I'm building a restarter for my litte program.
The basic idea is to run a process using Runtime.getRuntime().exec, that excecutes the program itself, then running System.exit(0);
this is the code that does the restarting:
Runtime.getRuntime().addShutdownHook(new Thread() {
#Override
public void run() {
try {
Runtime.getRuntime().exec(strList);
} catch (IOException e) {
e.printStackTrace();
}
}
});
// exit
System.exit(0);
Where strList is an String[] that is something like:
{"/bin/bash","-c","java -jar path/to.jar"}
Don't worry about OS portability, the program will be run exclusively on Ubuntu.
The program restarts fine, or at least a new process is running (and continuing to restart itself after a while)
The problem is after restart I loose the console, so i have no idea what is actually happening with the program.
Is there any way to start the new process in "the same window" or any way to access it (maybe by using screen?)?
Related
I'm wanting to launch the program from a Java application, with some luck. Most programs are started without problems, but some seem to not execute properly(?).
The code I'm using is very simple:
private static void exec() {
ProcessBuilder builder = new ProcessBuilder("C:\\Users\\Fillipuster\\AppData\\Local\\Discord\\Update.exe");
try {
builder.start();
} catch (IOException e) {
e.printStackTrace();
}
}
...and works for almost all executables (*.exe). Discord is purposefully placed in the example, as it is one of the programs that cause this problem. (along with Messenger For Windows and GOG Galaxy).
The behavior is simple, and the same for all executable that causes this; a command prompt quickly pops into existence and then promptly disappears (pun intended) - resulting in the application not being launched.
Sifting through Google and Stack Overflow proved a futile effort, and at this point, I'm at a complete loss.
Any help/input is much appreciated.
Thanks to John, who pointed out that even launching the the Update.exe file "manually" results in the same behavior, I've found the problem.
It seems that when launching Discord successfully, one is actually launching a shortcut that gives a parameter to the executable. In this case:
--processStart Discord.exe
This means that the following code will in fact start Discord:
private static void exec() {
ProcessBuilder builder = new ProcessBuilder("C:\\Users\\Fillipuster\\AppData\\Local\\Discord\\Update.exe", "--processStart", "Discord.exe");
try {
builder.start();
} catch (IOException e) {
e.printStackTrace();
}
}
Thanks to John and all the other commenters.
I'm writing a plugin in order to restart a server application on Linux (though I'm testing on OSX). The way I'm doing this is using a shell script which commands the application to stop, and then oversees the death of the process, safely starting a new one when the time comes.
My script works when I execute it manually from the command line. However, when I execute it from within the application, the shell process is killed along with the application.
I've tried two different methods of running the process from Java:
String scriptArgs[] = {"sh", "restart.sh", "&"};
try {
Runtime.getRuntime().exec(scriptArgs);
} catch (IOException e) {
e.printStackTrace();
}
and
ProcessBuilder processBuilder = new ProcessBuilder("sh", "restart.sh");
try {
processBuilder.directory(new File(System.getProperty("user.dir")));
processBuilder.redirectErrorStream(false);
processBuilder.start();
} catch (IOException e) {
e.printStackTrace();
}
Both of these methods gave the same result: the script was called, it successfully shut down the application, and then it died before it could continue. Is there any method to start a completely independent process from Java?
When you run a process from java you are creating a shell instance which then runs the process. The shell will only exit once this process has finished even if it is being run in the background &
To run a process in headless mode you need to use the nohup command. For details, see here.
A usage could look like this:
ProcessBuilder processBuilder = new ProcessBuilder("nohup", "sh", "restart.sh");
try {
processBuilder.directory(new File(System.getProperty("user.dir")));
processBuilder.redirectErrorStream(false);
processBuilder.start();
} catch (IOException e) {
e.printStackTrace();
}
I am using Runtime.getRuntime().exec function to launch independent GUI Java application for subroutine task.
The code used is in simple manner:
Runtime.getRuntime().exec("java -jar /home/user/jar.jar");
Executing the code doesn't cause any process launch nor error occured! ProcessBuilder has same effect.
Checked to work correctly on Windows.
As seems, on some platforms it is ignored on system level outside Java, as JRE does not return any kind of error.
