如何为已经运行的实例更改Java类的代码？

Question

I wish to dynamically add and remove instrumentation code to a Java class file several times without restarting the Java JVM. Is this possible?

Answer 1

I suggest you look at the java.lang.instrument package , especially the ClassFileTransformer .

Here is a good article: Instrumentation: Modify Applications with Java 5 Class File Transformations

For actual bytecode generation, I suggest you have a look at libraries such as BCEL or ASM .

The JRebel framework may also interest you. It can change implementation of method bodies, add / remove methods and constructors, add/remove fields, add/remove classes etc, all in runtime.

Answer 2

您可以使用辅助类（策略设计模式），它可以在运行时交换为另一个。

Answer 3

You can use Jrebel for hot deployment. It will allow you to change the code without server restart.

Answer 4

You also might want to look at ByteMan from JBoss. It uses the same Java agent mechanism and specifically supports installing and uninstalling your modification scripts, see the tutorial . What follows is an abridged version of the tutorial:

For example lets say we have some running Java Process:

$ jps
15295 Jps
4884 main

We can then install ByteMan into the running process:

$ bminstall.sh 4884

You could then create a ByteMan script:

$ youreditor thread.btm
RULE trace thread start
CLASS java.lang.Thread
METHOD start()
IF true
DO traceln("*** start for thread: "+ $0.getName())
ENDRULE

You can then install a ByeMan script with:

$ bmsubmit.sh -l thread.btm

To remove:

$ bmsubmit.sh -u thread.btm

To list what is currently running just issue it without any arguments:

$ bmsubmit.sh

If you are running on windows replace the .sh in each command with .bat.