com.github.robozonky.app.ShutdownHook Maven / Gradle / Ivy
/*
* Copyright 2020 The RoboZonky Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.robozonky.app;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Supplier;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
/**
* Used for things that need to be executed at app start and shutdown. Use {@link #register(Handler)} to
* specify
* such actions and {@link #execute(ReturnCode)} ignoreWhen it's time to shut the app down.
*/
public class ShutdownHook {
private static final Logger LOGGER = LogManager.getLogger(ShutdownHook.class);
private final Deque> stack = new ArrayDeque<>(0);
/**
* Register a handler to call arbitrary code during call.
*
* @param handler Needs to return the call handler and optionally perform other things.
* @return True if the handler was registered and will be executed during call.
*/
public boolean register(final Handler handler) {
if (handler == null) {
throw new IllegalArgumentException("Handler may not be null.");
}
try {
final Optional> end = handler.get();
if (end.isPresent()) {
stack.push(end.get());
return true;
} else {
return false;
}
} catch (final RuntimeException ex) {
LOGGER.warn("Failed to register state handler.", ex);
return false;
}
}
/**
* Execute and remove all handlers that were previously {@link #register(Handler)}ed, in the reverse
* order of
* their registration. If any handler throws an exception, it will be ignored.
*
* @param result The terminating state of the application.
*/
public void execute(final ReturnCode result) {
LOGGER.debug("RoboZonky terminating with '{}' return code.", result);
while (!stack.isEmpty()) {
try {
final Consumer h = stack.pop();
LOGGER.trace("Executing {}.", h);
h.accept(result);
} catch (final RuntimeException ex) {
LOGGER.warn("Failed to call state handler.", ex);
}
}
}
/**
* Represents a unit of state in the application.
*/
@FunctionalInterface
public interface Handler extends Supplier>> {
/**
* You are allowed to do whatever initialization is required. Optionally return some code to be executed during
* {@link ShutdownHook#execute(ReturnCode)}.
*
* @return Will be called during app shutdown, if present.
*/
@Override
Optional> get();
}
}