My main field is .Net but recently I have got something to do with Java. I have to create a shell utility in Java that could run in background reading few database records after specified duration and do further processing. It's a kind of scheduler. Now I have few concerns:
How to make this work as a service. I want to execute it through a shell script and the utility should start running. Off course the control should get back to the calling script.
Secondly, eventually i may want to stop this process from running. How to achieve this?
I understand these are basic question but I really have no idea where to begin and what options are best for me.
Any help / advise please?
I would go for the running the program using a scheduler or a service. However, if you wish to use a bat file and do this programmatically, I have outlined a possible approach below:
In your Java program, you can get the PID programmatically, and then write it to a file:
public static void writePID(String fileLocation) throws IOException
{
// Use the engine management bean in java to find out the pid
// and to write to a file
if (fileLocation.length() == 0)
{
fileLocation = DEFAULT_PID_FILE;
}
String pid = ManagementFactory.getRuntimeMXBean().getName();
if (pid.indexOf("#") != -1)
{
pid = pid.substring(0, pid.indexOf("#"));
}
BufferedWriter writer = new BufferedWriter(new FileWriter(fileLocation));
writer.write(pid);
writer.newLine();
writer.flush();
writer.close();
}
You can then write a stop .bat file that will kill the running program in windows. You could do something like:
setlocal
IF EXIST app.pid FOR /F %%i in ('type app.pid') do TASKKILL /F /PID %%i
IF EXIST app.pid DEL app.pid
endlocal
Of course, app.pid is the file written by the Java method above.
I am not sure how you would be able to write a script that launches a java program, and reverts control on termination. I would be interested to see if anybody has a solution for that.
I assume that you are playing your java program with a Linux/Unix box.
To run your application as a daemon, you can try
nohup java YourJavaClass &
To stop your application, you can either:
kill [psIdofYourApplication]
or
fg [your application job Id]
Ctrl-C
If you want to do some postprocessing after the application receiving 'kill/stop' signal. check out addShutdownHook(Thread hook)
Or sun.misc.SignalHandler
ps ux
see pid
kill pid
Or you'd better provide a stopping script that signals the application, which does System.exit(0)
You didn't specify the platform. If on Windows you should look into integrating with the Service Control to create a Windows service. http://en.wikipedia.org/wiki/Windows_service. Once you've implemented the service hooks, it is possible to start and stop the service through the service control GUI or using net stop MyService syntax from the command line.
As I understand, you want something like this:
if ( System.in.avaliable() > 0 ) {
in = new BufferedReader( new InputStreamReader( System.in );
String InLine = in.readLine();
...
}
Am I right?
Related
In Java, I start one new Process using Runtime.exec(), and this process in turn spawns several child processes.
I want to be able to kill all the processes, and have previously been trying process.destroy() and process.destroyForcibly() - but the docs say that destroyForcibly() just calls destroy() in the default implementation and destroy() may not kill all subprocesses (I've tried and it clearly doesn't kill the child processes).
I'm now trying a different approach, looking up the PID of the parent process using the method suggested here and then calling ps repeatedly to traverse the PIDs of child processes, then killing them all using kill. (It only needs to run on Linux).
I've managed the first bit - looking up the PID, and am trying the following command to call ps to get the child PIDs:
String command = "/bin/ps --ppid " + pid;
Process process = new ProcessBuilder(command).start();
process.waitFor();
Unfortunately the 2nd line above is throwing an IOException, with the following message: java.io.IOException: Cannot run program "/bin/ps --ppid 21886": error=2, No such file or directory
The command runs fine if I paste it straight into the terminal on Ubuntu 16.04.
Any ideas would be very much appreciated.
Thanks
Calling the command you wish to run this way is always destined to fail.
Since Process does not effectively run a shell session, the command is basically handed over to the underlying OS to run. This means that it'll fail, since the path to t he program to be executed (in this case ps), is not the full one hence the error you're getting.
Also, testing whether your command works using a terminal is not correct. Using a terminal contains the notion of performing an action with an active logged in user with a correct path etc etc. All the above are not the case though when running a command through Process as these are not taken into consideration.
Furthermore, you also need to account for cases where the actual java application could be running under a different user, with a different set of permissions, paths etc.
In order for your to fix this, you can simply do either of the following:
1) Invoke your ps command using the full path to it (still not sure if it would work)
2) Change the way your create the Process object into something like: p = new ProcessBuilder("bash", "-c", command).start();
The second, will effectively run a bash session, passing in the ps command as an argument thus obtaining the desired result.
http://commons.apache.org/proper/commons-exec/tutorial.html
```
String line = "AcroRd32.exe /p /h " + file.getAbsolutePath();
CommandLine cmdLine = CommandLine.parse(line);
DefaultExecutor executor = new DefaultExecutor();
int exitValue = executor.execute(cmdLine);
```
I'm building a c sharp serviceProcess that will start a Batch file (the batch file will start a java application).
If i stop the service it kills the java process. Stopping the java process can take up to 2 minutes. The service has to wait for the java application to stop, so i made a sleep.
System.Threading.Thread.Sleep( );
Is it possible to check if the "java" process is closed and after that stop the ServiceProcess.
You can access the process using the Process-class. It allows you to get several information about a specific process. When you start the java.exe directly (using Process.Start) you already have the Process-instance.
When using a batch-file, you need to find the process, which is not a problem at all. You can find a process using Process.GetProcessesByName, but you'd find all all java-processes running on your machine.
You could try something like the following:
Process[] proc = Process.GetProcessesByName("Java");
if (proc.Count() != 0)
{
//Process Alive
Process prod = proc[0];
prod.Kill();
prod.WaitForExit();
}
else
{
//Process Dead
}
A better option would be to use the process ID(if you know it)
Warning: This will kill the first java process it finds, you need to check which one you need to kill...
