Dynamic, reflective SignalHandler in Java
-
03-10-2019 - |
문제
How do I install signal handling logic iff sun.misc.Signal
is available?
Background First generation of my code, which assumed signal handling availability, looked something like this:
class MyApp {
public static void main(String[] args) {
...
Signal.handle(term_sig, new SignalHandler() {
public void handle(Signal sig) { ... }
});
...
}
}
I believe I understand how to reflectively test for and use signal handlers -- Class.forName("sun.misc.Signal")
, reflectively call Signal.handle
, and so forth.
My impulse was simply to instantiate another anonymous inner class with the dynamically obtained SignalHandler
class, but I think that's just wishful syntax.
해결책
You need to use a Dynamic Proxy to implement the SignalHandler interface. The rest is just basic reflection.
Update
Here's how you do it. Note, I've omitted the try-catch that needs to wrap all of this
Class<?> handlerCl = Class.forName("sun.misc.SignalHandler");
Class<?> signalCl = Class.forName("sun.misc.Signal");
Constructor signalCtor = signalCl.getConstructor(String.class);
Method signalHandle = signalCl.getMethod("handle", signalCl, handlerCl);
// Create a proxy class that implements SignalHandler
Class<?> proxyClass = Proxy.getProxyClass(signalCl.getClassLoader(),
handlerCl);
// This is used by the instance of proxyClass to dispatch method calls
InvocationHandler invHandler = new InvocationHandler()
{
public Object invoke(Object proxy,
Method method, Object[] args) throws Throwable
{
// proxy is the SignalHandler's "this" rederence
// method will be the handle(Signal) method
// args[0] will be an instance of Signal
// If you're using this object for multiple signals, you'll
// you'll need to use the "getName" method to determine which
// signal you have caught.
return null;
}
};
// Get the constructor and create an instance of proxyClass
Constructor<?> proxyCtor = proxyClass.getConstructor(InvocationHandler.class);
Object handler = proxyCtor.newInstance(invHandler);
// Create the signal and call Signal.handle to bind handler to signal
Object signal = signalCtor.newInstance("TERM");
signalHandle.invoke(null, signal, handler);
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