Java tutorial
/** * Copyright 2015 StreamSets Inc. * * Licensed under 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 com.streamsets.datacollector.http; import com.fasterxml.jackson.core.JsonFactory; import com.fasterxml.jackson.core.JsonGenerator; 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.RuntimeErrorException; 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 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; /** * Variant of Hadoop's JMXJsonServlet. * <p/> * CHANGES: removed commons-logging and other Hadoop dependencies. */ public class JMXJsonServlet extends HttpServlet { private static final long serialVersionUID = 1L; private static final String CALLBACK_PARAM = "callback"; /** * MBean server. */ protected transient MBeanServer mBeanServer; /** * Json Factory to create Json generators for write objects in json format */ protected transient JsonFactory jsonFactory; /** * Initialize this servlet. */ @Override public void init() throws ServletException { // Retrieve the MBean server mBeanServer = ManagementFactory.getPlatformMBeanServer(); jsonFactory = new JsonFactory(); } /** * 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 { JsonGenerator jg = null; String jsonpcb = null; PrintWriter writer = null; try { writer = response.getWriter(); // "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"); } jg = jsonFactory.createGenerator(writer); jg.disable(JsonGenerator.Feature.AUTO_CLOSE_TARGET); jg.useDefaultPrettyPrinter(); jg.writeStartObject(); // query per mbean attribute String getmethod = request.getParameter("get"); if (getmethod != null) { String[] splitStrings = getmethod.split("\\:\\:"); if (splitStrings.length != 2) { jg.writeStringField("result", "ERROR"); jg.writeStringField("message", "query format is not as expected."); jg.flush(); response.setStatus(HttpServletResponse.SC_BAD_REQUEST); return; } listBeans(jg, new ObjectName(splitStrings[0]), splitStrings[1], response); return; } // query per mbean String qry = request.getParameter("qry"); if (qry == null) { qry = "*:*"; } listBeans(jg, new ObjectName(qry), null, response); } finally { if (jg != null) { jg.close(); } if (jsonpcb != null) { writer.write(");"); } if (writer != null) { writer.close(); } } } catch (IOException e) { response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); } catch (MalformedObjectNameException e) { response.setStatus(HttpServletResponse.SC_BAD_REQUEST); } } // --------------------------------------------------------- Private Methods private void listBeans(JsonGenerator jg, ObjectName qry, String attribute, HttpServletResponse response) throws IOException { 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 = ""; Object attributeinfo = null; try { minfo = mBeanServer.getMBeanInfo(oname); code = minfo.getClassName(); String prs = ""; try { if ("org.apache.commons.modeler.BaseModelMBean".equals(code)) { prs = "modelerType"; code = (String) mBeanServer.getAttribute(oname, prs); } if (attribute != null) { prs = attribute; attributeinfo = mBeanServer.getAttribute(oname, prs); } } catch (AttributeNotFoundException e) { // If the modelerType attribute was not found, the class name is used // instead. } catch (MBeanException e) { // The code inside the attribute getter threw an exception so // and fall back on the class name } catch (RuntimeException e) { // For some reason even with an MBeanException available to them // Runtime exceptionscan still find their way through, so treat them // the same as MBeanException } catch (ReflectionException e) { // This happens when the code inside the JMX bean (setter?? from the // java docs) threw an exception, so // class name } } 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 // continue; } catch (ReflectionException e) { // This happens when the code inside the JMX bean threw an exception, so // continue; } jg.writeStartObject(); jg.writeStringField("name", oname.toString()); jg.writeStringField("modelerType", code); if ((attribute != null) && (attributeinfo == null)) { jg.writeStringField("result", "ERROR"); jg.writeStringField("message", "No attribute with name " + attribute + " was found."); jg.writeEndObject(); jg.writeEndArray(); jg.close(); response.setStatus(HttpServletResponse.SC_NOT_FOUND); return; } if (attribute != null) { writeAttribute(jg, attribute, attributeinfo); } else { MBeanAttributeInfo attrs[] = minfo.getAttributes(); for (int i = 0; i < attrs.length; i++) { writeAttribute(jg, oname, attrs[i]); } } 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 if (e.getCause() instanceof UnsupportedOperationException) { } else { } return; } catch (RuntimeErrorException e) { // RuntimeErrorException happens when an unexpected failure occurs in getAttribute // for example https://issues.apache.org/jira/browse/DAEMON-120 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 // skip outputting the attribute 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 return; } catch (ReflectionException e) { //This happens when the code inside the JMX bean (setter?? from the java docs) //threw an exception, so 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 if (value instanceof GaugeValue) { ((GaugeValue) value).serialize(jg); } else { jg.writeString(value.toString()); } } } }