So I have a JAR program that runs and reads the output of a command line Linux app. This app is located in a temp folder, which is where my JAR is.
Here's the Java code for reading the output:
Process proc;
ProcessBuilder pb = new ProcessBuilder();
pb.command("temp/myapp", "arg1");
pb.redirectErrorStream(true);
try {
proc = pb.start();
} catch (IOException ex) {
System.out.println("ERROR: Couldn't start process");
}
scan = new Scanner(proc.getInputStream());
String line = "";
while (scan.hasNext())
line += scan.nextLine() + System.lineSeparator();
scan.close();
Later I return that String I read into of course.
Now, the problem is that Scanner throws a NullPointerException, which means that the process cannot be found or cannot be run.
The moment I take the executable out of the temp and use
pb.command("./myapp", "arg1");
My program works perfectly fine.
If I open Terminal where the JAR is, temp/myapp arg1 will return exactly what it should. It's only the Java code that cannot seem to run this inside temp.
The question is, how do I point at the CLI app inside temp, if not the way I described above?
PS: The Java app works on Windows in the same setup, using pb.command("temp/myapp", "arg1") and a Win version of myapp so this is a Linux-specific issue.
I think it is not getting the process at respective path. Try by giving the absolute path of the process and then execute. Hope it will work.
I found the solution.
ProcessBuilder's directory() method, which I also use somewhere, sets not only the working directory of the Process, but also the directory where the Process will be launched from, on Linux at least, so how my code was actually parsed on Linux was temp/temp/myapp. When I set temp as the working directory, I only had to use ./myapp to launch it from temp. On Windows (my primary platform), this is not the case, I still have to use pass temp/myapp as parameter in command().
Related
I am running Java program to call Python process using process builder as shown below,
processBuilder = new ProcessBuilder(
Arrays.asList(
"/usr/bin/python",
"/opt/gui/oc_db5.py",
"-c",
"/opt/gui/test.json")
);
processBuilder.directory(new File("/opt/gui"));
processBuilder.start();
Location of python program is under /opt/gui directory and there is one test.json file also needs to be passed as parameter, with "-c" option, However what i am seeing is that system is appending location of java program with path of JSON file and then pick the .JSON file causing issue for Python code.
What actually python program is getting is /opt/java//opt/gui/test.json. I tried ../../ as well but it didn't work with test.json file.
Is there a way i can specify .JSON file as an argument to python program?
This seemed to work for me. I mean, it fixed the directory problem.
try {
int exitCode = Runtime.getRuntime().exec("python /opt/gui/oc_db5.py -c /opt/gui/test.json", null, new File("/")).waitFor(); // run program and get exit code
} catch(Exception e) { // is there an error?
e.printStackTrace(); // print error
}
I have written some code for executing .bat file. which contains some
commands like setting java classpath,etc..And finally there is one command
which runs a Java class file.The HelloWorld class converts some xml file and generating a new xml file in some folder. When I double click .bat file, it executes fine,
but when I try to run I am not getting any output as I was getting through
double click the .bat file. How to make a batch execute and probably it would be nice
if I could see the results through Java console.
Following is MyJava code to execute the .bat file
public void run2() {
try {
String []commands = {"cmd.exe","/C","C:/MyWork/Java/classes/run.bat"} ;
Process p = Runtime.getRuntime().exec(commands);
BufferedReader in = new BufferedReader(new InputStreamReader(
p.getInputStream()));
String line = null;
while ((line = in.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
And below the some commands which has been set to .bat file
set CLASSPATH=%CLASSPATH%;C:/MyWork/Java
set CLASSPATH=%CLASSPATH%;C:/MyWork/Java/classes
java -cp test.jar;test2.jar test.HelloWorld
Tried with "/C" commad as well. It does not execute. Actually it does not give effect of double click the .bat file. Is there any other way that I can try with?
I can see the contents inside the .bat file through Eclipse console. But it does not give the desired output. Desired output means when I double click .bat file, it executes well. But through java call, I can see the contents only .
When using cmd.exe use /C-Parameter to pass command:
String []commands = {"cmd.exe","/C","C:/MyWork/Java/classes/run.bat"} ;
according to this, the Windows CMD needs the /c argument, to execute commands like this. try this:
String []commands = {"cmd.exe","/c","C:/MyWork/Java/classes/run.bat"} ;
Windows uses \ backslash for Windows and MS-DOS path delimiter. Forward slash / is accepted by Java in the java.io package and translated to be a path delimiter, but will not be directly acceptable to Windows or accepted by the cmd.exe shell.
You may also need to specify either the working directory for the batch file to be executed in, or possibly a full path to the cmd.exe command interpreter.
See: Runtime.exec (String[] cmdarray, String[] envp, File dir)
String[] commands = {"C:\\Windows\\System32\\cmd.exe", "/c",
"C:\\MyWork\\Java\\classes\\run.bat"};
File workDir = new File( "C:/MyWork");
Process process = Runtime.getRuntime().exec( commands, null, workDir);
To verify if the batch file is run at all, add a pause command to the batch file. That will keep the window open so you can verify if the batch file is launched at all, and debug this stage-by-stage.
