How to stop java application

How to stop java application

Basically every java application is terminated when end of main method is reached or when all running threads run out of code. Find more information about stopping threads (here).

It is possible to force java application to terminate immediately with simple method call:

This method can be called anytime from within the code (eg. when user clicks ‘Quit’ button or in case of fatal errors). JVM is terminated immediately. As a consequence all data in application is lost — objects are gone, opened connections might hang in some weird state.

On Linux systems java application can be terminated from console window in the same way as any other process — kill the process. Before executing kill command you need to know the process id (PID) of your java application. This can be done in many ways. Example (PID is colored with red):

> ps -ef | grep java
501 346 242 0 0:00.04 ttys000 0:00.13 /usr/bin/java -jar javaShutdownHook.jar
501 348 254 0 0:00.00 ttys001 0:00.00 grep java

Process id can also be viewed by a tool jps which is part of JDK instalation (not JRE).

> jps -ml
346 javaShutdownHook.jar
349 sun.tools.jps.Jps -ml

Once you know the process id of process you want to terminate, simply execute:

But how to regularly stop an application without any ‘Quit’ button? Services for example. Usually they don’t have any GUI and the applications were meant to run forever in the background.

To stop an application in a regular manner you need to add ‘a shutdown hook’ to your java application. When kill command is executed, a special signal SIGTERM is sent to java process. The signal is intercepted by Runtime class (java.lang) which is the bond with the underlaying operating system, and consequently start the shutdown procedure.

A shutdown hook is a simple Thread object. The developer should implement the shutdown procedure within the run() method. Pass the Thread to the Runtime object by calling addShutdownHook(Thread t) method. When SIGTERM signal is received, Runtime class will start the thread.

Let’s try shutdown hook in action. This is the scenario: make a simple loop with counter which is increased every second (imagine this is a service). Then make a thread which will set the running flag to false and therefore exit the counter loop — then the application will reach end of main method in regular way. At the beginning of application set the Thread as a shutdown hook.

Remember: don’t call start() method to run the Thread — Runtime class will do it!

Test class with main method:

public static boolean running = true;

public static void main(String[] args)

System.out.println(«+++ JavaStopTest started +++»);

int i = 0;
while (running) System.out.println(«count — JavaStopTest ended —«);
>

public class MyShutdownHook extends Thread

@Override
public void run() System.out.println(«=== my shutdown hook activated»);

// stop running threads
// store data to DB
// close connection to DB
// disconnect.
// release other resources.

Build and run the code (from console) — you should see counter running. Open another console window, search for the PID of java process and kill the process (you have 100 seconds). Download already built jar (here).

Running example in two consoles:

CONSOLE 1: CONSOLE 2: # start application > java -jar javaShutdownHook.jar +++ StopTest started +++ count=0 count=1 count=2 count=3 . # get PID > jps -ml 7096 javaShutdownHook.jar # stop application > kill 7096 . count=51 count=52 === shutdown hook activated # application is stopped

Overriding shutdown hook

A shutdown hook is not executed if java process is terminated with:

Kill level 9 sends more effective termination signal (SIGKILL), which terminates the application immediately without running the shutdown hook.

The same happens when the system is going to reboot or shutdown. First a SIGTERM signal is sent to all processes. Then the system waits for applications to terminate regularly. If applications fail to terminate after some time, SIGKILL signal is sent to force quit an application.

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How to stop java application

Basically every java application is terminated when end of main method is reached or when all running threads run out of code. Find more information about stopping threads (here).

It is possible to force java application to terminate immediately with simple method call:

This method can be called anytime from within the code (eg. when user clicks ‘Quit’ button or in case of fatal errors). JVM is terminated immediately. As a consequence all data in application is lost — objects are gone, opened connections might hang in some weird state.

On Linux systems java application can be terminated from console window in the same way as any other process — kill the process. Before executing kill command you need to know the process id (PID) of your java application. This can be done in many ways. Example (PID is colored with red):

> ps -ef | grep java
501 346 242 0 0:00.04 ttys000 0:00.13 /usr/bin/java -jar javaShutdownHook.jar
501 348 254 0 0:00.00 ttys001 0:00.00 grep java

Process id can also be viewed by a tool jps which is part of JDK instalation (not JRE).

> jps -ml
346 javaShutdownHook.jar
349 sun.tools.jps.Jps -ml

Once you know the process id of process you want to terminate, simply execute:

But how to regularly stop an application without any ‘Quit’ button? Services for example. Usually they don’t have any GUI and the applications were meant to run forever in the background.

