How can I restart a Java application

Question

How can I restart a Java AWT application  I have a button to which I have attached an event handler  What code should I use to restart the application   I want to do the same thing that Application Restart   do in a C  application

User · Answer

I was researching the subject myself when came across this question.

Regardless of the fact that the answer is already accepted, I would still like to offer an alternative approach for completeness. Specifically, Apache Ant served as a very flexible solution.

Basically, everything boils down to an Ant script file with a single Java execution task (refer here and here) invoked from a Java code (see here). This Java code, which can be a method launch, could be a part of the application that needs to be restarted. The application needs to have a dependency on the Apache Ant library (jar).

Whenever application needs to be restarted, it should call method launch and exit the VM. The Ant java task should have options fork and spawn set to true.

Here is an example of an Ant script:

<project name="applaucher" default="launch" basedir=".">
<target name="launch">
    <java classname="package.MasinClass" fork="true" spawn="true">
        <jvmarg value="-splash:splash.jpg"/>
        <jvmarg value="-D other VM params"/>
        <classpath>
            <pathelement location="lib-1.jar" />
            ...
            <pathelement location="lib-n.jar" />
        </classpath>
    </java>
</target>
</project>

The code for the launch method may look something like this:

public final void launch(final String antScriptFile) {
 /* configure Ant and execute the task */
   final File buildFile = new File(antScriptFile);
   final Project p = new Project();
   p.setUserProperty("ant.file", buildFile.getAbsolutePath());

   final DefaultLogger consoleLogger = new DefaultLogger();
   consoleLogger.setErrorPrintStream(System.err);
   consoleLogger.setOutputPrintStream(System.out);
   consoleLogger.setMessageOutputLevel(Project.MSG_INFO);
   p.addBuildListener(consoleLogger);

   try {
       p.fireBuildStarted();
       p.init();
       final ProjectHelper helper = ProjectHelper.getProjectHelper();
       p.addReference("ant.projectHelper", helper);
       helper.parse(p, buildFile);
       p.executeTarget(p.getDefaultTarget());
       p.fireBuildFinished(null);
   } catch (final BuildException e) {
       p.fireBuildFinished(e);
   }

   /* exit the current VM */
   System.exit(0);

}

A very convenient thing here is that the same script is used for initial application start up as well as for restarts.

User · Answer

Basically  you can t  At least not in a reliable way  However  you shouldn t need to  The can t part To restart a Java program  you need to restart the JVM  To restart the JVM you need to  Locate the java launcher that was used  You may try with System getProperty  quot java home quot   but there s no guarantee that this will actually point to the launcher that was used to launch your application   The value returned may not point to the JRE used to launch the application or it could have been overridden by -Djava home    You would presumably want to honor the original memory settings etc  -Xmx  -Xms       so you need to figure out which settings where used to start the first JVM  You could try using ManagementFactory getRuntimeMXBean   getInputArguments   but there s no guarantee that this will reflect the settings used  This is even spelled out in the documentation of that method   Typically  not all command-line options to the  java  command are passed to the Java virtual machine  Thus  the returned input arguments may not include all command-line options    If your program reads input from Standard in the original stdin will be lost in the restart   Lots of these tricks and hacks will fail in the presence of a SecurityManager    The shouldn t need part I recommend you to design your application so that it is easy to clean every thing up and after that create a new instance of your  quot main quot  class  Many applications are designed to do nothing but create an instance in the main-method  public class MainClass               public static void main String   args            new MainClass   launch                     By using this pattern  it should be easy enough to do something like  public class MainClass               public static void main String   args            boolean restart          do               restart   new MainClass   launch              while  restart                    and let launch   return true if and only if the application was shut down in a way that it needs to be restarted

User · Answer

Windows  public void restartApp            This launches a new instance of application dirctly          remember to add some sleep to the start of the cmd file to make sure current instance is        completely terminated  otherwise 2 instances of the application can overlap causing strange        things        new ProcessBuilder  cmd    c start  min c  path to script that launches my application cmd   amp  exit   start        System exit 0        min to start script in minimized window    amp  exit to close cmd window after finish  a sample cmd script could be   echo off rem add some sleep  e g  10 seconds  to allow the preceding application instance to release any open resources  like ports  and exit gracefully  otherwise the new instance could fail to start sleep 10    set path C  someFolder application lib libs  path  java -jar application jar   sleep 10 sleep for 10 seconds

