程序启动后启动 Java 代理
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Starting a Java agent after program start
提问by Paul Keeble
Is it possible to insert a javaagent after virtual machine start from within the same VM?
是否可以在虚拟机从同一 VM 内启动后插入 javaagent？
Lets say for example we have an agent in a jar myagent.jar with the appropriate meta data set-up and an agentmain method already implemented. Now the users program calls an API call which should result in the insertion of the agent so that it can redefine the classes.
例如，我们在 jar myagent.jar 中有一个代理，具有适当的元数据设置和已经实现的 agentmain 方法。现在，用户程序调用 API 调用，这将导致插入代理，以便它可以重新定义类。
Can it be done and how?
可以做到吗？如何做到？
回答by Alan Cabrera
https://web.archive.org/web/20141014195801/http://dhruba.name/2010/02/07/creation-dynamic-loading-and-instrumentation-with-javaagents/has a great example of how to write an agent as well as how to start one on the fly.
https://web.archive.org/web/20141014195801/http://dhruba.name/2010/02/07/creation-dynamic-loading-and-instrumentation-with-javaagents/有一个很好的例子来说明如何编写代理以及如何即时启动代理。
回答by 11101101b
Yes, you just have to pass the JVM process ID to the VirtualMachine.attach(String pid)method, and load the agent jar. The VirtualMachineclass is available in the JDK_HOME/lib/tools.jar file. Here's an example of how I activate an agent at runtime:
是的，您只需将 JVM 进程 ID 传递给该VirtualMachine.attach(String pid)方法，然后加载代理 jar。该VirtualMachine班在JDK_HOME / lib目录/文件的tools.jar可用。这是我如何在运行时激活代理的示例：
public static void attachGivenAgentToThisVM(String pathToAgentJar) {
try {
String nameOfRunningVM = ManagementFactory.getRuntimeMXBean().getName();
String pid = nameOfRunningVM.substring(0, nameOfRunningVM.indexOf('@'));
VirtualMachine vm = VirtualMachine.attach(pid);
vm.loadAgent(pathToAgentJar, "");
vm.detach();
} catch (Exception e) {
e.printStackTrace();
}
}
回答by HerdplattenToni
You should be able to do it in Java 6, see the package documentationchapter "Starting Agents After VM Startup"
您应该可以在 Java 6 中执行此操作，请参阅包文档章节“在 VM 启动后启动代理”
edit: Maybe it was possible in Java 5 already and just the javadocs didn't mention it that explicitly
编辑：也许在 Java 5 中已经有可能了，只是 javadocs 没有明确提到它