To stop an application in a regular manner you need to add ‘a shutdown hook’ to your java application. When kill command is executed, a special signal SIGTERM is sent to java process. The signal is intercepted by Runtime class (java.lang) which is the bond with the underlaying operating system, and consequently start the shutdown procedure.

A shutdown hook is a simple Thread object. The developer should implement the shutdown procedure within the run() method. Pass the Thread to the Runtime object by calling addShutdownHook(Thread t) method. When SIGTERM signal is received, Runtime class will start the thread.

Let’s try shutdown hook in action. This is the scenario: make a simple loop with counter which is increased every second (imagine this is a service). Then make a thread which will set the running flag to false and therefore exit the counter loop — then the application will reach end of main method in regular way. At the beginning of application set the Thread as a shutdown hook.

Remember: don’t call start() method to run the Thread — Runtime class will do it!

Test class with main method:

public static boolean running = true;

public static void main(String[] args)

System.out.println(«+++ JavaStopTest started +++»);

int i = 0;
while (running) System.out.println(«count — JavaStopTest ended —«);
>

public class MyShutdownHook extends Thread

@Override
public void run() System.out.println(«=== my shutdown hook activated»);

// stop running threads
// store data to DB
// close connection to DB
// disconnect.
// release other resources.

Build and run the code (from console) — you should see counter running. Open another console window, search for the PID of java process and kill the process (you have 100 seconds). Download already built jar (here).

Running example in two consoles:

CONSOLE 1: CONSOLE 2: # start application > java -jar javaShutdownHook.jar +++ StopTest started +++ count=0 count=1 count=2 count=3 . # get PID > jps -ml 7096 javaShutdownHook.jar # stop application > kill 7096 . count=51 count=52 === shutdown hook activated # application is stopped

Overriding shutdown hook

A shutdown hook is not executed if java process is terminated with:

Kill level 9 sends more effective termination signal (SIGKILL), which terminates the application immediately without running the shutdown hook.

The same happens when the system is going to reboot or shutdown. First a SIGTERM signal is sent to all processes. Then the system waits for applications to terminate regularly. If applications fail to terminate after some time, SIGKILL signal is sent to force quit an application.

Recently seen.

Most used

Hot stuff

By the way.

You can always use traditional HTML tags such as p, h1, h2, div, etc.

Raspberry Pi projects

Controll LED
DHT-11
Photoresistor

Источник

End a Java Program

1. System.exit() to Terminate a Java Program
2. return to Exit From a Function in Java

This article shows all the best ways that we can use to end a running program in Java. We will go through a few examples to understand the situation and the easiest way to handle it.

System.exit() to Terminate a Java Program

To end a Java program, we can use the exit() method of the System class. It is the most popular way to end a program in Java. System.exit() terminates the Java Virtual Machine(JVM) that exits the current program that we are running.

Below is a simple example that uses the System.exit() method. Notice that it takes an integer, which is the status code. We pass 0 to the exit() function, which indicates that the termination happens successfully without any error. A non-zero status like 1 and -1 tells the compiler to terminate the program with some error or message.

You can see that the output only prints Statement 1 in the below example because the program exits after its execution and Statement 2 was never able to be executed.

public class Main   public static void main(String[] args)   System.out.println("Statement 1");  System.exit(0);  System.out.println("Statement 2");  > > 

Statement 1  Process finished with exit code 0 

return to Exit From a Function in Java

Sometimes we might have to terminate a function instead of the Java Virtual Machine, and that is when the return keyword of Java comes into play. This keyword is very useful when we are using functions in our program.

In formal language, return can be used to complete the method execution. It means that we can use this way to exit our function.

The following example shows how we can return a String from the function. If the value is false , it will return Statement 2 and then ignore Statement 3 as the execution of this method has been completed.

 public class Main   public static void main(String[] args)   boolean value = false;   String getValueFromFunc = func(value);  System.out.println(getValueFromFunc);  >   public static String func(boolean value)  if(value)  System.out.println("Statement 1");  >else  return "Statement 2";  >  return "Statement 3";  >  > 

But what if the value is true? Let’s find out in the next example.

The output prints Statement 1 as well as Statement3, which was ignored in the previous example. It happened because the statement block of if condition has println instead of a return .

public class Main   public static void main(String[] args)   boolean value = true;   String getValueFromFunc = func(value);  System.out.println(getValueFromFunc);  >   public static String func(boolean value)  if(value)  System.out.println("Statement 1");  >else  return "Statement 2";  >  return "Statement 3";  >  > 

Rupam Saini is an android developer, who also works sometimes as a web developer., He likes to read books and write about various things.

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