Here's the code: it successfully opens a terminal but nothing is displayed on the output
try {
String command= "/usr/bin/xterm";
Runtime rt = Runtime.getRuntime();
Process pr = rt.exec(command);
BufferedWriter os =
new BufferedWriter(new OutputStreamWriter(pr.getOutputStream()));
BufferedReader is =
new BufferedReader(new InputStreamReader(pr.getInputStream()));
String line = "";
while ((line = is.readLine()) != null) {
System.out.print(line);
}
} catch (Exception io) {
}
Don't write empty catch-blocks. It's just wrong and it will cost you many hours of debugging after which you'll feel ... less than perfect.
xterm produces no output by default. It just displays a window. Try starting xterm in a terminal and see which output it produces (in the original terminal, not in the new window!).
Read When Runtime.exec() won't and follow all of its advice.
Have you read When Runtime.exec() won't. If you read the whole article you will avoid and understand many pitfalls of the exec command.
Then you can read up on ProcessBuilder which is a more modern way to invoke other processes.
Ps. Empty catch block swallow exceptions and make it harder to debug.
Related
I am trying to print the output of a shell script on the console using java. When I manually run the script, I get
C:/Users/user1/Desktop/shell.sh: line 78: /usr/ucb/ps: No such file or directory
<STATUS>: Probe [ devicename ] is not running!
But, when I try to run it on my Java program, the output is not being printed on the console.
My code is:
ProcessBuilder processBuilder = new ProcessBuilder("C:/Program Files/Git/git-bash.exe","C:/Users/user1/Desktop/shell.sh");
try {
Process process = processBuilder.start();
StringBuilder output = new StringBuilder();
BufferedReader reader = new BufferedReader(
new InputStreamReader(process.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
output.append(line + "\n");
System.out.println(line);
}
int exitVal = process.waitFor();
if (exitVal == 0) {
System.out.println("Success!");
System.out.println(output);
System.exit(0);
} else {
//abnormal...
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
The only output I am getting is "Success". When I debugged my code, I found that the code never enters the condition
while ((line = reader.readLine()) != null)
even though, in the bash terminal, there are lines of output. Why is this happening?
I am stuck at this point and I couldn't find any other explanations for this problem. Kindly help.
You are running git-bash.exe which opens as a windows application. Although Java has access to the stdout/stderr streams of git-bash.exe, these are not necessarily the same as the stdout/err of the internal launch of your shell script within git-bash.exe.
One way to see the stdout/err of your command would be to make a java friendly version of the .sh script which launches your original sh and redirects output to a specific files which you can then access within java afterwards.
ProcessBuilder pb = new ProcessBuilder("C:/Program Files/Git/GIT-BASH.EXE","/c/Users/blah/somescript.sh");
somescript.sh:
#!/bin/sh
runtheoriginalcommand > ~/somepath.out 2> ~/somepath.err
You could also add extra args to wrapper to pass the out/err files to be used so there is no contention with any other launches or hardcoded output files.
I have a computer algebra program (called Reduce) that works in the shell in an interactive manner: launch Reduce in the shell, then you can define variables, compute this and that, and what not. Reduce prints the output into the shell. My idea is that I want to build a frontend for this text-based program that evaluates its output and converts it into a nice LaTeX style formula. For this I want to use Java.
I can start Reduce via exec(). But how can I emulate text input to the opened shell, and how can I read back what Reduce writes into the shell?
Thanks
Jens
Edit 1: Current Code
// get the shell
Runtime rt = Runtime.getRuntime();
// execute reduce
String[] commands = {"D:/Programme/Reduce/reduce.com", "", ""};
Process proc = null;
try {
proc = rt.exec(commands);
} catch (Exception e) {
System.out.println("Error!\n");
}
// get the associated input / output / error streams
BufferedReader stdInput = new BufferedReader(new InputStreamReader(proc.getInputStream()));
BufferedWriter stdOutput = new BufferedWriter(new OutputStreamWriter(proc.getOutputStream()));
BufferedReader stdError = new BufferedReader(new InputStreamReader(proc.getErrorStream()));
// read the output from the command
System.out.println("Here is the standard output of the command:\n");
String s = null;
try {
while ((s = stdInput.readLine()) != null) {
System.out.println(s);
}
} catch (Exception e) {
}
// read any errors from the attempted command
System.out.println("Here is the standard error of the command (if any):\n");
try {
while ((s = stdError.readLine()) != null) {
System.out.println(s);
}
} catch (Exception e) {
}
You need to get the streams associated with the process including the InputStream, OutputStream, and ErrorStream. You then can send messages to the process via the OutputStream and then read info from the process via the InputStream and the ErrorStream.
