Closure Hooks for Java (Shutdown hook)

Runtime.getruntime (). Addshutdownhook (Shutdownhook);

The implication of this method is that the method means adding a closed hook to the JVM, and when the JVM shuts down, it executes all the hooks that have been set in the system via the method Addshutdownhook, and the JVM shuts down when the system finishes executing the hooks. So these hooks can be used for memory cleanup, object destruction and so on when the JVM shuts down.

Use

1 The application exits gracefully, executes specific business logic when exiting, or shuts down resources.

2 Abnormal exit of virtual machine, such as user press CTRL + C, outofmemory down, operating system shutdown, etc. Perform the necessary salvage measures at the time of exit.

Example:

public class Jvmhook {

 public static void Start () {
  system.out.println ("The JVM is Started ");
  runtime.getruntime (). Addshutdownhook (New Thread () {
   public void Run () {
    try{
     //do something
      System.out.println ("The JVM Hook is execute");
    }catch (Exception e) {
     e.printstacktrace ();
    }
   }
  });
 }
 
 public static void Main (string[] args) {
  start ();
  
  system.out.println ("The application is doing something");
  
  
  
  try {
   thread.sleep (+);
  } catch (Interruptedexception e) {
   e.printstacktrace ();
  }
 }
}

Output Result:

The JVM is started
The application is doing something
The JVM Hook is execute

The last one is output after three seconds when the JVM shuts down.

examples given for the 2nd use:Package Com.java.seven;Public class Jvmhook {public static void Start () {
System.out.println ("The JVM is started");
Runtime.getruntime (). Addshutdownhook (New Thread () {
public void Run () {
try{
Do something
System.out.println ("The JVM Hook is execute");
}catch (Exception e) {
E.printstacktrace ();
}
}
});
}

public static void Main (string[] args) {
Start ();

System.out.println ("The application is doing something");

Byte[] B = new byte[500*1024*1024];

System.out.println ("The application continues to do something");

try {
Thread.Sleep (3000);
} catch (Interruptedexception e) {
E.printstacktrace ();
}
}
}

Output Result:

The JVM is started
The application is doing something
Exception in thread "main" Java.lang.OutOfMemoryError:Java heap space
At Com.java.seven.JVMHook.main (jvmhook.java:24)
The JVM Hook is execute

There are some remedial measures that can be made when outofmemoryerror.

Recommendation: The same JVM is best to use only one closure hook, instead of each service using a different closure hook, using multiple close hooks may appear the current hook to rely on the service may have been closed by another closure hook. To avoid this situation, it is recommended that the shutdown operation be executed serially in a single thread, thus avoiding race conditions or deadlocks between shutdown operations.

Closure Hooks for Java (Shutdown hook)