Chapter 4 Tracing Mechanism

This chapter explains how to use the tracing mechanism to help you trace or debug the Java Dynamic Management Kit (DMK) API. The tracing mechanism uses the notification mechanism to distribute the trace and debug information, giving you internal runtime information. You can specify the information type and level of trace and debug information you want to receive. To receive trace and debug information you must add a notification listener to the class com.sun.jdmk.TraceManager.

You control the tracing by defining the trace properties specific to the Java DMK. Three factors affect tracing:

• Various components that send trace messages

• Level of detail

• Output destination

The com.sun.jdmk.trace.Trace class is used to emit trace messages. All the classes of the Java DMK use this Trace class for sending traces. You can use the Trace class in your own code for producing debug traces for your own classes.

The com.sun.jdmk.TraceManager class provides methods for receiving trace and debug messages. Options provided by the TraceManager class are described in the following sections:

• Receiving Trace and Debug Information

• Specifying the Type of Trace and Debug Information

• Specifying the Level of Trace and Debug Information

Receiving Trace and Debug Information

The com.sun.jdmk.TraceManager class uses the notification mechanism to distribute the information. You must add a notification listener to receive information (see example Example 4–1). There are two ways to receive trace information:

• Adding a notification listener with a filter in the code. It is possible to have more than one notification listener but with different filters. With TraceFilter, you can specify the type and level of information you want to receive. See Example 4–3 and Example 4–2.

• Specifying system properties in the command to start the Java interpreter when you run a class. In this case, the code of the class must include a call to the TraceManager method. When the TraceManager method is called, all the previously enabled trace and debug information are disabled. Only the properties currently defined when the method is called are enabled.

Example 4–1 Creating a Notification Listener

// Create a listener and save all info to the file /tmp/trace 
TraceListener listener = new TraceListener("/tmp/trace"); 

Example 4–2 Creating a Trace Filter

// create a trace filter with LEVEL_DEBUG and INFO_ALL/
TraceFilter filter = new TraceFilter(Trace.LEVEL_DEBUG, Trace.INFO_ALL);

Example 4–3 Adding the Notification Listener to the class

// add the listener to the class Trace/
TraceManager.addNotificationListener(listener, filter, null);

Specifying the Type of Trace and Debug Information

It is possible to specify the type of trace and debug information you want to receive. The following types are specified:

• INFO_MBEANSERVER: information about the MBean server

• INFO_MLET: information from an m-let service

• INFO_MONITOR: information from a monitor

• INFO_TIMER: information from a timer

• INFO_ADAPTOR_CONNECTOR: information concerning all adaptors and connectors

• INFO_ADAPTOR_HTML: information from an HTML adaptor

• INFO_CONNECTOR_RMI: information from a RMI connector

• INFO_CONNECTOR_HTTP: information from HTTP connectors

• INFO_CONNECTOR_HTTPS: information from HTTPS connectors

• INFO_ADAPTOR_SNMP: information from an SNMP adaptor

• INFO_DISCOVERY: information from a discovery service

• INFO_SNMP: information from an SNMP manager service

• INFO_NOTIFICATION: information from notification mechanism

• INFO_HEARTBEAT: information from heartbeat mechanism

• INFO_RELATION: information from relation service

• INFO_MODELMBEAN: information from the model MBean components

• INFO_MISC: information sent from any other classes

• INFO_ALL: information from all classes

The preceding information is held by the TraceTags class

Specifying the Level of Trace and Debug Information

The level of detail controls the number of messages you receive. The trace level is the default that gives information about the actions of the MBean server and other components. The debug level includes all the trace information providing information to help diagnose Java DMK implementation. If this level is specified, the information of LEVEL_TRACE is sent too. It is possible to specify the level of trace or debug information you want to receive. Two levels of information are specified in the TraceTags class:

LEVEL_TRACE

Provides information to help a developer when programming

LEVEL_DEBUG

Provides information to help diagnose Java DMK implementation

If you choose the second option, you will automatically receive all trace information as well as debug information. By default, the level is set to LEVEL_TRACE.