User · Answer

Although this question is old and answered  I ve stumbled across a problem with some of the solutions and decided to add my suggestion into the mix   The problem with some of the solutions is that they build a single command string  This creates issues when some parameters contain spaces  especially java home    For example  on windows  the line  final String javaBin   System getProperty  java home     File separator    bin    File separator    java     Might return something like this C  Program Files Java jre7 bin java  This string has to be wrapped in quotes or escaped due to the space in Program Files  Not a huge problem  but somewhat annoying and error prone  especially in cross platform applications   Therefore my solution builds the command as an array of commands   public static void restart String   args             ArrayList lt String gt  commands   new ArrayList lt String gt  4   jvmArgs size     args length           List lt String gt  jvmArgs   ManagementFactory getRuntimeMXBean   getInputArguments                Java         commands add System getProperty  java home     File separator    bin    File separator    java                Jvm arguments         for  String jvmArg   jvmArgs                commands add jvmArg                         Classpath         commands add  -cp            commands add ManagementFactory getRuntimeMXBean   getClassPath                 Class to be executed         commands add BGAgent class getName                 Command line arguments         for  String arg   args                commands add arg                      File workingDir   null     Null working dir means that the child uses the same working directory          String   env   null     Null env means that the child uses the same environment          String   commandArray   new String commands size             commandArray   commands toArray commandArray            try               Runtime getRuntime   exec commandArray  env  workingDir               System exit 0             catch  IOException e                e printStackTrace

User · Answer

System err println  Someone is Restarting me       setVisible false   try       Thread sleep 600     catch  InterruptedException e1        e1 printStackTrace      setVisible true     I guess you don t really want to stop the application  but to  Restart  it   For that  you could use this and add your  Reset  before the sleep and after the invisible window

User · Answer

Of course it is possible to restart a Java application   The following method shows a way to restart a Java application   public void restartApplication       final String javaBin   System getProperty  java home     File separator    bin    File separator    java     final File currentJar   new File MyClassInTheJar class getProtectionDomain   getCodeSource   getLocation   toURI           is it a jar file       if  currentJar getName   endsWith   jar        return        Build command  java -jar application jar      final ArrayList lt String gt  command   new ArrayList lt String gt       command add javaBin     command add  -jar      command add currentJar getPath        final ProcessBuilder builder   new ProcessBuilder command     builder start      System exit 0       Basically it does the following    Find the java executable  I used the java binary here  but that depends on your requirements  Find the application  a jar in my case  using the MyClassInTheJar class to find the jar location itself  Build a command to restart the jar  using the java binary in this case  Execute it   and thus terminating the current application and starting it again

User · Answer

Similar to Yoda s  improved  answer  but with further improvements  both functional  readability  and testability   It s now safe to run  and restarts for as as many times as the amount of program arguments given    No accumulation of JAVA TOOL OPTIONS options  Automatically finds main class  Inherits current stdout stderr      public static void main String   args  throws Exception       if  args length    0          return      else         args   Arrays copyOf args  args length - 1        List lt String gt  command   new ArrayList lt  gt  32       appendJavaExecutable command       appendVMArgs command       appendClassPath command       appendEntryPoint command       appendArgs command  args        System out println command       try           new ProcessBuilder command  inheritIO   start          catch  IOException ex            ex printStackTrace             private static void appendJavaExecutable List lt String gt  cmd        cmd add System getProperty  java home     File separator    bin    File separator    java       private static void appendVMArgs Collection lt String gt  cmd        Collection lt String gt  vmArguments   ManagementFactory getRuntimeMXBean   getInputArguments         String javaToolOptions   System getenv  JAVA TOOL OPTIONS        if  javaToolOptions    null            Collection lt String gt  javaToolOptionsList   Arrays asList javaToolOptions split                vmArguments   new ArrayList lt  gt  vmArguments           vmArguments removeAll javaToolOptionsList              cmd addAll vmArguments      private static void appendClassPath List lt String gt  cmd        cmd add  -cp        cmd add ManagementFactory getRuntimeMXBean   getClassPath            private static void appendEntryPoint List lt String gt  cmd        StackTraceElement   stackTrace            new Throwable   getStackTrace        StackTraceElement   stackTraceElement     stackTrace stackTrace length - 1       String              fullyQualifiedClass   stackTraceElement getClassName        String              entryMethod           stackTraceElement getMethodName        if   entryMethod equals  main            throw new AssertionError  Entry point is not a  main         fullyQualifiedClass         entryMethod        cmd add fullyQualifiedClass      private static void appendArgs List lt String gt  cmd  String   args        cmd addAll Arrays asList args        V1 1 Bugfix  null pointer if JAVA TOOL OPTIONS is not set    Example     java -cp Temp jar Temp a b c d e   usr lib jvm java-8-openjdk-amd64 jre bin java  -cp  Temp jar  Temp  a  b  c  d    usr lib jvm java-8-openjdk-amd64 jre bin java  -cp  Temp jar  Temp  a  b  c    usr lib jvm java-8-openjdk-amd64 jre bin java  -cp  Temp jar  Temp  a  b    usr lib jvm java-8-openjdk-amd64 jre bin java  -cp  Temp jar  Temp  a    usr lib jvm java-8-openjdk-amd64 jre bin java  -cp  Temp jar  Temp

