问题描述
是否可以在 JVM 已经加载(运行)之后更改/修改/添加 VM 参数?如果是这样，我该怎么做?
Is it possible to change/modify/adding VM parameters after the JVM is already loaded (running)? If so, how can I do it?
推荐答案
对于您通过命令行上的 -D 标志设置的属性，您需要 System.setProperty.例如:
For properties you'd set via the -D flag on the command line, you want System.setProperty. For example:
System.setProperty("propname", "hello world");
// ... later ...
String value = System.getProperty("propname");
更新:
您不能动态启用调试，但您可以在启动时启用调试但稍后附加调试器.通过以下操作，您可以监听端口 12345 并立即启动程序运行(通过 suspend=n).然后，您可以在需要时附加调试器，分离调试器，稍后再附加，等等.
You can't enable debugging dynamically, but you can enable debugging at startup but attach a debugger later. With the following, you can listen on port 12345 and start your program running right away (via suspend=n). Then you can attach a debugger if/when you need to, detach the debugger, attach again later, etc.
-Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=12345
当然，即使没有附加调试器，这也会影响性能，因此它只能在开发/测试代码中运行良好，而不是在生产环境中运行.为此，您需要记录，例如log4j.
Of course, this hurts performance even when the debugger isn't attached, so it only works well in dev/test code, not production. For that, you want logging, e.g. log4j.
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