I'm trying to launch an external program from my java swing app using this:
Process proc = Runtime.getRuntime().exec(cmd);
But the external program never actually gets launched until I close out of my java app...everytime.
It waits to launch only after I have closed out.
the external program I am trying to run is an exe that takes arguments so:
cmd = "externalProgram.exe -v --fullscreen --nowing";
What could possibly be wrong here.
Funny enough it works as expected if i try something simple like:
Process proc = Runtime.getRuntime().exec("notepad.exe");
You may need to read from the process's standard output, or close the standard input, before it will proceed. For reading the output, the problem is that the buffer can get full, blocking the program; for closing the input, the problem is that some programs will try to read data from there if it's available, waiting to do so. One or both of these tricks is very likely to straighten things out for you.
You may also read the error output stream to check it the program is actually being unsuccessfully executed
String cmd = "svn.exe";
Process proc = Runtime.getRuntime().exec(cmd);
BufferedReader reader = new BufferedReader(new InputStreamReader(proc.getErrorStream()));
String line = null;
while((line=reader.readLine())!=null){
System.out.println(line);
}
reader.close();
My console shows
Type 'svn help' for usage.
Which evidently shows the program was executed by Java.
Related
I've been trying to use Java's ProcessBuilder to launch an application in Linux that should run "long-term". The way this program runs is to launch a command (in this case, I am launching a media playback application), allow it to run, and check to ensure that it hasn't crashed. For instance, check to see if the PID is still active, and then relaunch the process, if it has died.
The problem I'm getting right now is that the PID remains alive in the system, but the GUI for the application hangs. I tried shifting the ProcessBuilder(cmd).start() into a separate thread, but that doesn't seem to be solving anything, as I hoped it would have.
Basically the result is that, to the user, the program APPEARS to have crashed, but killing the Java process that drives the ProcessBuilder.start() Process actually allows the created Process to resume its normal behavior. This means that something in the Java application is interfering with the spawned Process, but I have absolutely no idea what, at this point. (Hence why I tried separating it into another thread, which didn't seem to resolve anything)
If anyone has any input/thoughts, please let me know, as I can't for the life of me think of how to solve this problem.
Edit: I have no concern over the I/O stream created from the Process, and have thus taken no steps to deal with that--could this cause a hang in the Process itself?
If the process writes to stderr or stdout, and you're not reading it - it will just "hang" , blocking when writing to stdout/err. Either redirect stdout/err to /dev/null using a shell or merge stdout/err with redirectErrorStream(true) and spawn another thread that reads from stdout of the process
You want the trick?
Don't start your process from ProcessBuilder.start(). Don't try to mess with stream redirection/consumption from Java (especially if you give no s**t about it ; )
Use ProcessBuilder.start() to start a little shell script that gobbles all the input/output streams.
Something like that:
#!/bin/bash
nohup $1 >/dev/null 2>error.log &
That is: if you don't care about stdout and still want to log stderr (do you?) to a file (error.log here).
If you don't even care about stderr, just redirect it to stdout:
#!/bin/bash
nohup $1 >/dev/null 2>1 &
And you call that tiny script from Java, giving it as an argument the name of the process you want to run.
If a process running on Linux that is redirecting both stdout and stderr to /dev/null still produce anything then you've got a broken, non-compliant, Linux install ;)
In other word: the above Just Works [TM] and get rid of the problematic "you need to consume the streams in this and that order bla bla bla Java-specific non-sense".
The thread running the process may block if it does not handle the output. This can be done by spawning a new thread that reads the output of the process.
final ProcessBuilder builder = new ProcessBuilder("script")
.redirectErrorStream(true)
.directory(workDirectory);
final Process process = builder.start();
final StringWriter writer = new StringWriter();
new Thread(new Runnable() {
public void run() {
IOUtils.copy(process.getInputStream(), writer);
}
}).start();
final int exitValue = process.waitFor();
final String processOutput = writer.toString();
Just stumbled on this after I had a similar issue. Agreeing with nos, you need to handle the output. I had something like this:
ProcessBuilder myProc2 = new ProcessBuilder(command);
final Process process = myProc2.start();
and it was working great. The spawned process even did output some output but not much. When I started to output a lot more, it appeared my process wasn't even getting launched anymore. I updated to this:
ProcessBuilder myProc2 = new ProcessBuilder(command);
myProc2.redirectErrorStream(true);
final Process process = myProc2.start();
InputStream myIS = process.getInputStream();
String tempOut = convertStreamToStr(myIS);
and it started working again. (Refer to this link for convertStreamToStr() code)
Edit: I have no concern over the I/O stream created from the Process, and have thus taken no steps to deal with that--could this cause a hang in the Process itself?
