Package 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

Direct Known Subclasses:

JMXJsonServletNaNFiltered

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	Description
protected com.fasterxml.jackson.core.JsonFactory	jsonFactory	Json Factory to create Json generators for write objects in json format
protected MBeanServer	mBeanServer	MBean server.

Constructor Summary

Constructors

Constructor	Description
JMXJsonServlet()

Method Summary

Modifier and Type	Method	Description
void	doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)	Process a GET request for the specified resource.
protected void	doTrace(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)	Disable TRACE method to avoid TRACE vulnerability.
protected boolean	extraCheck(Object value)	In case you need to modify the logic, how java objects transforms to json, you can overwrite this method to return true in case special handling
protected void	extraWrite(Object value, String attName, com.fasterxml.jackson.core.JsonGenerator jg)
void	init()	Initialize this servlet.
protected boolean	isInstrumentationAccessAllowed(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)

Methods inherited from class javax.servlet.http.HttpServlet

doDelete, doHead, doOptions, doPost, doPut, 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 Details

mBeanServer

protected transient MBeanServer mBeanServer

MBean server.

jsonFactory

protected transient com.fasterxml.jackson.core.JsonFactory jsonFactory

Json Factory to create Json generators for write objects in json format

Constructor Details

JMXJsonServlet

public JMXJsonServlet()

Method Details

init

public void init()
          throws javax.servlet.ServletException

Initialize this servlet.

Overrides:

init in class javax.servlet.GenericServlet

Throws:

javax.servlet.ServletException

isInstrumentationAccessAllowed

protected boolean isInstrumentationAccessAllowed(javax.servlet.http.HttpServletRequest request,
 javax.servlet.http.HttpServletResponse response)
                                          throws IOException

Throws:

IOException

doTrace

protected void doTrace(javax.servlet.http.HttpServletRequest req,
 javax.servlet.http.HttpServletResponse resp)
                throws javax.servlet.ServletException,
IOException

Disable TRACE method to avoid TRACE vulnerability.

Overrides:

doTrace in class javax.servlet.http.HttpServlet

Throws:

javax.servlet.ServletException

IOException

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

extraCheck

protected boolean extraCheck(Object value)

In case you need to modify the logic, how java objects transforms to json, you can overwrite this method to return true in case special handling

Parameters:

value - the object what should be judged

Returns:

true, if it needs special transformation

extraWrite

protected void extraWrite(Object value,
 String attName,
 com.fasterxml.jackson.core.JsonGenerator jg)
                   throws IOException

Throws:

IOException