EDT: I edited the code to read stderr and stdout by parallel thread to preserve main app execution:
Process p = Runtime.getRuntime().exec(runCmd);
new DaemonFailPrint(p).start();
Thread code is:
public class DaemonFailPrint extends Thread {
private Process process;
public DaemonFailPrint(Process process) {
this.process = process;
}
#Override
public void run() {
try {
process.waitFor();
String out = "";
while (process.getInputStream().available() > 0) {
out += (char) process.getInputStream().read();
}
out += System.lineSeparator();
while (process.getInputStream().available() > 0) {
out += (char) process.getErrorStream().read();
}
JOptionPane.showMessageDialog(null, out);
} catch (InterruptedException | IOException ex) {
JOptionPane.showMessageDialog(null, ex);
}
}
}
The result is: I got empty message box straight after subprocess is "launched".
The mean is Process object seems to be created and finished in same time, but no error out exists.
The Runtime::exec() does not wait for the process to exit, so if you want to detect errors in the executed program itself, you'd need to use something like:
Process process = Runtime.getRuntime().exec("java -jar /home/user/jar.jar");
int rc = process.waitFor();
if (rc != 0)
{
System.err.println("The process failed with error: " + rc);
}
It might be, that the jar is not found or cannot be executed etc., those errors you normally see on the console, but if you have no console, the only clue might be the return code.
You might also want to check here how to capture the output console:
Capturing stdout when calling Runtime.exec
Seems that you can use process.getInputStream() to connect to the output stream of the process. So you can simply copy it to the console to see what happened.
So far so good! I found the answer recently by myself, still don't have a reason why it works this way, but I suppose it's all about internal difference of handling new processes in VM's on different platforms.
I had to edit the code this way, and now it works:
String[] runcmd = {"java","-jar","/home/user/jar.jar"};
Runtime.getRuntime().exec(runcmd);
Now it seems to work perfect. As I see it fails to process the file and execute then command with parameters given as same string while no error thrown on Java code level, it's possibly lost in VM internals.
I am working on a program written in Java which, for some actions, launches external programs using user-configured command lines. Currently it uses Runtime.exec() and does not retain the Process reference (the launched programs are either a text editor or archive utility, so no need for the system in/out/err streams).
There is a minor problem with this though, in that when the Java program exits, it doesn't really quit until all the launched programs are exited.
I would greatly prefer it if the launched programs were completely independent of the JVM which launched them.
The target operating system is multiple, with Windows, Linux and Mac being the minimum, but any GUI system with a JVM is really what is desired (hence the user configurability of the actual command lines).
Does anyone know how to make the launched program execute completely independently of the JVM?
Edit in response to a comment
The launch code is as follows. The code may launch an editor positioned at a specific line and column, or it may launch an archive viewer. Quoted values in the configured command line are treated as ECMA-262 encoded, and are decoded and the quotes stripped to form the desired exec parameter.
The launch occurs on the EDT.
static Throwable launch(String cmd, File fil, int lin, int col) throws Throwable {
String frs[][]={
{ "$FILE$" ,fil.getAbsolutePath().replace('\\','/') },
{ "$LINE$" ,(lin>0 ? Integer.toString(lin) : "") },
{ "$COLUMN$",(col>0 ? Integer.toString(col) : "") },
};
String[] arr; // array of parsed tokens (exec(cmd) does not handle quoted values)
cmd=TextUtil.replace(cmd,frs,true,"$$","$");
arr=(String[])ArrayUtil.removeNulls(TextUtil.stringComponents(cmd,' ',-1,true,true,true));
for(int xa=0; xa<arr.length; xa++) {
if(TextUtil.isQuoted(arr[xa],true)) {
arr[xa]=TextDecode.ecma262(TextUtil.stripQuotes(arr[xa]));
}
}
log.println("Launching: "+cmd);
Runtime.getRuntime().exec(arr);
return null;
}
This appears to be happening only when the program is launched from my IDE. I am closing this question since the problem exists only in my development environment; it is not a problem in production. From the test program in one of the answers, and further testing I have conducted I am satisfied that it is not a problem that will be seen by any user of the program on any platform.
There is a parent child relation between your processes and you have to break that.
For Windows you can try:
Runtime.getRuntime().exec("cmd /c start editor.exe");
For Linux the process seem to run detached anyway, no nohup necessary.
