| JavaTM 2 Platform Std. Ed. v1.5.0
Package java.lang.instrument
Provides services that allow Java programming language agents to instrument programs running on the JVM.
See:
Description
|
Interface Summary |
| ClassFileTransformer |
An agent provides an implementation of this interface in order
to transform class files. |
| Instrumentation |
This class provides services needed to instrument Java
programming language code. |
|
Class Summary |
| ClassDefinition |
This class serves as a parameter block to the Instrumentation.redefineClasses method. |
Package java.lang.instrument Description
Provides services that allow Java programming language agents to instrument programs running on the JVM.
The mechanism for instrumentation is modification of the byte-codes of methods.
Package Specification
An agent is launched by indicating the agent class and
its agent options when the JVM is launched.
The agent class must implement a public static premain method
similar in principle to the main application entry point:
public static void
premain(String agentArgs, Instrumentation inst);
After the JVM is initialized, each premain method will be called in the order
the agents were specified,
then the real application main method will be called.
Each premain method must return in order for the startup sequence to proceed.
The agent class will be loaded by the same classloader
which loads the class containing the application main method.
The premain methods will be run under the same security and classloader
rules as the application main method.
There are no modeling restrictions on what the agent premain method may do.
Anything application main can do, including spawning threads, is legal from premain.
Each agent is passed its agent options via the agentArgs parameter.
The agent options are passed as a single string,
any additional parsing should be performed by the agent itself.
If the agent cannot be resolved
(for example, because the agent class cannot be loaded,
or because the agent class does not have a conformant premain method), the JVM will abort.
If a premain method throws an uncaught exception, the JVM will abort.
Command-Line Interface
On JVMs with a command-line interface, agents are specified by adding this switch to the JVM command-line:
-javaagent:jarpath[=options]
jarpath is the path to the agent JAR file.
options is the agent options.
This switch may be used multiple times on the same command line,
thus creating multiple agents.
More than one agent may use the same jarpath.
An agent JAR file must conform to the JAR file specification.
The following manifest attributes are defined for an agent JAR file:
Premain-Class-
The agent class. That is,
the class containing the
premain method.
This attribute is required, if it is not present the
JVM will abort.
Note: this is a class name, not a file name or path.
Boot-Class-Path-
A list of paths to be searched by the bootstrap class
loader. Paths represent directories or libraries
(commonly referred to as jar or zip libraries on
many platforms).
These paths are searched by the
bootstrap class loader after the platform specific
mechanisms of locating a class have failed.
Paths are searched in the order listed.
Paths in the list are separated by one or more spaces.
A path takes the syntax of the path component of a
hierarchical URI. The path is
absolute if it begins with a slash character ('/'),
otherwise it is relative. A relative path is resolved
against the absolute path of the agent JAR file.
Malformed and non-existent paths are ignored.
This attribute is optional.
Can-Redefine-Classes-
Boolean (
true or false, case irrelevant).
Is the ability to redefine classes
needed by this agent.
Values other than true are considered false.
This attribute is optional, the default is false.
The agent JAR file is appended to the class path.
Related Documentation
For tool documentation, please see:
- Since:
- JDK1.5
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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