Here is my problem:
I have a .bat file which has a number of commands. When I invoke this bat file from my java program using processbuilder it starts executing the commands in .bat file line by line. However when it reaches the last line which executes a perl program it hangs and the program never ends. It hangs there forever. Any idea why this might be happening. Just for your information there is no problem with the perl code and I'm able to execute
Does your perl program write to standard output?
I suspect the problem is that a Java process redirects the child process' standard output and standard error output to a pipe.
The receiving end of that pipe is connected to the java program, so any child process invoked from java that writes to standard output / error will block if you fail to read its output.
You must either eliminate the perl program's output or read the child process' output (Process.getInputStream() and/or Process.getErrorStream()) from within your java program.
Hey I was able to fix this problem. All I had to do was to include a statement in my java code which closes the output stream of the process. Without which it was waiting on the command line for the perl program to be executed forever. I'm not exactly sure about the behavior, any information would be help
Related
In UNIX, I'm supposed to write a Java file that will print "EXIT 1" to the standard error, and then exit with a status of 1.
Here is my approach..
System.err.println("EXIT 1");
System.exit(1);
Is this what I'm supposed to do?
If so, how am I supposed to use it in the Unix shells? When I compile and run it in the bash, it just prints "EXIT 1" (so it does the same thing as System.out.println, why should I use "err"?). What is the "standard error" here?
Every running program has these three streams:
Standard input (stdin), which normally comes from the keyboard. Exposed as System.in
Standard out (stdout), which normally goes to the console. Exposed as
System.out
Standard error (stderr), which normally also goes to the console. Exposed as System.err
Your program is correct – it does print to stderr. But under normal circumstances, the stderr stream goes to the console just like the stdout stream, so they are visually indistinguishable.
However, the reason you should use stderr instead of stdout for error messages, is redirection. That means that you send stderr to a file instead of the console. Meanwhile, stdout will be unaffected, because the two streams are independent.
For example, you can do this in bash, cmd, PowerShell, etc:
$ java Program 2> errors.txt
Now, all output with System.err.println() will end up in errors.txt, while System.out.println() will still go to the screen. This can help with debugging.
There are three data streams associated with nearly every process:
Standard Input: This is the stream of input into a program, either from a terminal, a console, piped output from another process, or some other means.
Standard Error: This is where all debugging and error messages should go. This is so that this sort of information can easily be separately captured from the regular output of a program. Web servers do this, by sending error messages to an error_log file via stderr, while the normal log file would be e. g. access_log.
Standard Output: This is the where all typical, expected output that a user running a program should expect to see said output appear.
Standard Output (stdout) and Standard Error (stderr) are nearly always the first and second output streams coming from a process, respectively. This allows me to do something like /path/to/my/neat/program > logs/program.log 2> logs/program.err and have output and errors nicely sorted.
I have a R script I need to call from Java and run. I tried this code: Runtime.getRuntime().exec("Rscript pathTo/R/myScript.R"). I run it from windows command it worked fine, but when I run java class with this code in Eclipse, nothing happens. The console doesnt show anything no error no logs. Can someone tell me how to run this script from Java?
By default, a Process launched from java has its standard input, standard output and standard error redirected to pipes, which you can access from within java. Unless you read from the standard output and error pipes and transfer the text to the output of the Java application yourself, no output will become visible. Furthermore, if the internal buffer of the pipe gets full, then the child application might even block while waiting for root to write its data. So the process probably will hang and never terminate.
Since Java 7, you can have the child process inherit its I/O channels from your Java application using ProcessBuilder.inheritIO. That saves you all the trouble to read from those streams yourself.
Hi I am trying to execute external program from Java program and read the stdout message in real time, without waiting for the program to exit. However, i found that there are different stdout behaviour in different .exe program, and I don't know how to handle it.
Example 1:
server1.exe is a console program. When i run it, it will continuously listening on a port. When a client is connected to it, it will generate 1 line of stdout output every 1 second. It will not exit unless i press "ctrl-C".
In a command prompt, I run this:
server1.exe > stdout.out 2> stderr.err
When client is connected to it, I found that stdout.out file will be updated in real time. Even though server1.exe is still running, I can open stdout.out file and read the stdout output in real time.
Example 2:
Similar to server1.exe, server2.exe is also a console program. When i run it, it will also continuously listening on a port. When client is connected to it, it will generate 1 line of stdout output every 1 second. It will not exit unless i press "ctrl-C".
In a command prompt, I run this:
server2.exe > stdout.out 2> stderr.err
Even though client has connected to server2.exe, I found that stdout.out file is empty. As long as server2.exe is still running, no stdout is written to stdout.out file. That file is not updated in real time. When i press ctrl-C, it suddenly write many lines of output to stdout.out file.
