June 2002
Intermediate to advanced
312 pages
9h 18m
English
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Chapter 8. Dynamic Loading
In this chapter, we will discuss a facility provided by JMX that allows MBeans to be loaded into an agent dynamically. This facility, called the M-Let (short for management applet) service, is the first agent-level service we have discussed so far. There are two major sections in this chapter. The first section is an overview of the M-Let service, including the various facets of it that make it work. The second section deals with the details of the M-Let service and provides examples of code that executes in the JMX agent that uses the M-Let service.
Overview
In this section, we will look at the M-Let service, whose purpose is
to provide an agent with a means to load MBeans from a Universal
Resource Locator (URL). There are two ways that an agent can use the
M-Let service to accomplish this. First, the agent can specify an
M-Let file to the M-Let service, which uses the
contents of this file to load the MBeans. The M-Let file is an
XML-like text file that contains various tags that describe the
MBeans to be loaded. The second method of loading MBeans is to use
the M-Let service itself to load the MBeans without the use of an
M-Let file. The M-Let service extends
URLClassLoader from the
java.net package and is thus capable of fetching
bytecode from any valid URL into the JVM in which the agent is
running.
The M-Let Service
In the RI, the M-Let
service is implemented in a class called MLet,
which implements an interface called MLetMBean (so it is instrumented ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.