I am launching a process with Runtime.getRuntime().exec()
However, once Java reaches the end of the main() loop, java will not close, unless I destroy() the process first.
Problem with that is, I need the process to keep running after Java is closed.
I pretty much want to do this
public static void main(String args[]) {
Runtime.getRuntime().exec("file.bat");
// now I want java to close, and I want file.bat to keep running
}
I tried System.exit(), it will stop my main() loop, however I think a thread or something that was started by exec() keeps running, preventing java from closing. I can't even end it in Eclipse without first exiting file.bat
Why isn't it closing? And how would I fix it?
I couldn't find anything online, and I've been experimenting for a while, so I decided to ask you guys.
Thank you,
-Alex Benoit
Figured it out. I'll share my code in case anyone else has the same question. I brought it down to 1 line.
Desktop.getDesktop().open(new File("C:\\Folder\\File"));
This is a system dependent question. I am not sure if in Windows the parent process can terminate before the child. I believe this is true in linux.
As a guideline, you should call waitFor() on the process. However, on some systems, just doing so might not be enough. As pointed out in the javadoc, the out/err stream need to be properly purged (using the streams returned by getOutputStream() and getErrorStream()) because they could keep your process from completing. To do so, I found it most appropriate to use two separate threads, one purging the err stream, the other the out stream. The calling thread (main in your case), has to do the following:
start the external process;
start a thread to purge the out stream;
start a thread to purge the err stream;
call waitFor() on the calling thread (main).
I found the above approach very robust and easy to implement (if you are familiar with threads). Please use an ExecutorService for the threads.
Launch the file with cmd for Windows Only
Older windows will probably have to use command.com instead
Runtime.getRuntime().exec("cmd /c start file.bat");
Using the start with /wait parameter waits until bat is finished without /wait it should work.
public class Command {
public static void main(String[] args) throws java.io.IOException, InterruptedException {
String path = "C:\\DOCUME~1\\\USER\\DESKTOP";
Process p = Runtime.getRuntime().exec("cmd /c start /wait " + path + "\\test.bat");
System.out.println("Waiting for batch file ...");
p.waitFor();
System.out.println("Batch file done.");
}
}
test.bat
#echo off
cls
:start
echo This is a loop
goto start
Use the command.com file to get short path name, since long path names don't get processed too well in start program.
Here is a sample I made download link below:
https://www.mediafire.com/?mu7vht3e6tto698
Your problem may be that you are not on a Windows Administrator account you could try, But this requires you to type in your Administrator password which is very stupid.
Process p = Runtime.getRuntime().exec("runas /profile /user:Administrator \"cmd.exe /c start test.bat\"");
In "C", I can run a long blocking process in the background (AND HAVE IT CONTINUE TO RUN) after the starting process has exited.
void main(void)
{
system("some_long_blocking_process &");
exit();
}
// "some_long_blocking_process" is still running here (DESIRED BEHAVIOR)
Java's getRuntime().exec() DOESN'T have this behavior. Instead, "some_long_blocking_process" ends immediately when the Java process ends.
Anyone know how I can recapture this behavior in Java?
I am using Java 1.4 (No process builder)
I specifically am looking to start the long blocking process and to exit immediately (no "waitFor(), etc.)
Things I have already tried (the process runs correctly, but I still get the same undesired behavior)
adding "nohup" and run in foreground ("nohup some_long_process")
adding "nohup" and running in background ("nohup some_long_process &")
run in foreground ("some_long_process")
run in background ("some_long_process &")
THANKS!
Thanks to all the suggestions... I've decided to use jtahlborn's answer (it worked for me)
try this:
String[] cmd = {"/bin/sh", "-c", "yourcommand args"};
Process p = Runtime.getRuntime().exec(cmd);
when redirect stream to /dev/null:
String[] cmd = {"/bin/sh", "-c", "yourcommand args > /dev/null 2>&1 &"};
Process p = Runtime.getRuntime().exec(cmd);
the only way we were able to achieve this with java was to add another layer of script. you need a simple wrapper script which invokes the app you actually want to run, e.g.:
runner.sh:
#!/bin/sh
nohup "$#" > /dev/null 2>&1 &
then invoke "/bin/sh runner.sh the real command" from your java program.
EDIT:
Have your tried this?
Runtime.getRuntime().exec("/bin/sh -c /usr/X11/bin/xterm &")
This worked for me on MacOS.
Previous answer (JDK 1.5, apologies for not reading the question correctly):
To execute a process without waiting you can use the ProcessBuilder
ProcessBuilder pb = new ProcessBuilder("/usr/X11/bin/xterm");
pb.start();
Your problem is probably due to the trailing &. Try removing it.
getRuntime().exec() is more similar to fork() and exec() than system().
system() passes the command to the shell, and it's Bash that understands that the trailing ampersand means to run the process in the background.
getRuntime().exec() parses the command using a StringTokenizer to parse the command, and doesn't do anything with the trailing ampersand. That's simply passed as the first argument to your some_long_blocking_process, which may exit out immediately on the unknown error.
Have you tried spawning a new Thread to run the executable? Try:
new Thread(new Runnable() {
#Override
public void run() {
try {
Runtime.getRuntime().exec(<your exec>);
} catch (IOException e) {
e.printStackTrace();
}
}
}).run();
This way, the main process won't shutdown until the exec has finished running (and the thread has finished).
Also, don't manually call exit() in your application unless you have some overwhelming reason to--the JVM does a good job of detecting when the application has finished on its own. This way, you won't force close threads that are running in the background.
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.