org.apache.hadoop.jmx

Class JMXJsonServlet

java.lang.Object

javax.servlet.GenericServlet

javax.servlet.http.HttpServlet

org.apache.hadoop.jmx.JMXJsonServlet

All Implemented Interfaces:

Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

public class JMXJsonServlet
extends javax.servlet.http.HttpServlet

Provides Read only web access to JMX.

This servlet generally will be placed under the /jmx URL for each HttpServer. It provides read only access to JMX metrics. The optional qry parameter may be used to query only a subset of the JMX Beans. This query functionality is provided through the MBeanServer.queryNames(ObjectName, javax.management.QueryExp) method.

For example http://.../jmx?qry=Hadoop:* will return all hadoop metrics exposed through JMX.

The optional get parameter is used to query an specific attribute of a JMX bean. The format of the URL is http://.../jmx?get=MXBeanName::AttributeName

For example http://../jmx?get=Hadoop:service=NameNode,name=NameNodeInfo::ClusterId will return the cluster id of the namenode mxbean.

If the qry or the get parameter is not formatted correctly then a 400 BAD REQUEST http response code will be returned.

If a resouce such as a mbean or attribute can not be found, a 404 SC_NOT_FOUND http response code will be returned.

The return format is JSON and in the form

  {
    "beans" : [
      {
        "name":"bean-name"
        ...
      }
    ]
  }
  

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 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 TabularData then it will be converted to an array of the 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.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected MBeanServer	mBeanServer MBean server.

Constructor Summary

Constructors

Constructor and Description
JMXJsonServlet()

Method Summary

Methods

Modifier and Type	Method and Description
void	doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) Process a GET request for the specified resource.
void	init() Initialize this servlet.

Methods inherited from class javax.servlet.http.HttpServlet

doDelete, doHead, doOptions, doPost, doPut, doTrace, getLastModified, service, service

Methods inherited from class javax.servlet.GenericServlet

destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

mBeanServer

protected transient MBeanServer mBeanServer

MBean server.

Constructor Detail

JMXJsonServlet

public JMXJsonServlet()

Method Detail

init

public void init()
          throws javax.servlet.ServletException

Initialize this servlet.

Overrides:

init in class javax.servlet.GenericServlet

Throws:

javax.servlet.ServletException

doGet

public void doGet(javax.servlet.http.HttpServletRequest request,
         javax.servlet.http.HttpServletResponse response)

Process a GET request for the specified resource.

Overrides:

doGet in class javax.servlet.http.HttpServlet

Parameters:

request - The servlet request we are processing

response - The servlet response we are creating