Develop Reference

Java start python process

I'm trying to start a python script via java and send the data via socket back to the java program.
My problem is that when I start the python script after the SocketServer is created with Runtime.getRuntime().exec("python3 ~/Documents/sensor/sensorADC.py");
no connection is established and no data is transmitted.
But when I start the script manually via CLI, everything works fine.
The timing of the program start shouldn't be the problem, because I already tried different ways and orders.
The java program is a javaFx application.
EDIT: tested in Linux
2nd Edit:
private void startPythonScript () {
try {
measureProcess = Runtime.getRuntime().exec("python3 ~/Documents/sensor/sensorADC.py"));
} catch (IOException e) {
e.printStackTrace();
}
}
What am I missing?
Thank you in advance

You're close, you can pass an array to the exec method, like this:
String[] cmd = { "python3", "sensorADC.py", "~/Documents/sensor/"};
Runtime.getRuntime().exec(cmd);
and it should work.

I "solved" it.
I compiled it with pyinstaller and now it works. Python seems to be the problem here.
But I don't know why....
For others I compiled it to an executable with pyinstaller --onefile sensor.py

Running a shell script from Java returning "command not found"

I've created a java GUI using NetBeans v.8.2. Very new to Java.
One of the buttons in the GUI launches a shell script (I am aware that this is not ideal Java practice, but it is appropriate for my use case) using arguments gathered from other buttons/text fields in the GUI:
```
private void RunMacActionPerformed(java.awt.event.ActionEvent evt) {
String command[] = {scriptDirStr + "/./Master_run.sh",
projDirStr+"/",
DestDirStr+"/",
ECnonNormStr,
ECnormStr,
ProjID.getText(),
scriptDirStr +"/"};
System.out.print(Arrays.toString(command));
ProcessBuilder pb = new ProcessBuilder(command);
try {
Process p = pb.start();
} catch (IOException ex) {
Logger.getLogger(NewJFrame.class.getName()).log(Level.SEVERE, null, ex);
}
}
```
So, the idea is to launch Master_run.sh with a bunch of arguments.
Master_run.sh runs other R and python scripts, e.g.:
python2 $script_Path/array_data_extractor.py $spath >>$spath/masterOutput.txt 2>>$spath/masterErrors.txt
and
Rscript $script_Path/1_APS_generator_master.R $spath $dpath $APS_src_filename $project_ID $APS_norm_src_filename >>$spath/masterOutput.txt 2>>$spath/masterErrors.txt
and ends with
cat $spath/masterErrors.txt| mail -s $Project_title" done" myEmailAddress#gmail.com
I know the script gets launched because I get an email with the following errors:
"...line 14: python2: command not found"
and
"...line 16: Rscript: command not found"
When I run Master_run.sh with the same exact arguments from within the terminal, there are no such errors. Does anybody know what might be going wrong and/or how to fix it?
To rephrase the problem, it seems I am getting different behavior launching the same commands from within java vs. directly onto the command line.

Your shell environment is clearly different from java's environment. Try specifying the full path to python2 and Rscript. For example
/usr/local/bin/python2 $script_Path/array_data_extractor.py ...

Grab or know a error occurred in a a jar?

I am trying to write a program that calls external jars from the command line. In my code it will do java -jar test,jar args. What I want to know though is if a error occurs in this external jar, how to catch it in my java program so I can do the necessary procedure? This is a new zone of coding for me from college level so I am a little clueless.

Command-line programs returns exit status when finished executing it's work (e.g. zero when everything is ok).
You should be able to retrieve something interesting by storing the return value of your system call and test it according to what you want to do.
// Code from https://stackoverflow.com/questions/8496494/
Runtime rt = Runtime.getRuntime();
Process pr = rt.exec("java -jar test.jar args");
// Check retVal to test
int retVal = pr.waitFor();
More about this in this SO question.

Command prompt doesn't open with Runtime.getRuntime().exec

I've created a GUI (swing) that executes a batch file that contains a command prompt .exe file execution with specific parameters.
When I run the batch file manually (by double clicking it), everything is as expected.
The problem is: the command prompt window doesn't open to show progress, moreover, it doesn't really start to work (only initiated) until I exit the GUI (forking?). When it starts to work, is works somewhere in the background and seen only in the task manager.
Only a blank command prompt window is opened.
From digging little bit around, I've constructed this command that gives me same result as above:
Runtime.getRuntime().exec("cmd.exe /c start \"Encoding\" cmd.exe /c start md \"" + Gui.outputDirField.getText() + "\\encoderOutput\" & cd \"" + Gui.outputDirField.getText() + "\\encoderOutput\" & \"" + Gui._batFile + "\" & pause");
Could you please assist?
Sorry if it sounds stupid..

this way works for me:
new Thread() {
#Override public void run() {
try {
Runtime.getRuntime().exec("cmd.exe /c start " + Gui._batFile);
} catch (IOException e1) {
e1.printStackTrace();
}
}
}.run();

trashgod may be on to something. We ran into issues with paths with spaces. This is from the release notes for jre 7u21
Changes to Runtime.exec
On Windows platform, the decoding of command strings specified to Runtime.exec(String), Runtime.exec(String,String[]) and Runtime.exec(String,String[],File) methods, has been improved to follow the specification more closely. This may cause problems for applications that are using one or more of these methods with commands that contain spaces in the program name, or are invoking these methods with commands that are not quoted correctly.
For example, Runtime.getRuntime().exec("C:\\My Programs\\foo.exe bar") is an attempt to launch the program "C:\\My" with the arguments "Programs\\foo.exe" and "bar". This command is likely to fail with an exception to indicate "C:\My" cannot be found.
The example Runtime.getRuntime().exec("\"C:\\My Programs\\foo.exe\" bar") is an attempt to launch the program "\"C:\\My". This command will fail with an exception to indicate the program has an embedded quote.
Applications that need to launch programs with spaces in the program name should consider using the variants of Runtime.exec that allow the command and arguments to be specified in an array.
Alternatively, the preferred way to create operating systems processes since JDK 5.0 is using java.lang.ProcessBuilder. The ProcessBuilder class has a much more complete API for setting the environment, working directory and redirecting streams for the process.

Does your bat file requiere user interaction or why are you putting a pause on your command? If so, the Runtime.exec just runs the file with no window, why would you want a Window? >ou can get a Process object as a result from the exec, from this object you can get an InputStream (and if needed, an OutputStream) so you can print your output or interact with the process.

How do I launch a completely independent process from a Java program?

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.