Assuming that i press ctrl-C at t=11, it will write all stdout output from t=1 until t=11 into the stdout.out file. Before this, at t=10, the stdout.out file is empty.
The program in example 2 is giving me problem because I am unable to read the stdout in real time in my Java program. My java program is as below:
process = Runtime.getRuntime().exec(command);
input = new BufferedReader(new InputStreamReader(process.getInputStream()));
String inputtext = null;
while ((inputtext = input.readLine()) != null)
{
//print out the text in Real Time, when the .exe program is still running
}
May i know why the program in example 2 will not generate stdout output unless I press ctrl-C?
The strange thing is, when i run that program in console window manually, I can see the stdout output printed on the console window every 1 second. But when I try to read it from Java using inputtext = input.readLine(), inputtext will be null as long as the program is still running (I have tested it by printing out inputtext). When I press ctrl-C, the BufferedReader will suddenly be filled with all the pending stdout output.
How can I read stdout of server2.exe in real time?
The way you describe things, there is some buffering happening in your second server. The server might decide to buffer output internally, unless it is connected to a live interactive console window.
While there may be ways to work around this, I would address this in the server2 source code. Whenever that application writes its once-per-second output, it should flush its output streams afterwards. Perhaps there is some option to enable that behaviour. If there isn't, and if the sources of that program are outside your control, kindly ask the developers to add flushing, in order to allow for better integration.
For short: You need to flush the buffers.
System.out.flush()
You need to do this after every chunk of relevant data written on these streams, try doing it after every line print.
I have some simple code that uses Java apache exec classes to run external processes.
Executor ex = new DefaultExecutor();
ex.setStreamHandler(new PumpStreamHandler(System.out, System.out, System.in));
CommandLine cl = new CommandLine(
"C:\\program.exe");
ex.execute(cl);
}
For certain command line programs, this works as expected and gets all the program's output into the "out" stream while accepting my own text into the "in" stream. However, for other programs, the output of the process is visible running manually from command line, but I don't get anything coming in when I run via java process.
I would like to eventually write to the stdin and retrieve and analyze stdout within the code itself.
If there a reason that I don't know of, why some programs seem to output text on the command line, yet when I run them as java processes, I don't receive anything through the streams?
This is happening in Windows.
Out of process code will not go to the same command line output unless you explicitly configure it to do so. Also, as a general rule it is better to use a logging library like log4j than to do println statements.
I have a batch file which performs the operation of listening to the microphone and converting it to text (i am using pocket sphinx).
The command I am using to run the batch file is pocketsphinx_continuous.exe -dict <dict name> -lm <language model> -hmm <acoustic model location>. The batch file starts off and keeps listening to the microphone. Whenever we finish speaking a sentence it converts it into text on the command prompt. Since this continuously running we terminate this task by Ctrl-C.
I was trying to make this into a standalone Java application. I wanted to run this batch file through Java, so i used Runtime.getRuntime().exec("cmd /c start pocketsphinx_continuous.exe ...") with all the parameters. However strangely, it starts the batch process in a separate command prompt but immediately exits. I tried to use process.waitfor(), however it simply starts executing the batch process and then terminates. I havent called process.destroy, so i am unable to figure out why it exits the batch process.
The other question is since the batch file is running continuously, after every spoken sentence has been transcribed , I wish to get the output in my Java application. I know i can redirect the batch process to a file and then read the file, was just wondering if there is a more direct process. Could you please help me figure out where I am making a mistake.
You should use Process.getInputStream() and Process.getErrorStream() to find out what messages it prints out.
If it is exiting instantly, you might need to get the exit code (Process.waitFor()) and check the error logs from the error stream.
Also, if you can post some of your code we might be able to help. In general, these problems are due to incorrectly configured paths or command strings.
A possible fix would be to use the ProcessBuilder from Java 1.5 thusly:
// Note the lack of "cmd \c" - you shouldn't need to run it in a cmd window!
ProcessBuilder pb = new ProcessBuilder("pocketsphinx_continuous.exe",
"dict", "1121.dic",
"-lm", "1121.lm",
"-hmm", "hub4/hmm");
Process p = pb.start();
// TODO for you:
// 1. Create Threads to handle the input
// 2. Store the Process instance so that you can call p.destroy() later.
// 3. If interested, have a Thread doing p.waitFor() to get the exit code.
As Joachim Sauer mentioned in the comments, this Javaworld article explains a lot of the gotchas associated with the Process API, so have a read through. I haven't had a chance to play with the improvements made in JDK7 to the Process API, and by the looks of things Oracle are improving it again for JDK8 (JEP 102).
You can also use Timer and TimerTask to schedule your batch scan process in background. You can use this to specify infinite running task.