Custom LoggingSystemShutdownHook to initiate/wait for applicationContext.close()

[brenuart]

LoggingApplicationListener registers its own shutdown hook (if so configured) and delegates to the handler provided by the LoggingSystem. The registered hook closes the application context before stopping the logging system.

The implementation should ideally consult the SpringApplication to detect if it is configured to register its own hook or not. Unfortunately this information is not available.

Maybe a cleaner solution is for the SpringApplication to allow for registration of additional hooks that would be invoked after its own. Something like a sequence of hooks, possibly ordered, where the SpringApplication would register its own with higher precedence if so configured. That composite hook would always be registered.

See #4681

[wilkinsona]

@brenuart The Travis build failed for this change. Could you please address the formatting and javadoc problems reported by checkstyle:

/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:124: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:222: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:225:68: Expected @param tag for 'event'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:227: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:231: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:370:96: ')' is preceded with whitespace.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:399: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:400: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:402: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:404: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:405:17: Redundant 'public' modifier.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:408: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:412: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:415: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:427:27: 'if' is not followed by whitespace.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:427:28: '(' is followed by whitespace.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:427:29: Reference to instance variable 'applicationContext' needs "this.".
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:427:55: ')' is preceded with whitespace.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:428:33: Reference to instance variable 'applicationContext' needs "this.".
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:430: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:431: Line matches the illegal pattern 'Trailing whitespace'.
/Users/awilkinson/dev/spring/spring-boot/spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java:434:25: Reference to instance variable 'loggingSystemShutdownHandler' needs "this.".

[wilkinsona]

I think we're in danger of building a house of cards if we pursue the shutdown-hook-based approach. As I said in my comment on 4681, the logging system is now only cleaned up as a result of the root context being closed. This is our preferred approach for shutting down the logging system and should be used in preference to a logging system shutdown hook.