I tried it with gvim, midori and acroread.
import java.io.IOException;
public class Exec {
public static void main(String[] args) {
try {
Runtime.getRuntime().exec("/usr/bin/acroread");
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("Finished");
}
}
I think it is not possible to to it with Runtime.exec in a platform independent way.
for POSIX-Compatible system:
Runtime.getRuntime().exec(new String[]{"/bin/sh", "-c", "your command"}).waitFor();
I have some observations that may help other people facing similar issue.
When you use Runtime.getRuntime().exec() and then you ignore the java.lang.Process handle you get back (like in the code from original poster), there is a chance that the launched process may hang.
I have faced this issue in Windows environment and traced the problem to the stdout and stderr streams. If the launched application is writing to these streams, and the buffer for these stream fills up then the launched application may appear to hang when it tries to write to the streams. The solutions are:
Capture the Process handle and empty out the streams continually - but if you want to terminate the java application right after launching the process then this is not a feasible solution
Execute the process call as cmd /c <<process>> (this is only for Windows environment).
Suffix the process command and redirect the stdout and stderr streams to nul using 'command > nul 2>&1'
It may help if you post a test section of minimal code needed to reproduce the problem. I tested the following code on Windows and a Linux system.
public class Main {
/**
* #param args the command line arguments
*/
public static void main(String[] args) throws Exception {
Runtime.getRuntime().exec(args[0]);
}
}
And tested with the following on Linux:
java -jar JustForTesting.jar /home/monceaux/Desktop/__TMP/test.sh
where test.sh looks like:
#!/bin/bash
ping -i 20 localhost
as well as this on Linux:
java -jar JustForTesting.jar gedit
And tested this on Windows:
java -jar JustForTesting.jar notepad.exe
All of these launched their intended programs, but the Java application had no problems exiting. I have the following versions of Sun's JVM as reported by java -version :
Windows: 1.6.0_13-b03
Linux: 1.6.0_10-b33
I have not had a chance to test on my Mac yet. Perhaps there is some interaction occuring with other code in your project that may not be clear. You may want to try this test app and see what the results are.
You want to launch the program in the background, and separate it from the parent. I'd consider nohup(1).
I suspect this would require a actual process fork. Basically, the C equivalent of what you want is:
pid_t id = fork();
if(id == 0)
system(command_line);
The problem is you can't do a fork() in pure Java. What I would do is:
Thread t = new Thread(new Runnable()
{
public void run()
{
try
{
Runtime.getRuntime().exec(command);
}
catch(IOException e)
{
// Handle error.
e.printStackTrace();
}
}
});
t.start();
That way the JVM still won't exit, but no GUI and only a limited memory footprint will remain.
I tried everything mentioned here but without success. Main parent Java process can't quit until the quit of subthread even with cmd /c start and redirecting streams tu nul.
Only one reliable solution for me is this:
try {
Runtime.getRuntime().exec("psexec -i cmd /c start cmd.cmd");
}
catch (Exception e) {
// handle it
}
I know that this is not clear, but this small utility from SysInternals is very helpful and proven. Here is the link.
One way I can think of is to use Runtime.addShutdownHook to register a thread that kills off all the processes (you'd need to retain the process objects somewhere of course).
The shutdown hook is only called when the JVM exits so it should work fine.
A little bit of a hack but effective.
I want to open file dowloaded from server with default program and wait until edit is completed (to upload changed file on server). I made this in such way:
public void init() {
try {
int fileId = Integer.valueOf(this.getParameter("id"));
System.out.println("Downloading");
String filePath = downloadFile(fileId);
String[] cmd = { "cmd.exe", "/C", "start /wait " + filePath };
System.out.println("Opening");
Process p = Runtime.getRuntime().exec(cmd);
p.waitFor();
System.out.println("Uploading");
uploadFile(filePath, fileId, address, session);
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
This is working preety good except the case if file extension is not associated with any program. Windows display dialog for chooseing program and after client make a choice process is ended and file is immediately upload on server. Have any idea how to solve it?
The problem here is that if there is no associated application with the extension, a seperate process is spawned to ask the user what application to use. There is unfortunately, not much you can do from Java, unless you know exactly what application to call, you won't be able to monitor the file editor if it's not associated with the file prior to launch.
This is an OS feature and there's no easy way around it. Depending on the file type, you might want to "guess" what application the user will use and call that directly instead of the command interpreter, but that is very risky and error prone.