User · Answer

Strictly speaking  a Java program cannot restart itself since to do so it must kill the JVM in which it is running and then start it again  but once the JVM is no longer running  killed  then no action can be taken   You could do some tricks with custom classloaders to load  pack  and start the AWT components again but this will likely cause lots of headaches with regard to the GUI event loop   Depending on how the application is launched  you could start the JVM in a wrapper script which contains a do while loop  which continues while the JVM exits with a particular code  then the AWT app would have to call System exit RESTART CODE    For example  in scripting pseudocode   DO     Launch the awt program   EXIT CODE     Get the exit code of the last process WHILE  EXIT CODE    RESTART CODE    The AWT app should exit the JVM with something other than the RESTART CODE on  normal  termination which doesn t require restart

User · Answer

Old question and all of that   But this is yet another way that offers some advantages   On Windows  you could ask the task scheduler to start your app again for you   This has the advantage of waiting a specific amount of time before the app is restarted   You can go to task manager and delete the task and it stops repeating   SimpleDateFormat hhmm   new SimpleDateFormat  kk mm        Calendar aCal   Calendar getInstance     aCal add Calendar SECOND  65   String nextMinute   hhmm format aCal getTime       Task Scheduler Doesn t accept seconds and won t do current minute  String   create     c   windows  system32  schtasks exe     CREATE     F     TN    RestartMyProg     SC    ONCE     ST   nextMinute    TR    java -jar c   my  dev  RestartTest jar      Process proc   Runtime getRuntime   exec create  null  null   System out println  Exit Now    try  Thread sleep 1000    catch  Exception e       just so you can see it better System exit 0

User · Answer

Eclipse typically restarts after a plugin is installed  They do this using a wrapper eclipse exe  launcher app  for windows  This application execs the core eclipse runner jar and if the eclipse java application terminates with a relaunch code  eclipse exe restarts the workbench  You can build a similar bit of native code  shell script or another java code wrapper to achieve the restart

User · Answer

Just adding information which is not present in other answers   If procfs  proc self cmdline is available  If you are running in an environment which provides procfs and therefore has the  proc file system available  which means this is not a portable solution   you can have Java read  proc self cmdline in order to restart itself  like this   public static void restart   throws IOException       new ProcessBuilder getMyOwnCmdLine    inheritIO   start      public static String   getMyOwnCmdLine   throws IOException       return readFirstLine   proc self cmdline   split   u0000      public static String readFirstLine final String filename  throws IOException       try  final BufferedReader in   new BufferedReader new FileReader filename              return in readLine              On systems with  proc self cmdline available  this probably is the most elegant way of how to  restart  the current Java process from Java  No JNI involved  and no guessing of paths and stuff required  This will also take care of all JVM options passed to the java binary  The command line will be exactly identical to the one of the current JVM process   Many UNIX systems including GNU Linux  including Android  nowadays have procfs However on some like FreeBSD  it is deprecated and being phased out  Mac OS X is an exception in the sense that it does not have procfs  Windows also does not have procfs  Cygwin has procfs but it s invisible to Java because it s only visible to applications using the Cygwin DLLs instead of Windows system calls  and Java is unaware of Cygwin   Don t forget to use ProcessBuilder inheritIO    The default is that stdin   stdout   stderr  in Java called System in   System out   System err  of the started Process are set to pipes which allow the currently running process to communicate with the newly started process  If you want to restart the current process  this is most likely not what you want  Instead you would want that stdin   stdout   stderr are the same as those of the current VM  This is called inherited  You can do so by calling inheritIO   of your ProcessBuilder instance   Pitfall on Windows  A frequent use case of a restart   function is to restart the application after an update  The last time I tried this on Windows this was problematic  When overwrote the application s  jar file with the new version  the application started to misbehave and giving exceptions about the  jar file  I m just telling  in case this is your use case  Back then I solved the issue by wrapping the application in a batch file and using a magic return value from System exit   that I queried in the batch file and had the batch file restart the application instead

User · Answer

import java io File  import java io IOException  import java lang management ManagementFactory   public class Main       public static void main String   args  throws IOException  InterruptedException           StringBuilder cmd   new StringBuilder            cmd append System getProperty  java home     File separator    bin    File separator    java             for  String jvmArg   ManagementFactory getRuntimeMXBean   getInputArguments                  cmd append jvmArg                           cmd append  -cp    append ManagementFactory getRuntimeMXBean   getClassPath    append               cmd append Main class getName    append               for  String arg   args                cmd append arg  append                         Runtime getRuntime   exec cmd toString             System exit 0             Dedicated to all those who say it is impossible   This program collects all information available to reconstruct the original commandline  Then  it launches it and since it is the very same command  your application starts a second time  Then we exit the original program  the child program remains running  even under Linux  and does the very same thing   WARNING  If you run this  be aware that it never ends creating new processes  similar to a fork bomb

User · Answer

If you realy need to restart your app  you could write a separate app the start it     This page provides many different examples for different scenarios   http   www rgagnon com javadetails java-0014 html

[java] How can I restart a Java application?

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