You do not read the error output of your batch file, therefore, you'll never see any error messages printed from there or from CMD.EXE itself. In addition, the sub-program may stall and just wait for you to read the error stream.
Please see related discussions here: How to make a java program to print both out.println() and err.println() statements?
I am trying to execute an executable file and a perl script from within a java program. I have found many topics similar to this but most of them refer to windows. I know java is platform independent and it should work anyways but it doesn't. The solution I have tried already is the one based on the java Runtime and it's exec method. It works just fine on windows but since I'm porting my program on linux I need to adapt it. As I said I need to execute an executable file that I have compiled and was written in c++ which it looks like it's working but it finishes executing with an exit value of 1. I have no idea what it means but on windows it exits with 0 and that's how it should be on linux as well (?!?!). The pearl script on the other hand does not start at all. I use the command "perl script.pl" and it exits with a value of 255. Needless to say, it doesn't do what it's supposed to.
Does anybody know another way to execute these files? Or maybe where I am wrong with my implementation?
here's the code if you want to take a look at it:
This is the one for the perl script
public static void main(String[] args){
System.out.println("Starting");
try{
String[] cmd = {"perl", "cloc-1.53.pl"};
Process pr = Runtime.getRuntime().exec(cmd);
BufferedReader input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
String line=null;
while((line=input.readLine()) != null) {
System.out.println(line);
}
int exitVal = pr.waitFor();
System.out.println("Exit code: " + exitVal);
} catch (Throwable t){
t.printStackTrace();
}
}
For the compiled file I change this:
String[] cmd = {"perl", "cloc-1.53.pl"};
with:
String cmd = "./UCC";
There should be no differece in starting processes on windows and linux.
Good article http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html
Its for the old way but gives good insight.
Article converting to the new way:
From Runtime.exec() to ProcessBuilder
From my java project I want to run an external .bat file in another thread. For this purpose I use the following method:
private void posAppRunner(final String path[], final Class targetClass) {
new Thread(new Runnable() {
public void run() {
try {
String line;
Process p = Runtime.getRuntime().exec(path);
BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
while ((line = input.readLine()) != null) {
System.out.println(line);
}
input.close();
} catch (IOException e) {
LogFactory.getLog(targetClass).warn("Error when starting a PosApplication: " + e.getMessage());
}
}
}).start();
I run the following .bat file:
call chdir %~dp0
start java <_some_arguments>
So when I do it locally from IntelliJ IDEA it works correct - a cmd process appears, after that a java process appears and after that the cmd process disappears.
But when I run my java project with this method through ANT under TeamCity windows service, only cmd process appears and nothing happens after. Java process that must be started from the bat file doesn't appear. It looks like I don't read the process output but I do!
Could you expain me, how to overcome this situation?
I believe that the problem is in current working directory. I am not so familiar with bat files and do not remember by heart what does %~dp0 mean. Anyway as the first attempt try to modify your batch file to contain the hard coded path. I believe that this will work.
In this case decide what is better for you: discover the path in java code and then pass it to batch file, generate batch file on the fly, so that it contains all parameters hard coded or debug the script. for example you can remove the start java <_some_arguments> and put
echo %~dp0 > c:\temp\batlog.log
this will print the parameter to log file. Now run it as service and see what does the log file contain. Probably you will see the problem immediately.
I'm running a windows program from within java:
String command = "cmd /C start "+fileName+".bat";
Runtime rt = Runtime.getRuntime();
Process pr = rt.exec(command, null, new File(currWD));
int exitValue = pr.waitFor();
The program completes successfully (exitValue == 0) and creates a file "fileName" in the working directory. I am trying in the same routine to find the size of this file:
xmlFileSize = (new File(fileName)).length();
Java finds the file yet it appear to be empty (xmlFileSize == 0). Once Java finishes I can see, however, that the file is non-empty.
How can I resolve this? All I want is that Java can correctly assesses the size of the file created by the windows program that Java has executed.
A zero-length file indicates that the file may not exist. From the docs:
The length, in bytes, of the file denoted by this abstract pathname, or 0L if the file does not exist.
Note that you use currWD as working directory for your bat-file. You could try to do:
new File(currWD, fileName).length()
to make sure you look for the file in the right directory.
It probably has to do with executing the bat file from a command shell. What does the bat file do? Is it launching a program?
I'm guessing that the script calls or executes another program and returns which allows the shell to die. This in turn let's the java process continue while the process from the script continues executing asynchronously.
According to the Java API for Process, that's allowable which it most definitely should be (link java.lang.Process)
I credit this answer to aioobe and John. As John suggests, the external program started by the batch file spawns a process that seems to be running for a while (50-300 millisec) after the Java sub-process running the batch file has returned. I resolved the problem by introducing a pause (as suggested by aioobe) :
int exitValue = pr.waitFor();
try {Thread.currentThread().sleep(300);} catch (InterruptedException e) {e.printStackTrace();}
After the pause Java seems to be able to see the files created by the external program. Thanks again to both contributors who helped me resolve this issue!
If anyone finds a more elegant solution, please, feel welcome to post.