From some code of mine:
final ProcessBuilder pBuilder = new ProcessBuilder(TEST_PROCESS_ARRAY);
final Process proc = pBuilder.start();
procInputStream = proc.getInputStream();
errorStream = proc.getErrorStream();
errorSBuffer = new StringBuffer();
streamGobblerSb = new StreamGobblerSb(errorStream, "Autoit Error", errorSBuffer);
new Thread(streamGobblerSb).start();
final Scanner scan = new Scanner(procInputStream);
You may want to look into using the Process class.
http://docs.oracle.com/javase/7/docs/api/java/lang/Process.html
I believe you may be able to start the process, and then use getOutputStream() to feed commands into the process.
While this is not strictly an answer, I discovered that it is more convenient for me to stick with PHP's function proc_open(). That way I can include the output directly in the frontend and do not need to worry about the communication between my Java program and the html frontend.
For everybody who wants to stick to the Java method: the article http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html is a good reference.
This code works fine on Computer A and doesn't work on Computer B ... I can't understand Why..
Nothing Exceptions or anything else ....On Computer A log file was created , on computer B log file was't created.
Computer A and B have the same Java version...
Do you have any ideas?
String str = "cmd /C dir tools>1.log";
try {
Runtime.getRuntime().exec(str);
} catch (Exception e) {
e.printStackTrace();
}
PS
this code works fine on both computers
String str = "cmd /C dir tools";
You have to open the process' output stream to save the output to a file correctly.
You can do this by creating a Process object and saving that to a file:
Process p = Runtime.getRuntime().exec(str);
InputStreamReader reader = p.getInputStream();
BufferedReader buffer = new BufferedReader(reader);
String line = null;
while ((line = buffer.readLine() != null) {
//write stuff to file here
}
Going on what SLaks said -- it is your best bet to use the built-in file APIs.
Here is a link for a general tutorial
Using these APIs will take out any strange environment issues from Computer A to B...to C and so on.
public static void executeCommand(String cmd) {
try {
Process process = Runtime.getRuntime().exec(cmd, null,
new File("/usr/hadoop-0.20.2/"));
InputStream stdin = process.getInputStream();
InputStreamReader isr = new InputStreamReader(stdin);
BufferedReader br = new BufferedReader(isr);
String line;
System.out.println("<output></output>");
while ((line = br.readLine()) != null)
System.out.println(line);
InputStreamReader esr = new InputStreamReader(
process.getErrorStream());
BufferedReader errorReader = new BufferedReader(esr);
String lineError;
while ((lineError = errorReader.readLine()) != null)
System.out.println(lineError);
process.waitFor();
System.out.println("");
} catch (Exception e) {
e.printStackTrace();
}
}
Here's my code for executing a command named 'cmd'. But I cannot get realtime output through this code. The output comes out when the command finishes. I want realtime output. Is there a way to do this?
The issue you describe is most likely caused by the application you called: many applications use unbuffered I/O when connected to a terminal, but bufferen I/O when connected to a pipe. So your cmd may simply decide not to write its output in small bits, but instead in huge chunks. The proper fix is to adjust the command, to flush its output at the appropriate times. There is little you can do about this on the Java side. See also this answer.
I think you need to have a thread for handling the output.
You should try first with the cmd which run for a while
Last time, when I try with wvdial command (this wvdial will not finish until we stop it), I need a thread to read the output of wvdial
Actually, the problem is that Process.getInputStream() returns a BufferedReader.
So, even if the called subprocess flushes all its output, a read in the calling Java program will only get it if the buffer is full.
First, I saw a few Q's about this issue in the site, but didn't see any answer that solve my problem.
I have a program written in Java and it calls a cmd program written in C++. (this is an assumption since I don't have the actual source) I know the expected I/O of the C++ program, in the cmd it is two lines of output and then it waits for string input.
I know that the first output line of the program is through error stream, and I receive it properly (this is expected), but I don't get the second line in error or input stream.
I tried to write to the program right after the first line ( the error line) and didn't got stuck, but there was no response.
I tried using 3 different threads, for each stream, but again, nothing was received in input/error stream after the first line, and the program didn't respond to writing through output stream.
My initializers are:
Process p = Runtime.getRuntime().exec("c:\\my_prog.exe");
BufferedReader err = new BufferedReader(new InputStreamReader(p.getErrorStream()));
BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedWriter output = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
Is it possible at all or maybe it depends on the C++ program?
Thanks,
Binyamin
If you want to call native applications like C and C++ from Java, you need to use JNI.
I would suggest to put the input in the program when it has started, it will propably use that as input when it wants it.
Here is how I execute any command line in Java. This command line may execute any program:
private String executionCommandLine(final String cmd) {
StringBuilder returnContent = new StringBuilder();
Process pr;
try {
Runtime rt = Runtime.getRuntime();
pr = rt.exec(cmd);
BufferedReader input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
String line = null;
while ((line = input.readLine()) != null) {
returnContent.append(line);
}
input.close();
LOG.debug(returnContent.toString());
// return the exit code
pr.waitFor();
} catch (IOException e) {
LOG.error(e.getMessage());
returnContent = new StringBuilder();
} catch (InterruptedException e) {
LOG.error(e.getMessage());
returnContent = new StringBuilder();
}
return returnContent.toString();
}