If you don't read the output streams created by the process then it is possible that the application will block once the application's buffers are full. I've never seen this happen on Linux (although I'm not saying that it doesn't) but I have seen this exact problem on Windows. I think this is likely related.
JDK7 will have builtin support for subprocess I/O redirection:
http://download.oracle.com/javase/7/docs/api/java/lang/ProcessBuilder.html
In the meantime, if you really want to discard stdout/stderr, it seems best (on Linux) to invoke ProcessBuilder on a command that looks like:
["/bin/bash", "-c", "exec YOUR_COMMAND_HERE >/dev/null 2>&1"]
Another solution is to start the process with Redirect.PIPE and close the InputStream like this:
ProcessBuilder builder = new ProcessBuilder(cmd);
builder.redirectOutput(Redirect.PIPE);
builder.redirectErrorStream(true); // redirect the SysErr to SysOut
Process proc = builder.start();
proc.getInputStream().close(); // this will close the pipe and the output will "flow"
proc.waitFor(); //wait
I tested this in Windows and Linux, and works!
In case you need to capture stdout and stderr and monitor the process then using Apache Commons Exec helped me a lot.
I believe the problem is the buffering pipe from Linux itself.
Try to use stdbuf with your executable
new ProcessBuilder().command("/usr/bin/stdbuf","-o0","*executable*","*arguments*");**
The -o0 says not to buffer the output.
The same goes to -i0 and -e0 if you want to unbuffer the input and error pipe.
you need to read the output before waiting to finish the cycle. You will not be notified If the output doesn't fill the buffer. If it does, it will wait until you read the output.
Suppose you have some errors or responses regarding your command which you are not reading. This would cause the application to stop and waitFor to wait forever. A simple way around is to re-direct the errors to the regular output.
I was spent 2 days on this issue.
public static void exeCuteCommand(String command) {
try {
boolean isWindows = System.getProperty("os.name").toLowerCase().startsWith("windows");
ProcessBuilder builder = new ProcessBuilder();
if (isWindows) {
builder.command("cmd.exe", "/c", command);
} else {
builder.command("sh", "-c", command);
}
Process process = builder.start();
BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line;
while ((line = reader.readLine()) != null)
System.out.println("Cmd Response: " + line);
process.waitFor();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
I have a Java application that calls a tcsh script which in turn calls a perl script in the same directory. If I run this script from the command by typing "runPerlScript.sh", it works completely fine, and generates several output files as it should. However, if I call the script from Java, using the code below:
String[] runCmd = {"/bin/tcsh","-c","/filepath/runPerlScript.sh"};
Process run = Runtime.getRuntime().exec(runCmd);
BufferedReader reader = new BufferedReader(new InputStreamReader(run.getInputStream()));
String line = "";
line = reader.readLine();
System.out.println("\nStarting while.");
while((line)!=null){
System.out.println("Output from script: "+line);
line=reader.readLine();
}
reader.close();
System.out.println("Finished running perl script.");
it prints out the echo statements from my shell script to my console (I'm using NetBeans), but generates only 4 output files (when normally it generates near 50). It seems as if the process is quitting to early, because after these 4 files are generated, an echo statement in my shell script that says "Finished running runPerlScript.sh" prints out to my console. I've tried several different ways to run this script, including ProcessBuilder, but none seem to generate the output files. The code I have above was in fact the only way I was able to generate ANY output, because ProcessBuilder just resulted in hangups. Does anyone know how I can continuously make the script run?
From the Runtime.exec() javadoc:
"Executes the specified string command in a separate process."
Assuming you want to wait for the process to end, you will need to wait for the process to terminate in your main java thread. The best way to do this would be by monitoring the Process returned by ProcessBuilder.start() and wait with Process.waitFor().
I want to run an executable written in C++ and to see the cmd promt associated with it in foreground, since the executable prints some lines in the cmd.
I have written the following code, but all processes are created and run in background (In this code I open the dummy cmd.exe process, not my process).
Process p = new ProcessBuilder("C:\\Windows\\System32\\cmd.exe").start();
How can i enable foreground running of processes?
Thanks!
The issue is not whether the process is in the foreground or background. When you start a process using Java, you have to use Java to control that process' lifecyle. The Java API provides you access to various attributes of the process. What you're interested in here is the output of the process. That is represented by the process' InputStream. It seems counterintuitive, but it makes sense because from the perspective of your Java program, the process' output is the program's input. Conversely, if you need to send data to the process, you write to the process' OutputStream.
