://.../jmx?qry=Hadoop:*</code> will return * all hadoop metrics exposed through JMX. * <p> * If the <code>qry</code> parameter is not formatted correctly then a * 400 BAD REQUEST http response code will be returned. * <p> * The return format is JSON and in the form * <p> * <code><pre> * { * "beans" : [ * { * "name":"bean-name" * ... * } * ] * } * </pre></code> * <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. */ public class JMXJsonServlet extends HttpServlet { private static final Log LOG = LogFactory.getLog(JMXJsonServlet.class); private static final long serialVersionUID = 1L; // ----------------------------------------------------- Instance Variables /** * MBean server. */ protected transient MBeanServer mBeanServer = null; // --------------------------------------------------------- Public Methods /** * Initialize this servlet. */ @Override public void init() throws ServletException { // Retrieve the MBean server mBeanServer = ManagementFactory.getPlatformMBeanServer(); } /** * 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 { // Do the authorization if (!HttpServer.hasAdministratorAccess(getServletContext(), request, response)) { return; } response.setContentType("application/json; charset=utf8"); PrintWriter writer = response.getWriter(); JsonFactory jsonFactory = new JsonFactory(); JsonGenerator jg = jsonFactory.createJsonGenerator(writer); jg.useDefaultPrettyPrinter(); jg.writeStartObject(); if (mBeanServer == null) { jg.writeStringField("result", "ERROR"); jg.writeStringField("message", "No MBeanServer could be found"); jg.close(); return; } String qry = request.getParameter("qry"); if (qry == null) { qry = "*:*"; } listBeans(jg, new ObjectName(qry)); jg.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); } } // --------------------------------------------------------- Private Methods private void listBeans(JsonGenerator jg, ObjectName qry) throws IOException { LOG.debug("Listing beans for " + qry); Set<ObjectName> names = null; names = mBeanServer.queryNames(qry, null); jg.writeArrayFieldStart("beans"); Iterator<ObjectName> it = names.iterator(); while (it.hasNext()) { ObjectName oname = it.next(); MBeanInfo minfo; String code; try { minfo = mBeanServer.getMBeanInfo(oname); code = minfo.getClassName(); try { if ("org.apache.commons.modeler.BaseModelMBean".equals(code)) { code = (String) mBeanServer.getAttribute(oname, "modelerType"); } } catch (AttributeNotFoundException e) { //Ignored the modelerType attribute was not found, so use the class name instead. } catch (MBeanException e) { //The code inside the attribute getter threw an exception so log it, and // fall back on the class name LOG.error("getting attribute modelerType of " + oname + " threw an exception", e); } catch (RuntimeException e) { //For some reason even with an MBeanException available to them Runtime exceptions //can still find their way through, so treat them the same as MBeanException LOG.error("getting attribute modelerType of " + oname + " threw an exception", e); } catch (ReflectionException e) { //This happens when the code inside the JMX bean (setter?? from the java docs) //threw an exception, so log it and fall back on the class name LOG.error("getting attribute modelerType of " + oname + " threw an exception", e); } } catch (InstanceNotFoundException e) { //Ignored for some reason the bean was not found so don't output it continue; } catch (IntrospectionException e) { //This is an internal error, something odd happened with reflection so log it and //don't output the bean. LOG.error("Problem while trying to process JMX query: " + qry + " with MBean " + oname, e); continue; } catch (ReflectionException e) { //This happens when the code inside the JMX bean threw an exception, so log it and //don't output the bean. LOG.error("Problem while trying to process JMX query: " + qry + " with MBean " + oname, e); continue; } jg.writeStartObject(); jg.writeStringField("name", oname.toString()); // can't be null - I think jg.writeStringField("modelerType", code); MBeanAttributeInfo attrs[] = minfo.getAttributes(); for (int i = 0; i < attrs.length; i++) { writeAttribute(jg, oname, attrs[i]); } // LOG.error("Caught Error writing value ",t); // ExceptionUtils.handleThrowable(t); //} jg.writeEndObject(); } jg.writeEndArray(); } private void writeAttribute(JsonGenerator jg, ObjectName oname, MBeanAttributeInfo attr) throws IOException { if (!attr.isReadable()) { return; } String attName = attr.getName(); if ("modelerType".equals(attName)) { return; } if (attName.indexOf("=") >= 0 || attName.indexOf(":") >= 0 || attName.indexOf(" ") >= 0) { return; } Object value = null; try { value = mBeanServer.getAttribute(oname, attName); } catch (RuntimeMBeanException e) { // UnsupportedOperationExceptions happen in the normal course of business, // so no need to log them as errors all the time. if (e.getCause() instanceof UnsupportedOperationException) { LOG.debug("getting attribute " + attName + " of " + oname + " threw an exception", e); } else { LOG.error("getting attribute " + attName + " of " + oname + " threw an exception", e); } return; } catch (AttributeNotFoundException e) { //Ignored the attribute was not found, which should never happen because the bean //just told us that it has this attribute, but if this happens just don't output //the attribute. return; } catch (MBeanException e) { //The code inside the attribute getter threw an exception so log it, and // skip outputting the attribute LOG.error("getting attribute " + attName + " of " + oname + " threw an exception", e); return; } catch (RuntimeException e) { //For some reason even with an MBeanException available to them Runtime exceptions //can still find their way through, so treat them the same as MBeanException LOG.error("getting attribute " + attName + " of " + oname + " threw an exception", e); return; } catch (ReflectionException e) { //This happens when the code inside the JMX bean (setter?? from the java docs) //threw an exception, so log it and skip outputting the attribute LOG.error("getting attribute " + attName + " of " + oname + " threw an exception", e); return; } catch (InstanceNotFoundException e) { //Ignored the mbean itself was not found, which should never happen because we //just accessed it (perhaps something unregistered in-between) but if this //happens just don't output the attribute. return; } writeAttribute(jg, attName, value); } private void writeAttribute(JsonGenerator jg, String attName, Object value) throws IOException { jg.writeFieldName(attName); writeObject(jg, value); } private void writeObject(JsonGenerator jg, Object value) throws IOException { if (value == null) { jg.writeNull(); } else { Class<?> c = value.getClass(); if (c.isArray()) { jg.writeStartArray(); int len = Array.getLength(value); for (int j = 0; j < len; j++) { Object item = Array.get(value, j); writeObject(jg, item); } jg.writeEndArray(); } else if (value instanceof Number) { Number n = (Number) value; jg.writeNumber(n.toString()); } else if (value instanceof Boolean) { Boolean b = (Boolean) value; jg.writeBoolean(b); } else if (value instanceof CompositeData) { CompositeData cds = (CompositeData) value; CompositeType comp = cds.getCompositeType(); Set<String> keys = comp.keySet(); jg.writeStartObject(); for (String key : keys) { writeAttribute(jg, key, cds.get(key)); } jg.writeEndObject(); } else if (value instanceof TabularData) { TabularData tds = (TabularData) value; jg.writeStartArray(); for (Object entry : tds.values()) { writeObject(jg, entry); } jg.writeEndArray(); } else { jg.writeString(value.toString()); } } } }