To sum up, access the process' InputStream and print that out to the command-line:
Process process = new ProcessBuilder("C:\\Path\\To\\My\\Application.exe").start();
BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
StringBuilder output = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
output.append(line);
}
System.out.println(line);
This code, of course, assumes that your process is not waiting for any input, i.e., it is not interactive.
Vivin Paliath's answer is really the way to go, then you can do whatever you want with the output, display it in your own dialogue, log it, interpret it, check for errors or whatever.
But just in case you really want that command window showing up. Execute cmd.exe and get the process' OutputStream and write the command (application.exe) to it ending with a new line.
Something along the lines of:
Process p = new ProcessBuilder("C:\\Windows\\System32\\cmd.exe").start();
out = p.getOutputStream();
out.write("path\\application.exe\r\n".getBytes());
out.flush();
Should usually drain the input stream too though anyway.
I want to run a shell script from a java program. This shell script invokes a system library which needs a big file as resource.
My java program calls this script for every word in a document. If I call this script again and again using Runtime.exec() the time taken is very high since the resource loading takes lot of time.
To overcome this I thought of writing the shell script as follows (to make it run continuously in background ):
count=0
while count -lt 10 ; do
read WORD
//execute command on this line
done
I need retrieve the output of the command in my java program and process it further.
How should I code the I/O operations for achieving this task?
I have tried writing words in to the process's output stream and reading back output from process's input stream. But this does not work and throws a broken pipe exception.
try {
parseResult = Runtime.getRuntime().exec(parseCommand);
parsingResultsReader = new BufferedReader(new InputStreamReader (parseResult.getInputStream()));
errorReader = new BufferedReader(new InputStreamReader (parseResult.getErrorStream()));
parseResultsWriter = new BufferedWriter(new OutputStreamWriter((parseResult.getOutputStream())));
} catch (IOException e) {
e.printStackTrace();
}
parseResultsWriter.write(word);
parseResultsWriter.flush();
while ((line = parsingResultsReader.readLine()) != null) {
// capture output in list here
}
Kindly help with this issue
//execute command on this line
Is this command a separate program? Then it will be launched for every word, so you'll get rid of only shell process which is lightweight anyway.
You have to learn how to run the heavyweight command for many words at once.
I am using Java on Windows XP and want to be able to send commands to another program such as telnet.
I do not want to simply execute another program. I want to execute it, and then send it a sequence of commands once it's running.
Here's my code of what I want to do, but it does not work:
(If you uncomment and change the command to "cmd" it works as expected. Please help.)
This is a simplified example. In production there will be many more commands sent, so please don't suggest calling "telnet localhost".
try
{
Runtime rt = Runtime.getRuntime();
String command = "telnet";
//command = "cmd";
Process pr = rt.exec(command);
BufferedReader processOutput = new BufferedReader(new InputStreamReader(pr.getInputStream()));
BufferedWriter processInput = new BufferedWriter(new OutputStreamWriter(pr.getOutputStream()));
String commandToSend = "open localhost\n";
//commandToSend = "dir\n" + "exit\n";
processInput.write(commandToSend);
processInput.flush();
int lineCounter = 0;
while(true)
{
String line = processOutput.readLine();
if(line == null) break;
System.out.println(++lineCounter + ": " + line);
}
processInput.close();
processOutput.close();
pr.waitFor();
}
catch(Exception x)
{
x.printStackTrace();
}
That looks OK, as it won't be producing that much output, but you should really read and write in separate threads so it doesn't fill up the buffer and block waiting you to read before you reach the next step.
So if it's reaching the point where you flush the command you send to it, find out whether the Windows telnet client supports receiving commands from standard input rather than a console by piping the text you're sending to its standard input to it in a command prompt.
For example, echo dir c:\ | cmd causes cmd to run, list the c: drive contents and exit, much the same behaviour as if you typed dir c:\ into the console. But echo open localhost | telnet causes telnet to clear the screen then exit, rather than behaving the same way as if you typed it into the console. As telnet needs to mask user input for passwords, it's quite likely that it's using the console API rather than reading from standard input. It's help doesn't list any command arguments to tell it to read from standard input, so maybe you need to use a telnet implementation which is better suited to scripting.
It's not directly an answer to your question, but...
Instead of using Runtime.exec() you should use a ProcessBuilder and redirect stderr to stdout (ProcessBuilder.redirectErrorStream(true)). Otherwise your process could block if it writes something to stderr (Windows doesn't like it when the output of a process isn't read).
If you want to control a telnet session programatically from Java, you might be able to use this Java telnet library... you can do the same things (open connections, send username/password, send commands and receive results) but without actually spawning a separate process.
You may take a look at the Telnet Ant task you can call it directly in your code with out having to use a build.xml file.
You can also take a look at the source code and see how they do it.